Misplaced Pages

#299700

128-536: The kernel of RSTS was programmed in the assembly language MACRO-11 , compiled and installed to a disk using the CILUS program , running on a DOS-11 operating system. RSTS booted into an extended version of the BASIC programming language which DEC called " BASIC-PLUS ". All of the system software CUSPS for the operating system, including the programs for resource accounting, login , logout, and managing

256-595: A binary search algorithm (with cost ⁠ O ( log ⁡ n ) {\displaystyle O(\log n)} ⁠ ) outperforms a sequential search (cost ⁠ O ( n ) {\displaystyle O(n)} ⁠ ) when used for table lookups on sorted lists or arrays. The analysis, and study of algorithms is a discipline of computer science . Algorithms are often studied abstractly, without referencing any specific programming language or implementation. Algorithm analysis resembles other mathematical disciplines as it focuses on

384-468: A flowchart offers a way to describe and document an algorithm (and a computer program corresponding to it). It has four primary symbols: arrows showing program flow, rectangles (SEQUENCE, GOTO), diamonds (IF-THEN-ELSE), and dots (OR-tie). Sub-structures can "nest" in rectangles, but only if a single exit occurs from the superstructure. It is often important to know how much time, storage, or other cost an algorithm may require. Methods have been developed for

512-491: A language-based protection system , the kernel will only allow code to execute that has been produced by a trusted language compiler . The language may then be designed such that it is impossible for the programmer to instruct it to do something that will violate a security requirement. Advantages of this approach include: Disadvantages include: Examples of systems with language-based protection include JX and Microsoft 's Singularity . Edsger Dijkstra proved that from

640-430: A serial communication connection to interact with the operator. The connection might be a local computer terminal with a 20  mA current loop interface, an RS-232 interface (either local serial port or remote connection via modem ), or by an Ethernet connection using DECnet or LAT. As many as 128 terminals (using multi-terminal service) can connect to a RSTS system, running a maximum of 63 jobs (depending on

768-407: A bug in a device driver might crash the entire system – and the fact that large kernels can become very difficult to maintain; Thompson also stated that "It is also easier for [a monolithic kernel] to turn into a mess in a hurry as it is modified." Monolithic kernels, which have traditionally been used by Unix-like operating systems, contain all the operating system core functions and

896-501: A built-in KBM. The user would start up TECO (like any other program) by running a TECO program (TECO.TEC). TECO and the affine QEDIT were the direct ancestors of the first UNIX-based text editor, ED. Most RSTS systems used CCL's to create a file (MAKE filespec), edit a file (TECO filespec), or run a TECO program (MUNG filespec, data). The following program is an example of how TECO could be used to calculate pi (currently set to 20 digits): If

1024-425: A checked copy of the request is passed through the system call. Hence, not far to travel at all. The monolithic Linux kernel can be made extremely small not only because of its ability to dynamically load modules but also because of its ease of customization. In fact, there are some versions that are small enough to fit together with a large number of utilities and other programs on a single floppy disk and still provide

1152-625: A class of specific problems or to perform a computation . Algorithms are used as specifications for performing calculations and data processing . More advanced algorithms can use conditionals to divert the code execution through various routes (referred to as automated decision-making ) and deduce valid inferences (referred to as automated reasoning ). In contrast, a heuristic is an approach to solving problems that do not have well-defined correct or optimal results. For example, although social media recommender systems are commonly called "algorithms", they actually rely on heuristics as there

1280-680: A computer-executable form, but are also used to define or document algorithms. There are many possible representations and Turing machine programs can be expressed as a sequence of machine tables (see finite-state machine , state-transition table , and control table for more), as flowcharts and drakon-charts (see state diagram for more), as a form of rudimentary machine code or assembly code called "sets of quadruples", and more. Algorithm representations can also be classified into three accepted levels of Turing machine description: high-level description, implementation description, and formal description. A high-level description describes qualities of

1408-719: A computing machine or a human who could only carry out specific elementary operations on symbols . Most algorithms are intended to be implemented as computer programs . However, algorithms are also implemented by other means, such as in a biological neural network (for example, the human brain performing arithmetic or an insect looking for food), in an electrical circuit , or a mechanical device. Step-by-step procedures for solving mathematical problems have been recorded since antiquity. This includes in Babylonian mathematics (around 2500 BC), Egyptian mathematics (around 1550 BC), Indian mathematics (around 800 BC and later),

SECTION 10

#1732773065300

1536-461: A device present on the system, or any form of communication with other processes requires the use of system calls. A system call is a mechanism that is used by the application program to request a service from the operating system. They use a machine-code instruction that causes the processor to change mode. An example would be from supervisor mode to protected mode. This is where the operating system performs actions like accessing hardware devices or

1664-468: A driver is abstraction; the function of the driver is to translate the OS-mandated abstract function calls (programming calls) into device-specific calls. In theory, a device should work correctly with a suitable driver. Device drivers are used for e.g. video cards, sound cards, printers, scanners, modems, and Network cards. At the hardware level, common abstractions of device drivers include: And at

1792-479: A final ending state. The transition from one state to the next is not necessarily deterministic ; some algorithms, known as randomized algorithms , incorporate random input. Around 825 AD, Persian scientist and polymath Muḥammad ibn Mūsā al-Khwārizmī wrote kitāb al-ḥisāb al-hindī ("Book of Indian computation") and kitab al-jam' wa'l-tafriq al-ḥisāb al-hindī ("Addition and subtraction in Indian arithmetic"). In

1920-419: A fully functional operating system (one of the most popular of which is muLinux ). This ability to miniaturize its kernel has also led to a rapid growth in the use of Linux in embedded systems . Algorithm In mathematics and computer science , an algorithm ( / ˈ æ l ɡ ə r ɪ ð əm / ) is a finite sequence of mathematically rigorous instructions, typically used to solve

2048-515: A kernel where I/O devices are handled uniformly with other processes, as parallel co-operating processes, was first proposed and implemented by Brinch Hansen (although similar ideas were suggested in 1967 ). In Hansen's description of this, the "common" processes are called internal processes , while the I/O devices are called external processes . Similar to physical memory, allowing applications direct access to controller ports and registers can cause

2176-528: A logical point of view, atomic lock and unlock operations operating on binary semaphores are sufficient primitives to express any functionality of process cooperation. However this approach is generally held to be lacking in terms of safety and efficiency, whereas a message passing approach is more flexible. A number of other approaches (either lower- or higher-level) are available as well, with many modern kernels providing support for systems such as shared memory and remote procedure calls . The idea of

2304-522: A mature product in the Version 9 revisions. DCL was installed as the primary RTS and the file system was again upgraded (now RDS1.2) to support new user account features. Passwords were encrypted using a modified DES algorithm instead of limited to six (6) characters stored in DEC Radix-50 format. Before Version 9, there was a non-user system account in the project (group) zero (the designation

2432-423: A particular (virtual) address may be different memory from what another process accesses at the same address. This allows every program to behave as if it is the only one (apart from the kernel) running and thus prevents applications from crashing each other. On many systems, a program's virtual address may refer to data which is not currently in memory. The layer of indirection provided by virtual addressing allows

2560-684: A point where it is as fast as or faster than the one that was specifically designed for the hardware, although more relevant in a general sense. Modern monolithic kernels, such as the Linux kernel , the FreeBSD kernel, the AIX kernel, the HP-UX kernel, and the Solaris kernel, all of which fall into the category of Unix-like operating systems, support loadable kernel modules , allowing modules to be loaded into

2688-592: A policy is a particular "mode of operation". Example: Because the mechanism and policy are separated, the policy can be easily changed to e.g. require the use of a security token . In minimal microkernel just some very basic policies are included, and its mechanisms allows what is running on top of the kernel (the remaining part of the operating system and the other applications) to decide which policies to adopt (as memory management, high level process scheduling, file system management, etc.). A monolithic kernel instead tends to include many policies, therefore restricting

SECTION 20

#1732773065300

2816-407: A process must be able to access the services provided by the kernel. This is implemented differently by each kernel, but most provide a C library or an API , which in turn invokes the related kernel functions. The method of invoking the kernel function varies from kernel to kernel. If memory isolation is in use, it is impossible for a user process to call the kernel directly, because that would be

2944-457: A program from one environment and the system would switch to a different environment while running a different program, and then return the user to the original environment they started with. These environments were referred to as a Runtime System ( RTS) . The term for the command line interface that most of these RTSs had was the KBM . Prior to Version 9, the systems manager needed to define which RTS

3072-525: A programmer can write structured programs using only these instructions; on the other hand "it is also possible, and not too hard, to write badly structured programs in a structured language". Tausworthe augments the three Böhm-Jacopini canonical structures : SEQUENCE, IF-THEN-ELSE, and WHILE-DO, with two more: DO-WHILE and CASE. An additional benefit of a structured program is that it lends itself to proofs of correctness using mathematical induction . By themselves, algorithms are not usually patentable. In

3200-561: A reduced price, however users needed to purchase the full version if they had a need to generate their own kernel. The file system was upgraded and given the designation RSTS Directory Structure 1 (RDS1). All previous versions of the RSTS file system are given the designation RDS0. The newer file system was designed to support more than 1700 user accounts. "It is now thought that there are well over 10,000 licensed users and at least an equal number of unlicensed users!". From 1985 to 1989, RSTS became

3328-446: A separate area of memory, user space . This separation prevents user data and kernel data from interfering with each other and causing instability and slowness, as well as preventing malfunctioning applications from affecting other applications or crashing the entire operating system. Even in systems where the kernel is included in application address spaces , memory protection is used to prevent unauthorized applications from modifying

3456-477: A sequence of operations", which would include all computer programs (including programs that do not perform numeric calculations), and any prescribed bureaucratic procedure or cook-book recipe . In general, a program is an algorithm only if it stops eventually —even though infinite loops may sometimes prove desirable. Boolos, Jeffrey & 1974, 1999 define an algorithm to be an explicit set of instructions for determining an output, that can be followed by

3584-675: A shared memory area called "Core Common," among other practices. When RSX is the default KBM , the standard RSX prompt (both logged in and logged out) is the ">" (or MCR "Monitor Console Routine") sign (example): The RT-11 RTS emulated the Single Job version of the RT-11 distribution. Like the RSX emulation, RT-11 occupied the top 8K of memory, leaving the bottom 56K for CUSPS , programs written in FORTRAN-IV or Macro Assembler. When RT-11

3712-429: A terminal through a DECserver the ability to communicate with a RSTS machine, just as easily as with a VAX running VMS . The DCL command structure between DEC operating systems also contributed to the familiar look and feel: This is not just another pseudo command file processor; it is based on VMS features. The DCL command file processor is fully supported and integrated in RSTS through extensive changes to DCL and

3840-480: A unique byte code and the variables and data being indexed and stored separately within the memory space. The internal byte-code format was known as PCODE. When the interactive SAVE command was issued, the BASIC Plus RTS simply saved the working memory area to a disk file with a ".BAC" extension. Although this format was undocumented, two Electronic Engineering undergraduates from Southampton University in

3968-554: A user is running a system program while logged out (because the system manager has enabled it) their PPN number is [0,0], and appears in the SYSTAT CUSP as **,**. Thus that is not a valid account number. If the user specifies a slash (/) instead of a comma between the project number and programmer number, a system wide message stored in [1,2]NOTICE.TXT (equivalent to the Unix motd ) will not be displayed at login. In every project,

RSTS/E - Misplaced Pages Continue

4096-400: A user typed an unrecognized command at system boot to the "Option:" prompt of INIT.SYS, the startup utility, the message "Type 'HELP' for help" was displayed. If the user subsequently typed 'HELP' (including the quotes) to the prompt, the response was "How amusing, anyway..." followed by the actual help message. A system manager could compile into the kernel a rotating display pattern that gave

4224-449: A user-level application may only be permitted to perform some of these operations (e.g., it may only be allowed to read the file). A common implementation of this is for the kernel to provide an object to the application (typically so called a "file handle") which the application may then invoke operations on, the validity of which the kernel checks at the time the operation is requested. Such a system may be extended to cover all objects that

4352-478: A violation of the processor's access control rules. A few possibilities are: An important consideration in the design of a kernel is the support it provides for protection from faults ( fault tolerance ) and from malicious behaviours ( security ). These two aspects are usually not clearly distinguished, and the adoption of this distinction in the kernel design leads to the rejection of a hierarchical structure for protection . The mechanisms or policies provided by

4480-478: Is [0,1]), and all accounts in project number 1 were privileged (not unlike the root account on Unix systems). With the release of Version 9, additional accounts could be created for project zero, and multiple privileges could be individually set for any account. Support for the LAT protocol was included, as well as the ability to run the newest version of DECnet IV. These network enhancements give any user connected to

4608-575: Is a computer program at the core of a computer 's operating system and generally has complete control over everything in the system. The kernel is also responsible for preventing and mitigating conflicts between different processes. It is the portion of the operating system code that is always resident in memory and facilitates interactions between hardware and software components. A full kernel controls all hardware resources (e.g. I/O, memory, cryptography) via device drivers , arbitrates conflicts between processes concerning such resources, and optimizes

4736-447: Is a computer program encapsulating, monitoring and controlling a hardware device (via its Hardware/Software Interface (HSI) ) on behalf of the OS. It provides the operating system with an API, procedures and information about how to control and communicate with a certain piece of hardware. Device drivers are an important and vital dependency for all OS and their applications. The design goal of

4864-416: Is a method or mathematical process for problem-solving and engineering algorithms. The design of algorithms is part of many solution theories, such as divide-and-conquer or dynamic programming within operation research . Techniques for designing and implementing algorithm designs are also called algorithm design patterns, with examples including the template method pattern and the decorator pattern. One of

4992-581: Is a more specific classification of algorithms; an algorithm for such problems may fall into one or more of the general categories described above as well as into one of the following: One of the simplest algorithms finds the largest number in a list of numbers of random order. Finding the solution requires looking at every number in the list. From this follows a simple algorithm, which can be described in plain English as: High-level description: (Quasi-)formal description: Written in prose but much closer to

5120-423: Is a notable example of microkernel design. The Linux kernel is both monolithic and modular, since it can insert and remove loadable kernel modules at runtime. This central component of a computer system is responsible for executing programs. The kernel takes responsibility for deciding at any time which of the many running programs should be allocated to the processor or processors. Random-access memory (RAM)

5248-498: Is always displayed in decimal. Protections indicate if the file may be seen by any other user, by other users with the same programmer number, if the file is read only or if it may be altered by another user, and whether the file may be executed by an ordinary user giving them additional privileges. These protection codes are very similar to the r, w and x protections in Unix and similar operating systems such as BSD and Linux . Code 60

RSTS/E - Misplaced Pages Continue

5376-423: Is an example of inter-process communication (IPC). The above listed tasks and features can be provided in many ways that differ from each other in design and implementation. The principle of separation of mechanism and policy is the substantial difference between the philosophy of micro and monolithic kernels. Here a mechanism is the support that allows the implementation of many different policies, while

5504-420: Is an exokernel. In a monolithic kernel, all OS services run along with the main kernel thread, thus also residing in the same memory area. This approach provides rich and powerful hardware access. UNIX developer Ken Thompson stated that "it is in [his] opinion easier to implement a monolithic kernel". The main disadvantages of monolithic kernels are the dependencies between system components –

5632-499: Is common in conventional commercial systems; in fact, every module needing protection is therefore preferably included into the kernel. This link between monolithic design and "privileged mode" can be reconducted to the key issue of mechanism-policy separation; in fact the "privileged mode" architectural approach melds together the protection mechanism with the security policies, while the major alternative architectural approach, capability-based addressing , clearly distinguishes between

5760-456: Is equivalent to a private file, code 63 is a private non-deletable file, and 40 is a public file. Library files are kept in account [1,1] and it is usually referenced by the logical name LB:. The account [1,2] is the system startup account (much like a Unix system starting up under root), and contains the system CUSPS that could be referenced by prefixing the CUSP name with a dollar sign ($ ). "!"

5888-460: Is no truly "correct" recommendation. As an effective method , an algorithm can be expressed within a finite amount of space and time and in a well-defined formal language for calculating a function . Starting from an initial state and initial input (perhaps empty ), the instructions describe a computation that, when executed , proceeds through a finite number of well-defined successive states, eventually producing "output" and terminating at

6016-570: Is only valid on the SIMH PDP-11 emulator. The license also covers some other Digital operating systems. Copies of the license are included in an authorized software kit available for download on the official website of the SIMH emulator. The standard complement of documentation manuals that accompanies a RSTS distribution consists of at least 11 large three-ring binders (collectively known as "The orange wall"), one small three-ring binder containing

6144-466: Is printed on the terminal. Prior to Version 9, a user can also initiate a 1 line login, however this leaves the user's password on the screen for anyone else in the room to view (examples follow): or or The status of a terminal can be determined from the command responses, printed by the command interpreter. A logged-in user communicating with the BASIC-PLUS KBM (key board monitor) is given

6272-505: Is that any security policy can be implemented in an application regardless of kernel support. According to Mars Research Group developers, a lack of isolation is one of the main factors undermining kernel security. They propose their driver isolation framework for protection, primarily in the Linux kernel. Typical computer systems today use hardware-enforced rules about what programs are allowed to access what data. The processor monitors

6400-476: Is the default KBM , the standard RT-11 prompt (both logged in and logged out) is the "." sign (example): The TECO editor was itself implemented as an RTS to maximize the amount of memory available for the editing buffer, and also because it was first implemented in RSTS V5B, before the release of the general purpose runtime systems (RSX and RT11). TECO was the only RTS distributed with RSTS that did not contain

6528-452: Is to simulate capabilities using commonly supported hierarchical domains. In this approach, each protected object must reside in an address space that the application does not have access to; the kernel also maintains a list of capabilities in such memory. When an application needs to access an object protected by a capability, it performs a system call and the kernel then checks whether the application's capability grants it permission to perform

SECTION 50

#1732773065300

6656-441: Is typically implemented using CPU modes . Many kernels provide implementation of "capabilities", i.e., objects that are provided to user code which allow limited access to an underlying object managed by the kernel. A common example is file handling: a file is a representation of information stored on a permanent storage device. The kernel may be able to perform many different operations, including read, write, delete or execute, but

6784-458: Is used for account [1,3], "%" for [1,4] and "&" for [1,5]. The account [1,1] also had the special privilege of being the only account where a user logged in under that account is permitted to execute the POKE system call to put values into any memory in the system. Thus the account number [1,1] is the closest equivalent to "root" on Unix-based systems. One of the features of RSTS is the means for

6912-663: Is used to store both program instructions and data. Typically, both need to be present in memory in order for a program to execute. Often multiple programs will want access to memory, frequently demanding more memory than the computer has available. The kernel is responsible for deciding which memory each process can use, and determining what to do when not enough memory is available. I/O devices include, but are not limited to, peripherals such as keyboards, mice, disk drives, printers, USB devices, network adapters, and display devices . The kernel provides convenient methods for applications to use these devices which are typically abstracted by

7040-453: Is useful for uncovering unexpected interactions that affect performance. Benchmarks may be used to compare before/after potential improvements to an algorithm after program optimization. Empirical tests cannot replace formal analysis, though, and are non-trivial to perform fairly. To illustrate the potential improvements possible even in well-established algorithms, a recent significant innovation, relating to FFT algorithms (used heavily in

7168-1107: The Entscheidungsproblem (decision problem) posed by David Hilbert . Later formalizations were framed as attempts to define " effective calculability " or "effective method". Those formalizations included the Gödel – Herbrand – Kleene recursive functions of 1930, 1934 and 1935, Alonzo Church 's lambda calculus of 1936, Emil Post 's Formulation 1 of 1936, and Alan Turing 's Turing machines of 1936–37 and 1939. Algorithms can be expressed in many kinds of notation, including natural languages , pseudocode , flowcharts , drakon-charts , programming languages or control tables (processed by interpreters ). Natural language expressions of algorithms tend to be verbose and ambiguous and are rarely used for complex or technical algorithms. Pseudocode, flowcharts, drakon-charts, and control tables are structured expressions of algorithms that avoid common ambiguities of natural language. Programming languages are primarily for expressing algorithms in

7296-629: The Jacquard loom , a precursor to Hollerith cards (punch cards), and "telephone switching technologies" led to the development of the first computers. By the mid-19th century, the telegraph , the precursor of the telephone, was in use throughout the world. By the late 19th century, the ticker tape ( c.  1870s ) was in use, as were Hollerith cards (c. 1890). Then came the teleprinter ( c.  1910 ) with its punched-paper use of Baudot code on tape. Telephone-switching networks of electromechanical relays were invented in 1835. These led to

7424-401: The compiler . Approaches that delegate enforcement of security policy to the compiler and/or the application level are often called language-based security . The lack of many critical security mechanisms in current mainstream operating systems impedes the implementation of adequate security policies at the application abstraction level . In fact, a common misconception in computer security

7552-408: The memory management unit . Generally the operating system provides a library that sits between the operating system and normal user programs. Usually it is a C library such as Glibc or Windows API. The library handles the low-level details of passing information to the kernel and switching to supervisor mode. System calls include close, open, read, wait and write. To actually perform useful work,

7680-453: The processor being used, the amount of memory and disk space, and the system load ). Most RSTS systems had far fewer terminals. Users can also submit jobs to be run in batch mode. There is also a batch program called "ATPK" that allows users to run a series of commands on an imaginary terminal (pseudo-terminal) in semi-interactive mode similar to batch commands in MS-DOS . Users connect to

7808-619: The "Control-T" one line status option which could tell the user what program they were running, under what RTS the program was using, how much memory the program was taking, how much it could expand to, and how much memory the RTS was using. Programs written in BASIC-PLUS ran under the BASIC RTS , which allowed them up to 32K bytes of memory (out of 64K total). The language was interpreted, each different keyword being internally converted to

SECTION 60

#1732773065300

7936-792: The Ifa Oracle (around 500 BC), Greek mathematics (around 240 BC), and Arabic mathematics (around 800 AD). The earliest evidence of algorithms is found in ancient Mesopotamian mathematics. A Sumerian clay tablet found in Shuruppak near Baghdad and dated to c.  2500 BC describes the earliest division algorithm . During the Hammurabi dynasty c.  1800  – c.  1600 BC , Babylonian clay tablets described algorithms for computing formulas. Algorithms were also used in Babylonian astronomy . Babylonian clay tablets describe and employ algorithmic procedures to compute

8064-566: The RSTS/E Quick Reference Guide and a paperback copy of Introduction to BASIC AA-0155B-TK . Each of the 11 three-ring binders contains: Volume 1: General Information and Installation Volume 2: System Management Volume 3: System Usage Volume 4: Utilities Volume 4A: Utilities Volume 4B: Utilities Volume 5: BASIC-PLUS Volume 6: System Programming Volume 7: MACRO Programming Volume 7A: MACRO Programming Volume 8: RMS [ Record Management Services ] RSTS uses

8192-475: The UK (Nick de Smith and David Garrod) developed a decompiler that could reverse engineer BAC files into their original BASIC-Plus source, complete with original line numbers and variable names (both subsequently worked for DEC). The rest of the memory was used by the BASIC RTS itself. If one wrote programs in a language that permitted true binary executables such as BASIC-Plus-2, FORTRAN-IV, or Macro Assembler, then

8320-596: The United States, a claim consisting solely of simple manipulations of abstract concepts, numbers, or signals does not constitute "processes" (USPTO 2006), so algorithms are not patentable (as in Gottschalk v. Benson ). However practical applications of algorithms are sometimes patentable. For example, in Diamond v. Diehr , the application of a simple feedback algorithm to aid in the curing of synthetic rubber

8448-459: The ability to control multiple terminals (128 total). Large-message send/receive and interprocess communication became very sophisticated and efficient. By August there are 1,200 licensed systems. In 1977, the installation process for RSTS was no longer dependent on DOS-11. The RSTS kernel could now be compiled under the RT-11 RTS , formatted as a kernel file with RT-11 SILUS , and copied to

8576-454: The algorithm itself, ignoring how it is implemented on the Turing machine. An implementation description describes the general manner in which the machine moves its head and stores data in order to carry out the algorithm, but does not give exact states. In the most detail, a formal description gives the exact state table and list of transitions of the Turing machine. The graphical aid called

8704-588: The algorithm's properties, not implementation. Pseudocode is typical for analysis as it is a simple and general representation. Most algorithms are implemented on particular hardware/software platforms and their algorithmic efficiency is tested using real code. The efficiency of a particular algorithm may be insignificant for many "one-off" problems but it may be critical for algorithms designed for fast interactive, commercial or long life scientific usage. Scaling from small n to large n frequently exposes inefficient algorithms that are otherwise benign. Empirical testing

8832-426: The amount of memory available would be 56K (8K allocated to the RTS ). The standard BASIC-PLUS prompt is the "Ready" response, pressing Control-T displays status (example): Starting with Version 9, DCL became the primary startup RTS even though it does not have the ability to execute binary programs. This became possible with the advent of the disappearing RSX RTS (see below). DCL was incorporated into all of

8960-403: The analysis of algorithms to obtain such quantitative answers (estimates); for example, an algorithm that adds up the elements of a list of n numbers would have a time requirement of ⁠ O ( n ) {\displaystyle O(n)} ⁠ , using big O notation . The algorithm only needs to remember two values: the sum of all the elements so far, and its current position in

9088-490: The appropriate drivers. As device management is a very OS -specific topic, these drivers are handled differently by each kind of kernel design, but in every case, the kernel has to provide the I/O to allow drivers to physically access their devices through some port or memory location. Important decisions have to be made when designing the device management system, as in some designs accesses may involve context switches , making

9216-457: The controller to malfunction, or system to crash. With this, depending on the complexity of the device, some devices can get surprisingly complex to program, and use several different controllers. Because of this, providing a more abstract interface to manage the device is important. This interface is normally done by a device driver or hardware abstraction layer. Frequently, applications will require access to these devices. The kernel must maintain

9344-399: The core of the kernel. In 1975, memory management support was again updated for the newer 22-bit addressable PDP-11/70 . RSTS systems could now be expanded to use as much as two megabytes of memory running up to 63 jobs. The RTS and CCL concepts were introduced although they had to be compiled in during " SYSGEN ". Multi-terminal service was introduced which would allow a single job

9472-478: The data requested by the program. The program can then be resumed from the point where it was stopped. This scheme is generally known as demand paging . Virtual addressing also allows creation of virtual partitions of memory in two disjointed areas, one being reserved for the kernel ( kernel space ) and the other for the applications ( user space ). The applications are not permitted by the processor to address kernel memory, thus preventing an application from damaging

9600-518: The device drivers. A monolithic kernel is one single program that contains all of the code necessary to perform every kernel-related task. Every part which is to be accessed by most programs which cannot be put in a library is in the kernel space: Device drivers, scheduler, memory handling, file systems, and network stacks. Many system calls are provided to applications, to allow them to access all those services. A monolithic kernel, while initially loaded with subsystems that may not be needed, can be tuned to

9728-521: The earliest codebreaking algorithm. Bolter credits the invention of the weight-driven clock as "the key invention [of Europe in the Middle Ages ]," specifically the verge escapement mechanism producing the tick and tock of a mechanical clock. "The accurate automatic machine" led immediately to "mechanical automata " in the 13th century and "computational machines"—the difference and analytical engines of Charles Babbage and Ada Lovelace in

9856-523: The early 12th century, Latin translations of said al-Khwarizmi texts involving the Hindu–Arabic numeral system and arithmetic appeared, for example Liber Alghoarismi de practica arismetrice , attributed to John of Seville , and Liber Algorismi de numero Indorum , attributed to Adelard of Bath . Hereby, alghoarismi or algorismi is the Latinization of Al-Khwarizmi's name; the text starts with

9984-459: The end of the decade , there are over 5,000 licensed systems. In 1981, support for separate instruction and data space for users with Unibus machines ( PDP-11/44 , PDP-11/45, PDP-11/55 and PDP-11/70) provided an extension to the memory constraints of an individual program. Compiling programs to use separate instruction and data space would soon give a program up to 64 KB for instructions, and up to 64 KB for buffering data. The DCL RTS

10112-432: The execution and stops a program that violates a rule, such as a user process that tries to write to kernel memory. In systems that lack support for capabilities, processes are isolated from each other by using separate address spaces. Calls from user processes into the kernel are regulated by requiring them to use one of the above-described system call methods. An alternative approach is to use language-based protection. In

10240-516: The execution of programs and the environment used to run them. The various environments allowed for programming in BASIC-PLUS, the enhanced and hard compiled BASIC-Plus-2, and in more traditional programming languages such as COBOL (eventually upgraded to COBOL-85) and FORTRAN IV (eventually upgraded to FORTRAN-77). Other languages were supported such as DIBOL and MUMPS . These environments were separate from each other such that one could start

10368-427: The field of image processing), can decrease processing time up to 1,000 times for applications like medical imaging. In general, speed improvements depend on special properties of the problem, which are very common in practical applications. Speedups of this magnitude enable computing devices that make extensive use of image processing (like digital cameras and medical equipment) to consume less power. Algorithm design

10496-405: The file is contiguous (is stored as one file without being separated into pieces, similar to files on a Microsoft Windows system after a drive has been defragmented ), while "P" indicates it is specially protected (cannot be deleted, even by a privileged user, unless the P bit is cleared by separate command). The numbers in brackets (like "< 40>") represent the protections for the file, which

10624-584: The final memory management update was included for all machines that could support 22-bit addressing. RSTS could now use the maximum amount of memory available to a PDP-11 (4 megabytes). Support was also included for SUPERVISORY mode which made RSTS the first DEC operating system with this capability. DECnet was also supported as well as remote diagnostics from field service technicians at the RDC in Colorado Springs, Colorado (a DEC subscription service). By

10752-418: The firmware does not support protection mechanisms, it is possible to simulate protection at a higher level, for example by simulating capabilities by manipulating page tables , but there are performance implications. Lack of hardware support may not be an issue, however, for systems that choose to use language-based protection. An important kernel design decision is the choice of the abstraction levels where

10880-408: The illusion of two snakes chasing each other around the console lights. The normal kernel would give the illusion of one snake moving from right to left in the data lights across the bottom. If the system manager also compiled the "lights" object module the user would see an additional snake moving from left to right in the address lights across the top. This was accomplished by using supervisory mode in

11008-450: The input list. If the space required to store the input numbers is not counted, it has a space requirement of ⁠ O ( 1 ) {\displaystyle O(1)} ⁠ , otherwise ⁠ O ( n ) {\displaystyle O(n)} ⁠ is required. Different algorithms may complete the same task with a different set of instructions in less or more time, space, or ' effort ' than others. For example,

11136-490: The invention of the digital adding device by George Stibitz in 1937. While working in Bell Laboratories, he observed the "burdensome" use of mechanical calculators with gears. "He went home one evening in 1937 intending to test his idea... When the tinkering was over, Stibitz had constructed a binary adding device". In 1928, a partial formalization of the modern concept of algorithms began with attempts to solve

11264-399: The kernel at runtime, permitting easy extension of the kernel's capabilities as required, while helping to minimize the amount of code running in kernel space. Most work in the monolithic kernel is done via system calls. These are interfaces, usually kept in a tabular structure, that access some subsystem within the kernel such as disk operations. Essentially calls are made within programs and

11392-425: The kernel can be classified according to several criteria, including: static (enforced at compile time ) or dynamic (enforced at run time ); pre-emptive or post-detection; according to the protection principles they satisfy (e.g., Denning ); whether they are hardware supported or language based; whether they are more an open mechanism or a binding policy; and many more. Support for hierarchical protection domains

11520-438: The kernel is usually loaded into a separate area of memory, which is protected from access by application software or other less critical parts of the operating system. The kernel performs its tasks, such as running processes, managing hardware devices such as the hard disk , and handling interrupts, in this protected kernel space . In contrast, application programs such as browsers, word processors, or audio or video players use

11648-402: The kernel itself or the kernel can also rely on other processes it is running. Although the kernel must provide IPC in order to provide access to the facilities provided by each other, kernels must also provide running programs with a method to make requests to access these facilities. The kernel is also responsible for context switching between processes or threads. The kernel has full access to

11776-431: The kernel manages, and indeed to objects provided by other user applications. An efficient and simple way to provide hardware support of capabilities is to delegate to the memory management unit (MMU) the responsibility of checking access-rights for every memory access, a mechanism called capability-based addressing . Most commercial computer architectures lack such MMU support for capabilities. An alternative approach

11904-405: The kernel so that applications do not need to know their implementation details. Key aspects necessary in resource management are defining the execution domain ( address space ) and the protection mechanism used to mediate access to the resources within a domain. Kernels also provide methods for synchronization and inter-process communication (IPC). These implementations may be located within

12032-475: The kernel will be rewritten if the available hardware changes), configured by the user (typical on older PCs and on systems that are not designed for personal use) or detected by the operating system at run time (normally called plug and play ). In plug-and-play systems, a device manager first performs a scan on different peripheral buses , such as Peripheral Component Interconnect (PCI) or Universal Serial Bus (USB), to detect installed devices, then searches for

12160-568: The kernel. The kernel's interface is a low-level abstraction layer . When a process requests a service from the kernel, it must invoke a system call , usually through a wrapper function . There are different kernel architecture designs. Monolithic kernels run entirely in a single address space with the CPU executing in supervisor mode , mainly for speed. Microkernels run most but not all of their services in user space, like user processes do, mainly for resilience and modularity . MINIX 3

12288-489: The list of these devices by querying the system for them in some way. This can be done through the BIOS, or through one of the various system buses (such as PCI/PCIE, or USB). Using an example of a video driver, when an application requests an operation on a device, such as displaying a character, the kernel needs to send this request to the current active video driver. The video driver, in turn, needs to carry out this request. This

12416-429: The mid-19th century. Lovelace designed the first algorithm intended for processing on a computer, Babbage's analytical engine, which is the first device considered a real Turing-complete computer instead of just a calculator . Although a full implementation of Babbage's second device was not realized for decades after her lifetime, Lovelace has been called "history's first programmer". Bell and Newell (1971) write that

12544-488: The monitor. DCL executes command files as part of your job; therefore, no pseudo keyboard or forcing of commands to your keyboard is necessary (as with ATPK). In 1994, DEC sold most of its PDP-11 software business to Mentec . Digital continued to support its own PDP-11 customers for a short period after with the assistance of Mentec staff. In 1997, Digital and Mentec granted anyone wishing to use RSTS 9.6 or earlier for non-commercial, hobby purposes no-cost license. The license

12672-627: The most important aspects of algorithm design is resource (run-time, memory usage) efficiency; the big O notation is used to describe e.g., an algorithm's run-time growth as the size of its input increases. Per the Church–Turing thesis , any algorithm can be computed by any Turing complete model. Turing completeness only requires four instruction types—conditional GOTO, unconditional GOTO, assignment, HALT. However, Kemeny and Kurtz observe that, while "undisciplined" use of unconditional GOTOs and conditional IF-THEN GOTOs can result in " spaghetti code ",

12800-528: The operating system to use other data stores, like a hard drive , to store what would otherwise have to remain in main memory ( RAM ). As a result, operating systems can allow programs to use more memory than the system has physically available. When a program needs data which is not currently in RAM, the CPU signals to the kernel that this has happened, and the kernel responds by writing the contents of an inactive memory block to disk (if necessary) and replacing it with

12928-445: The operation very CPU-intensive and easily causing a significant performance overhead. In computing, a system call is how a process requests a service from an operating system's kernel that it does not normally have permission to run. System calls provide the interface between a process and the operating system. Most operations interacting with the system require permissions not available to a user-level process, e.g., I/O performed with

13056-564: The phrase Dixit Algorismi , or "Thus spoke Al-Khwarizmi". Around 1230, the English word algorism is attested and then by Chaucer in 1391, English adopted the French term. In the 15th century, under the influence of the Greek word ἀριθμός ( arithmos , "number"; cf. "arithmetic"), the Latin word was altered to algorithmus . One informal definition is "a set of rules that precisely defines

13184-428: The programmer number 0 is usually reserved to as a group account, as it can be referenced by the special symbol #. If one's user number is [20,103], a reference to a file name beginning with "#" refers to a file stored in the account of the user number [20,0]. This feature is useful in educational environments, as programmer number 0 can be issued to the instructor of a class, and the individual students given accounts with

13312-568: The prompt "Ready" and a user who is logged out is given the prompt "Bye". A user logs in by supplying their PPN number and password. User numbers consist of a project number (equivalent to a group number in Unix), a comma, and a programmer number. Both numbers are in the range of 0 to 254, with special exceptions. When specifying an account, the project and programmer number are enclosed in brackets. A typical user number can be [10,5] (project 10, programmer 5), [2,146], [254,31], or [200,220], etc. When

13440-457: The recent versions of DEC's operating systems (RSX-11, RT-11, VMS , and later OpenVMS ) for compatibility. The standard DCL prompt is the dollar "$ " sign (example): Programs that were written for the RSX RTS such as COBOL, Macro Assembler, or later releases of BASIC-Plus-2, could use the maximum amount of memory available for a binary program (56K due to the requirements of an RTS needing

13568-435: The requested action, and if it is permitted performs the access for it (either directly, or by delegating the request to another user-level process). The performance cost of address space switching limits the practicality of this approach in systems with complex interactions between objects, but it is used in current operating systems for objects that are not accessed frequently or which are not expected to perform quickly. If

13696-488: The rest of the system to rely on them. Per Brinch Hansen presented arguments in favour of separation of mechanism and policy. The failure to properly fulfill this separation is one of the major causes of the lack of substantial innovation in existing operating systems, a problem common in computer architecture. The monolithic design is induced by the "kernel mode"/"user mode" architectural approach to protection (technically called hierarchical protection domains ), which

13824-454: The right in bold): The DIR command is an installed CCL equivalent to a RUN command for the DIRECT program. [0,1] is the account number (and directory name) of the operating system storage account. It would be referred to as "project number 0, programmer number 1". The numbers shown after each file represent its size in disk blocks, a block being 512 bytes or 1/2 kilobyte (K). "C" indicates

13952-435: The running kernel. This fundamental partition of memory space has contributed much to the current designs of actual general-purpose kernels and is almost universal in such systems, although some research kernels (e.g., Singularity ) take other approaches. To perform useful functions, processes need access to the peripherals connected to the computer, which are controlled by the kernel through device drivers . A device driver

14080-439: The same project number, and the instructor can store in his account files marked as shared only for that project number (which would be students in that class only, and no other). Two special classes of project numbers exist. The project number 0 is generally reserved for system software, and prior to Version 9 there is only 1 project 0 account (named [0,1]). Programmers in the project number 1 are privileged accounts, equivalent to

14208-410: The security mechanisms and policies should be implemented. Kernel security mechanisms play a critical role in supporting security at higher levels. One approach is to use firmware and kernel support for fault tolerance (see above), and build the security policy for malicious behavior on top of that (adding features such as cryptography mechanisms where necessary), delegating some responsibility to

14336-401: The single account "root" on Unix systems, except that the account numbers [1,0] through [1,254] are all privileged accounts. As of Version 9, any account can be granted specific privileges by the systems manager. The account [0,1] is used to store the operating system file itself, all run-time library systems, and certain system files relating to booting the system (author's comments appear on

14464-413: The software level, device driver abstractions include: For example, to show the user something on the screen, an application would make a request to the kernel, which would forward the request to its display driver, which is then responsible for actually plotting the character/pixel. A kernel must maintain a list of available devices. This list may be known in advance (e.g., on an embedded system where

14592-513: The system by typing the LOGIN command (or HELLO) at a logged-out terminal and pressing return. Typing any command at a logged-out terminal starts the LOGIN program which then interprets the command. If it is one of the commands which were allowed to be used by a user that is not yet logged in ("Logged Out"), then the associated program for that command is CHAINed, otherwise the message "Please say HELLO"

14720-409: The system is running by a system's manager (i.e.: it is not permanent like a disk file). When logged in, a user can "SWITCH" to any of these environments, type language statements in the BASIC-PLUS programming language, issue RUN commands to specific programs, or issue a special command called a CCL to execute a program with command options. Most RSTS systems managers generated the kernel to include

14848-403: The system or other disks, while the computer was time-sharing. The BASIC-PLUS RTS (as well as RT-11, RSX-11 , TECO and third party RTS s) all ran as user mode processes, independent of the RSTS kernel. A systems manager could now decide during the bootstrap phase which RTS to run as the systems default Keyboard Monitor ( KBM ) . By now, there were some 3,100 licensed systems. In 1978,

14976-455: The system would start under, and it had to be one that would execute compiled programs. A systems manager may also install special CCL (concise command language) commands, which take precedence over all KBM commands (with the exception of DCL ). A CCL is analogous to a shortcut to a program on a Windows system or a symbolic link on Unix-based systems. CCLs are installed as a memory-resident command either during startup, or dynamically while

15104-431: The system's memory and must allow processes to safely access this memory as they require it. Often the first step in doing this is virtual addressing , usually achieved by paging and/or segmentation . Virtual addressing allows the kernel to make a given physical address appear to be another address, the virtual address. Virtual address spaces may be different for different processes; the memory that one process accesses at

15232-413: The system, were written in BASIC-PLUS. From 1970 to 1973, RSTS ran in only 56K bytes of magnetic core memory (64 kilobytes including the memory-mapped I/O space). This would allow a system to have up to 16 terminals with a maximum of 17 jobs . The maximum program size was 16K bytes. By the end of 1973 DEC estimated there were 150 licensed systems running RSTS. In 1973, memory management support

15360-675: The time and place of significant astronomical events. Algorithms for arithmetic are also found in ancient Egyptian mathematics , dating back to the Rhind Mathematical Papyrus c.  1550 BC . Algorithms were later used in ancient Hellenistic mathematics . Two examples are the Sieve of Eratosthenes , which was described in the Introduction to Arithmetic by Nicomachus , and the Euclidean algorithm , which

15488-448: The top 8K to use for itself). RSTS Version 7 and later allowed the RSX RTS to be included in the kernel, making it completely "disappear" from the user address space, thus allowing 64K bytes of memory for user programs. Programs got around the limitations of the amount of available memory by using libraries (when permissible), by complicated overlay strategies, or by calling other programs ("Chaining") and passing them commands and data in

15616-629: The two, leading naturally to a microkernel design (see Separation of protection and security ). While monolithic kernels execute all of their code in the same address space ( kernel space ), microkernels try to run most of their services in user space, aiming to improve maintainability and modularity of the codebase. Most kernels do not fit exactly into one of these categories, but are rather found in between these two designs. These are called hybrid kernels . More exotic designs such as nanokernels and exokernels are available, but are seldom used for production systems. The Xen hypervisor, for example,

15744-432: The utilization of common resources e.g. CPU & cache usage, file systems, and network sockets. On most systems, the kernel is one of the first programs loaded on startup (after the bootloader ). It handles the rest of startup as well as memory, peripherals , and input/output (I/O) requests from software , translating them into data-processing instructions for the central processing unit . The critical code of

15872-480: The versions prior to 9.0. RSX also had a similar display pattern that would appear as if two snakes were playing chicken and would run into each other in the center of the console. The command 'make' allowed a user to make a text file and automatically enter the TECO text editor. If a user typed 'make love', the system created a file called 'love' and typed back, 'Not War?' Kernel (operating system) The kernel

16000-449: Was deemed patentable. The patenting of software is controversial, and there are criticized patents involving algorithms, especially data compression algorithms, such as Unisys 's LZW patent . Additionally, some cryptographic algorithms have export restrictions (see export of cryptography ). Another way of classifying algorithms is by their design methodology or paradigm . Some common paradigms are: For optimization problems there

16128-692: Was first described in Euclid's Elements ( c.  300 BC ). Examples of ancient Indian mathematics included the Shulba Sutras , the Kerala School , and the Brāhmasphuṭasiddhānta . The first cryptographic algorithm for deciphering encrypted code was developed by Al-Kindi , a 9th-century Arab mathematician, in A Manuscript On Deciphering Cryptographic Messages . He gave the first description of cryptanalysis by frequency analysis ,

16256-529: Was included as well as support for the newer revision of DECnet III. By 1983, with an estimated 15,000 DEC machines running RSTS/E, V8.0-06 included support for the smallest 18-bit PDP-11 sold by DEC (the MicroPDP-11). A pre-generated kernel and CUSPS were included in this distribution to make installation on the MicroPDP-11 easier. DEC sold the pre-generated version on the MicroPDP-11 as MicroRSTS at

16384-467: Was included in RSTS (now RSTS/E) for the newer DEC PDP-11/40 and PDP-11/45 minicomputers (the PDP-11/20 was only supported under RSTS-11). The introduction of memory management in the newer PDP-11 computers not only meant these machines were able to address four times the amount of memory (18-bit addressing , 256K bytes), it also paved the way for the developers to separate user mode processes from

#299700