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95-639: The Linux trademark is owned by Linus Torvalds in the U.S., Germany, the E.U., and Japan for "Computer operating system software to facilitate computer use and operation". The assignment of the trademark to Torvalds occurred after a lawsuit against attorney William R. Della Croce Jr., of Boston, who had registered the trademark in the US in September 1995 and began in 1996 to send letters to various Linux distributors, demanding ten percent of royalties from sales of Linux products. A petition against Della Croce's practices

190-404: A USB floppy drive key , an ordinary USB flash drive with the capacity to emulate floppy drives, allowing it to be used for updating system firmware where direct use of USB flash drives is not supported. The desired mode of operation, regular USB mass storage device or floppy drive emulation, is selected via sliding a switch on the device's housing. Most current PC firmware permits booting from

285-542: A micro USB plug, facilitating data transfers between different devices. Inside the casing is a small printed circuit board, which has some power circuitry and a small number of surface-mounted integrated circuits (ICs). Typically, one of these ICs provides an interface between the USB connector and the onboard memory, while the other is the flash memory . Drives typically use the USB mass storage device class to communicate with

380-428: A system call to perform a block I/O write operation, then the system call might execute the following instructions: While the writing takes place, the operating system will context switch to other processes as normal. When the device finishes writing, the device will interrupt the currently running process by asserting an interrupt request . The device will also place an integer onto the data bus. Upon accepting

475-453: A 1 TB USB-C flash drive, the smallest of its kind. [REDACTED] Internals of a typical USB flash drive On a USB flash drive, one end of the device is fitted with a single Standard-A USB plug ; some flash drives additionally offer a micro USB or USB-C plug, facilitating data transfers between different devices. On a USB flash drive, one end of the device is fitted with a single USB plug ; some flash drives additionally offer

570-493: A 2 GB drive being marketed as a 64 GB drive). When plugged into a computer, they report being the larger capacity they were sold as, but when data is written to them, either the write fails, the drive freezes up, or it overwrites existing data. Software tools exist to check and detect fake USB drives, and in some cases it is possible to repair these devices to remove the false capacity information and use its real storage limit. Transfer speeds are technically determined by

665-408: A USB drive, allowing the launch of an operating system from a bootable flash drive. Such a configuration is known as a Live USB . Original flash memory designs had very limited estimated lifetimes. The failure mechanism for flash memory cells is analogous to a metal fatigue mode; the device fails by refusing to write new data to specific cells that have been subject to many read-write cycles over

760-407: A battery to a standard flash memory control microprocessor so it can also serve as a music playback decoder. Most of these players can also be used as a conventional flash drive, for storing files of any type. There are typically five parts to a flash drive: The typical device may also include: Most USB flash drives weigh less than 30 g (1 oz). While some manufacturers are competing for

855-670: A challenging subject that depends on the SLC / MLC / TLC memory type, size of the flash memory chips, and actual usage pattern. As a result, a USB flash drive can last from a few days to several hundred years. Regardless of the endurance of the memory itself, the USB connector hardware is specified to withstand only around 1,500 insert-removal cycles. Counterfeit USB flash drives are sometimes sold with claims of having higher capacities than they actually possess. These are typically low-capacity USB drives with modified flash memory controller firmware that emulates larger capacity drives (for example,

950-645: A computer even if they are not compatible with the base operating system. A library operating system (libOS) is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with a single application and configuration code to construct a unikernel : a specialized (only the absolute necessary pieces of code are extracted from libraries and bound together ), single address space , machine image that can be deployed to cloud or embedded environments. The operating system code and application code are not executed in separated protection domains (there

1045-585: A development of MULTICS for a single user. Because UNIX's source code was available, it became the basis of other, incompatible operating systems, of which the most successful were AT&T 's System V and the University of California 's Berkeley Software Distribution (BSD). To increase compatibility, the IEEE released the POSIX standard for operating system application programming interfaces (APIs), which

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1140-568: A feature. Furthermore, for installation of Windows XP , using a USB flash drive with a storage limit of at most 2 GB is recommended in order to boot from it. In Windows Vista and later versions, ReadyBoost feature allows flash drives (from 4 GB in case of Windows Vista) to augment operating system memory. Flash drives are used to carry applications that run on the host computer without requiring installation . While any standalone application can in principle be used this way, many programs store data, configuration information, etc. on

1235-447: A few very large ones, and mixed reading and writing to the same device. In a typical well-conducted review of a number of high-performance USB 3.0 drives, a drive that could read large files at 68 MB/s and write at 46 MB/s, could only manage 14 MB/s and 0.3 MB/s with many small files. When combining streaming reads and writes the speed of another drive, the drive could read at 92 MB/s and write at 70 MB/s,

1330-553: A flash drive can be used to run installation of Windows or Linux from USB, a process that can be automated via the use of tools like the Universal USB Installer or Rufus . However, for installation of Windows 7 and later versions, using USB flash drive with hard disk drive emulation as detected in PC's firmware is recommended in order to boot from it. Transcend is the only manufacturer of USB flash drives containing such

1425-470: A flash drive with 1 TB of storage. The first USB 3.1 type-C flash drives, with read/write speeds of around 530 MB/s, were announced in March 2015. By July 2016, flash drives with 8 to 256 GB capacity were sold more frequently than those with capacities between 512 GB and 1 TB. In 2017, Kingston Technology announced the release of a 2-TB flash drive. In 2018, SanDisk announced

1520-648: A free, perpetual worldwide sublicense. LMI was headquartered in Monterey , California until at least 2005. Since at least 2009 it was headquartered in Beaverton , Oregon. This Linux -related article is a stub . You can help Misplaced Pages by expanding it . Operating system An operating system ( OS ) is system software that manages computer hardware and software resources, and provides common services for computer programs . Time-sharing operating systems schedule tasks for efficient use of

1615-445: A lack of moving parts. Additionally, they are less vulnerable to electromagnetic interference than floppy disks, and are unharmed by surface scratches (unlike CDs). However, as with any flash storage, data loss from bit leaking due to prolonged lack of electrical power and the possibility of spontaneous controller failure due to poor manufacturing could make it unsuitable for long-term archiving of data . The ability to retain data

1710-484: A large legal settlement was paid. In the twenty-first century, Windows continues to be popular on personal computers but has less market share of servers. UNIX operating systems, especially Linux, are the most popular on enterprise systems and servers but are also used on mobile devices and many other computer systems. On mobile devices, Symbian OS was dominant at first, being usurped by BlackBerry OS (introduced 2002) and iOS for iPhones (from 2007). Later on,

1805-442: A library with no protection between applications, such as eCos . A hypervisor is an operating system that runs a virtual machine . The virtual machine is unaware that it is an application and operates as if it had its own hardware. Virtual machines can be paused, saved, and resumed, making them useful for operating systems research, development, and debugging. They also enhance portability by enabling applications to be run on

1900-447: A malformed machine instruction . However, the most common error conditions are division by zero and accessing an invalid memory address . Users can send messages to the kernel to modify the behavior of a currently running process. For example, in the command-line environment , pressing the interrupt character (usually Control-C ) might terminate the currently running process. To generate software interrupts for x86 CPUs,

1995-415: A number of handheld devices such as smartphones and tablet computers, though the electronically similar SD card is better suited for those devices, due to their standardized form factor, which allows the card to be housed inside a device without protruding. A flash drive consists of a small printed circuit board carrying the circuit elements and a USB connector, insulated electrically and protected inside

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2090-455: A particular application's memory is stored, or even whether or not it has been allocated yet. In modern operating systems, memory which is accessed less frequently can be temporarily stored on a disk or other media to make that space available for use by other programs. This is called swapping , as an area of memory can be used by multiple programs, and what that memory area contains can be swapped or exchanged on demand. Virtual memory provides

2185-424: A plastic, metal, or rubberized case, which can be carried in a pocket or on a key chain, for example. Some are equipped with an I/O indication LED that lights up or blinks upon access. The USB connector may be protected by a removable cap or by retracting into the body of the drive, although it is not likely to be damaged if unprotected. Most flash drives use a standard type-A USB connection allowing connection with

2280-464: A port on a personal computer, but drives for other interfaces also exist (e.g. micro-USB and USB-C ports). USB flash drives draw power from the computer via the USB connection. Some devices combine the functionality of a portable media player with USB flash storage; they require a battery only when used to play music on the go. The basis for USB flash drives is flash memory , a type of floating-gate semiconductor memory invented by Fujio Masuoka in

2375-473: A possible inventor of the device. Given these competing inventor claims, patent disputes involving the USB flash drive have arisen over the years. Both Trek 2000 International and Netac Technology have accused others of infringing their patents on the USB flash drive. However, the question of who was the first to invent the USB flash drive has multiple claims persist, the Natec Technology get

2470-503: A program does not interfere with memory already in use by another program. Since programs time share, each program must have independent access to memory. Cooperative memory management, used by many early operating systems, assumes that all programs make voluntary use of the kernel 's memory manager, and do not exceed their allocated memory. This system of memory management is almost never seen any more, since programs often contain bugs which can cause them to exceed their allocated memory. If

2565-408: A program fails, it may cause memory used by one or more other programs to be affected or overwritten. Malicious programs or viruses may purposefully alter another program's memory, or may affect the operation of the operating system itself. With cooperative memory management, it takes only one misbehaved program to crash the system. Memory protection enables the kernel to limit a process' access to

2660-440: A program tries to access memory that is not accessible memory, but nonetheless has been allocated to it, the kernel is interrupted (see § Memory management ) . This kind of interrupt is typically a page fault . When the kernel detects a page fault it generally adjusts the virtual memory range of the program which triggered it, granting it access to the memory requested. This gives the kernel discretionary power over where

2755-470: A significant amount of CPU time. Direct memory access (DMA) is an architecture feature to allow devices to bypass the CPU and access main memory directly. (Separate from the architecture, a device may perform direct memory access to and from main memory either directly or via a bus.) When a computer user types a key on the keyboard, typically the character appears immediately on the screen. Likewise, when

2850-402: A specific moment in time. Hard real-time systems require exact timing and are common in manufacturing , avionics , military, and other similar uses. With soft real-time systems, the occasional missed event is acceptable; this category often includes audio or multimedia systems, as well as smartphones. In order for hard real-time systems be sufficiently exact in their timing, often they are just

2945-417: A user moves a mouse , the cursor immediately moves across the screen. Each keystroke and mouse movement generates an interrupt called Interrupt-driven I/O . An interrupt-driven I/O occurs when a process causes an interrupt for every character or word transmitted. Devices such as hard disk drives , solid-state drives , and magnetic tape drives can transfer data at a rate high enough that interrupting

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3040-453: A variation of the classic reader/writer problem . The writer receives a pipe from the shell for its output to be sent to the reader's input stream. The command-line syntax is alpha | bravo . alpha will write to the pipe when its computation is ready and then sleep in the wait queue. bravo will then be moved to the ready queue and soon will read from its input stream. The kernel will generate software interrupts to coordinate

3135-418: Is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web servers and supercomputers . In the personal computer market, as of September 2024 , Microsoft Windows holds a dominant market share of around 73%. macOS by Apple Inc. is in second place (15%), Linux is in third place (5%), and ChromeOS

3230-562: Is remote direct memory access , which enables each CPU to access memory belonging to other CPUs. Multicomputer operating systems often support remote procedure calls where a CPU can call a procedure on another CPU, or distributed shared memory , in which the operating system uses virtualization to generate shared memory that does not physically exist. A distributed system is a group of distinct, networked computers—each of which might have their own operating system and file system. Unlike multicomputers, they may be dispersed anywhere in

3325-484: Is a change away from the currently running process. Similarly, both hardware and software interrupts execute an interrupt service routine . Software interrupts may be normally occurring events. It is expected that a time slice will occur, so the kernel will have to perform a context switch . A computer program may set a timer to go off after a few seconds in case too much data causes an algorithm to take too long. Software interrupts may be error conditions, such as

3420-417: Is affected by the controller's firmware , internal data redundancy , and error correction algorithms. Until about 2005, most desktop and laptop computers were supplied with floppy disk drives in addition to USB ports, but floppy disk drives became obsolete after widespread adoption of USB ports and the larger USB drive capacity compared to the " 1.44 megabyte " 3.5-inch floppy disk. USB flash drives use

3515-401: Is also often used, which has up to 500 write cycles per physical sector, while some high-end flash drives have single-level cell (SLC) based memory that is good for around 30,000 writes. There is virtually no limit to the number of reads from such flash memory, so a well-worn USB drive may be write-protected to help ensure the life of individual cells. Estimation of flash memory endurance is

3610-422: Is difficult to define, but has been called "the layer of software that manages a computer's resources for its users and their applications ". Operating systems include the software that is always running, called a kernel —but can include other software as well. The two other types of programs that can run on a computer are system programs —which are associated with the operating system, but may not be part of

3705-452: Is downloaded and placed onto a FAT16 - or FAT32 -formatted USB flash drive connected to a system which is to be updated, and the path to the new firmware image is selected within the update component of system's firmware. Some motherboard manufacturers also allow such updates without the need to enter the system's firmware update component, making it possible to easily recover systems with corrupted firmware. In addition, HP has introduced

3800-896: Is in fourth place (2%). In the mobile sector (including smartphones and tablets ), as of September 2023 , Android's share is 68.92%, followed by Apple's iOS and iPadOS with 30.42%, and other operating systems with .66%. Linux distributions are dominant in the server and supercomputing sectors. Other specialized classes of operating systems (special-purpose operating systems), such as embedded and real-time systems, exist for many applications. Security-focused operating systems also exist. Some operating systems have low system requirements (e.g. light-weight Linux distribution ). Others may have higher system requirements. Some operating systems require installation or may come pre-installed with purchased computers ( OEM -installation), whereas others may run directly from media (i.e. live CD ) or flash memory (i.e. USB stick). An operating system

3895-484: Is not necessarily helpful to install one of these file systems. Sectors are 512 bytes long, for compatibility with hard disk drives, and the first sector can contain a master boot record and a partition table . Therefore, USB flash units can be partitioned just like hard disk drives. The memory in flash drives was commonly engineered with multi-level cell (MLC) based memory that is good for around 3,000-5,000 program-erase cycles. Nowadays Triple-level Cell (TLC)

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3990-443: Is only a single application running, at least conceptually, so there is no need to prevent interference between applications) and OS services are accessed via simple library calls (potentially inlining them based on compiler thresholds), without the usual overhead of context switches , in a way similarly to embedded and real-time OSes. Note that this overhead is not negligible: to the direct cost of mode switching it's necessary to add

4085-412: Is required not to alter in any way the information stored on the computer being examined. Other forensic suites run from CD-ROM or DVD-ROM , but cannot store data on the media they are run from (although they can write to other attached devices, such as external drives or memory sticks ). Motherboard firmware (including BIOS and UEFI ) can be updated using USB flash drives. Usually, new firmware

4180-499: Is supported by most UNIX systems. MINIX was a stripped-down version of UNIX, developed in 1987 for educational uses, that inspired the commercially available, free software Linux . Since 2008, MINIX is used in controllers of most Intel microchips , while Linux is widespread in data centers and Android smartphones. The invention of large scale integration enabled the production of personal computers (initially called microcomputers ) from around 1980. For around five years,

4275-568: Is supported in Windows 7 and Windows Vista (Service Pack 2 with a hotfix). A recent development for the use of a USB Flash Drive as an application carrier is to carry the Computer Online Forensic Evidence Extractor (COFEE) application developed by Microsoft . COFEE is a set of applications designed to search for and extract digital evidence on computers confiscated from suspects. Forensic software

4370-473: Is that they do not load user-installed software. Consequently, they do not need protection between different applications, enabling simpler designs. Very small operating systems might run in less than 10 kilobytes , and the smallest are for smart cards . Examples include Embedded Linux , QNX , VxWorks , and the extra-small systems RIOT and TinyOS . A real-time operating system is an operating system that guarantees to process events or data by or at

4465-435: Is the part of the operating system that provides protection between different applications and users. This protection is key to improving reliability by keeping errors isolated to one program, as well as security by limiting the power of malicious software and protecting private data, and ensuring that one program cannot monopolize the computer's resources. Most operating systems have two modes of operation: in user mode ,

4560-542: The CP/M (Control Program for Microcomputers) was the most popular operating system for microcomputers. Later, IBM bought the DOS (Disk Operating System) from Microsoft . After modifications requested by IBM, the resulting system was called MS-DOS (MicroSoft Disk Operating System) and was widely used on IBM microcomputers. Later versions increased their sophistication, in part by borrowing features from UNIX. Apple 's Macintosh

4655-529: The FAT32 , or exFAT file systems . The ubiquity of the FAT32 file system allows the drive to be accessed on virtually any host device with USB support. Also, standard FAT maintenance utilities (e.g., ScanDisk ) can be used to repair or retrieve corrupted data . However, because a flash drive appears as a USB-connected hard drive to the host system, the drive can be reformatted to any file system supported by

4750-504: The INT assembly language instruction is available. The syntax is INT X , where X is the offset number (in hexadecimal format) to the interrupt vector table . To generate software interrupts in Unix-like operating systems, the kill(pid,signum) system call will send a signal to another process. pid is the process identifier of the receiving process. signum is

4845-522: The USB mass storage device class standard, supported natively by modern operating systems such as Windows , Linux , macOS and other Unix-like systems, as well as many BIOS boot ROMs. USB drives with USB 2.0 support can store more data and transfer faster than much larger optical disc drives like CD-RW or DVD-RW drives and can be read by many other systems such as the Xbox One , PlayStation 4 , DVD players, automobile entertainment systems, and in

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4940-420: The transistor in the mid-1950s, mainframes began to be built. These still needed professional operators who manually do what a modern operating system would do, such as scheduling programs to run, but mainframes still had rudimentary operating systems such as Fortran Monitor System (FMS) and IBSYS . In the 1960s, IBM introduced the first series of intercompatible computers ( System/360 ). All of them ran

5035-410: The CPU for every byte or word transferred, and having the CPU transfer the byte or word between the device and memory, would require too much CPU time. Data is, instead, transferred between the device and memory independently of the CPU by hardware such as a channel or a direct memory access controller; an interrupt is delivered only when all the data is transferred. If a computer program executes

5130-474: The CPU to re-enter supervisor mode , placing the kernel in charge. This is called a segmentation violation or Seg-V for short, and since it is both difficult to assign a meaningful result to such an operation, and because it is usually a sign of a misbehaving program, the kernel generally resorts to terminating the offending program, and reports the error. Windows versions 3.1 through ME had some level of memory protection, but programs could easily circumvent

5225-725: The USB logo only if sold with a separate extension cable. Such cables are USB-compatible but do not conform to the USB standard. USB flash drives have been integrated into other commonly carried items, such as watches, pens, laser pointers, and even the Swiss Army Knife ; others have been fitted with novelty cases such as toy cars or Lego bricks. USB flash drives with images of dragons, cats or aliens are very popular in Asia. The small size, robustness and cheapness of USB flash drives make them an increasingly popular peripheral for case modding . Most flash drives ship preformatted with

5320-538: The application program, which then interacts with the user and with hardware devices. However, in some systems an application can request that the operating system execute another application within the same process, either as a subroutine or in a separate thread, e.g., the LINK and ATTACH facilities of OS/360 and successors . An interrupt (also known as an abort , exception , fault , signal , or trap ) provides an efficient way for most operating systems to react to

5415-629: The basic copyright of American in Dec 7, 2004. And in the lawsuit, the PNY company paid 1,000 million dollars to Natec. Flash drives are often measured by the rate at which they transfer data. Transfer rates may be given in megabytes per second (MB/s), megabits per second (Mbit/s), or in optical drive multipliers such as "180X" (180 times 150  KiB /s). File transfer rates vary considerably among devices. Second generation flash drives have claimed to read at up to 30 MB/s and write at about half that rate, which

5510-426: The clustered data), and the additional wear on flash drives may not be significant. Some file systems are designed to distribute usage over an entire memory device without concentrating usage on any part (e.g., for a directory) to prolong the life of simple flash memory devices. Some USB flash drives have this ' wear leveling ' feature built into the software controller to prolong device life, while others do not, so it

5605-453: The computer's memory. Various methods of memory protection exist, including memory segmentation and paging . All methods require some level of hardware support (such as the 80286 MMU), which does not exist in all computers. In both segmentation and paging, certain protected mode registers specify to the CPU what memory address it should allow a running program to access. Attempts to access other addresses trigger an interrupt, which causes

5700-471: The details of how interrupt service routines behave vary from operating system to operating system. However, several interrupt functions are common. The architecture and operating system must: A software interrupt is a message to a process that an event has occurred. This contrasts with a hardware interrupt — which is a message to the central processing unit (CPU) that an event has occurred. Software interrupts are similar to hardware interrupts — there

5795-691: The device more attractive for more applications. By reducing the probability of the device's premature failure, flash memory devices can now be considered for use where a magnetic disk would normally have been required. Flash drives have also experienced an exponential growth in their storage capacity over time (following the Moore's Law growth curve). As of 2013, single-packaged devices with capacities of 1  TB are readily available, and devices with 16 GB capacity are very economical. Storage capacities in this range have traditionally been considered to offer adequate space, because they allow enough space for both

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5890-488: The device's lifetime. Premature failure of a "live USB" could be circumvented by using a flash drive with a write-lock switch as a WORM device , identical to a live CD . Originally, this potential failure mode limited the use of "live USB" system to special-purpose applications or temporary tasks, such as: As of 2011 , newer flash memory designs have much higher estimated lifetimes. Several manufacturers are now offering warranties of 5 years or more. Such warranties should make

5985-481: The early 1980s. Flash memory uses floating-gate MOSFET transistors as memory cells . Multiple individuals have staked a claim to having invented the USB flash drive. On April 5, 1999, Amir Ban , Dov Moran , and Oron Ogdan of M-Systems , an Israeli company, filed a patent application entitled "Architecture for a Universal Serial Bus-Based PC Flash Disk". The patent was subsequently granted on November 14, 2000 and these individuals have often been recognized as

6080-405: The entire contents of the chip. Hardware designers later developed EEPROMs with the erasure region broken up into smaller "fields" that could be erased individually without affecting the others. Altering the contents of a particular memory location involved copying the entire field into an off-chip buffer memory, erasing the field, modifying the data as required in the buffer, and re-writing it into

6175-422: The environment. Interrupts cause the central processing unit (CPU) to have a control flow change away from the currently running program to an interrupt handler , also known as an interrupt service routine (ISR). An interrupt service routine may cause the central processing unit (CPU) to have a context switch . The details of how a computer processes an interrupt vary from architecture to architecture, and

6270-410: The hardware checks that the software is only executing legal instructions, whereas the kernel has unrestricted powers and is not subject to these checks. The kernel also manages memory for other processes and controls access to input/output devices. The operating system provides an interface between an application program and the computer hardware, so that an application program can interact with

6365-493: The hardware only by obeying rules and procedures programmed into the operating system. The operating system is also a set of services which simplify development and execution of application programs. Executing an application program typically involves the creation of a process by the operating system kernel , which assigns memory space and other resources, establishes a priority for the process in multi-tasking systems, loads program binary code into memory, and initiates execution of

6460-419: The host operating system. Flash drives can be defragmented . There is a widespread opinion that defragmenting brings little advantage (as there is no mechanical head that moves from fragment to fragment), and that defragmenting shortens the life of the drive by making many unnecessary writes. However, some sources claim that defragmenting a flash drive can improve performance (mostly due to improved caching of

6555-430: The host. Flash memory combines a number of older technologies, with lower cost, lower power consumption and small size made possible by advances in semiconductor device fabrication technology. The memory storage is based on earlier EPROM and EEPROM technologies. These had limited capacity, were slow for both reading and writing, required complex high-voltage drive circuitry, and could be re-written only after erasing

6650-418: The indirect pollution of important processor structures (like CPU caches , the instruction pipeline , and so on) which affects both user-mode and kernel-mode performance. The first computers in the late 1940s and 1950s were directly programmed either with plugboards or with machine code inputted on media such as punch cards , without programming languages or operating systems. After the introduction of

6745-404: The interrupt request, the operating system will: When the writing process has its time slice expired, the operating system will: With the program counter now reset, the interrupted process will resume its time slice. Among other things, a multiprogramming operating system kernel must be responsible for managing all system memory which is currently in use by the programs. This ensures that

6840-448: The inventors of the USB flash drive. Also in 1999, Shimon Shmueli , an engineer at IBM, submitted an invention disclosure asserting that he had invented the USB flash drive. A Singaporean company named Trek 2000 International is the first company known to have sold a USB flash drive, and has also maintained that it is the original inventor of the device. Finally Pua Khein-Seng , a Malaysian engineer, has also been recognized by some as

6935-431: The kernel—and applications—all other software. There are three main purposes that an operating system fulfills: With multiprocessors multiple CPUs share memory. A multicomputer or cluster computer has multiple CPUs, each of which has its own memory . Multicomputers were developed because large multiprocessors are difficult to engineer and prohibitively expensive; they are universal in cloud computing because of

7030-400: The memory allocated to a different one. Around the same time, teleprinters began to be used as terminals so multiple users could access the computer simultaneously. The operating system MULTICS was intended to allow hundreds of users to access a large computer. Despite its limited adoption, it can be considered the precursor to cloud computing . The UNIX operating system originated as

7125-448: The memory chips than parallel access , simplifying the manufacture of multi- gigabyte drives. Computers access modern flash memory systems very much like hard disk drives, where the controller system has full control over where information is actually stored. The actual EEPROM writing and erasure processes are, however, still very similar to the earlier systems described above. Many low-cost MP3 players simply add extra software and

7220-408: The need to use it. A general protection fault would be produced, indicating a segmentation violation had occurred; however, the system would often crash anyway. The use of virtual memory addressing (such as paging or segmentation) means that the kernel can choose what memory each program may use at any given time, allowing the operating system to use the same memory locations for multiple tasks. If

7315-419: The norm as data security needs increase; on-the-fly encryption systems are particularly useful in this regard, as they can transparently encrypt large amounts of data. In some cases, a secure USB drive may use a hardware-based encryption mechanism that uses a hardware module instead of software for strongly encrypting data. IEEE 1667 is an attempt to create a generic authentication platform for USB drives. It

7410-408: The open-source Android operating system (introduced 2008), with a Linux kernel and a C library ( Bionic ) partially based on BSD code, became most popular. The components of an operating system are designed to ensure that various parts of a computer function cohesively. With the de facto obsoletion of DOS , all user software must interact with the operating system to access hardware. The kernel

7505-493: The operating system software and some free space for the user's data. Installers of some operating systems can be stored to a flash drive instead of a CD or DVD, including various Linux distributions , Windows 7 and newer versions, and macOS . In particular, Mac OS X 10.7 is distributed only online, through the Mac App Store , or on flash drives; for a MacBook Air with Boot Camp and no external optical drive,

7600-421: The piping. Signals may be classified into 7 categories. The categories are: Input/output (I/O) devices are slower than the CPU. Therefore, it would slow down the computer if the CPU had to wait for each I/O to finish. Instead, a computer may implement interrupts for I/O completion, avoiding the need for polling or busy waiting. Some computers require an interrupt for each character or word, costing

7695-506: The programmer or the user with the perception that there is a much larger amount of RAM in the computer than is really there. USB flash drive A flash drive (also thumb drive , memory stick , and pen drive / pendrive ) is a data storage device that includes flash memory with an integrated USB interface. A typical USB drive is removable, rewritable, and smaller than an optical disc , and usually weighs less than 30 g (1 oz). Since first offered for sale in late 2000,

7790-461: The protocol overhead that translates to a 35  MB /s effective throughput. That same year, Intel sparked widespread use of second generation USB by including them within its laptops. By 2010, the maximum available storage capacity for the devices had reached upwards of 128 GB. USB 3.0 was slow to appear in laptops. Through 2010, the majority of laptop models still contained only USB 2.0. In January 2013, tech company Kingston, released

7885-572: The same field. This required considerable computer support, and PC-based EEPROM flash memory systems often carried their own dedicated microprocessor system. Flash drives are more or less a miniaturized version of this. The development of high-speed serial data interfaces such as USB made semiconductor memory systems with serially accessed storage viable, and the simultaneous development of small, high-speed, low-power microprocessor systems allowed this to be incorporated into extremely compact systems. Serial access requires far fewer electrical connections for

7980-418: The same operating system— OS/360 —which consisted of millions of lines of assembly language that had thousands of bugs . The OS/360 also was the first popular operating system to support multiprogramming , such that the CPU could be put to use on one job while another was waiting on input/output (I/O). Holding multiple jobs in memory necessitated memory partitioning and safeguards against one job accessing

8075-400: The signal number (in mnemonic format) to be sent. (The abrasive name of kill was chosen because early implementations only terminated the process.) In Unix-like operating systems, signals inform processes of the occurrence of asynchronous events. To communicate asynchronously, interrupts are required. One reason a process needs to asynchronously communicate to another process solves

8170-400: The size of the machine needed. The different CPUs often need to send and receive messages to each other; to ensure good performance, the operating systems for these machines need to minimize this copying of packets . Newer systems are often multiqueue —separating groups of users into separate queues —to reduce the need for packet copying and support more concurrent users. Another technique

8265-578: The slowest of three factors: the USB version used, the speed in which the USB controller device can read and write data onto the flash memory, and the speed of the hardware bus , especially in the case of add-on USB ports. USB flash drives usually specify their read and write speeds in megabytes per second (MB/s); read speed is usually faster. These speeds are for optimal conditions; real-world speeds are usually slower. In particular, circumstances that often lead to speeds much lower than advertised are transfer (particularly writing) of many small files rather than

8360-445: The smallest size, with the biggest memory, offering drives only a few millimeters larger than the USB plug itself, some manufacturers differentiate their products by using elaborate housings, which are often bulky and make the drive difficult to connect to the USB port. Because the USB port connectors on a computer housing are often closely spaced, plugging a flash drive into a USB port may block an adjacent port. Such devices may carry

8455-657: The storage capacities of USB drives range from 8 megabytes to 256 gigabytes (GB ), 512 GB and 1  terabyte (TB ). As of 2023, 2 TB flash drives were the largest currently in production. Some allow up to 100,000 write/erase cycles, depending on the exact type of memory chip used, and are thought to physically last between 10 and 100 years under normal circumstances ( shelf storage time ). Common uses of USB flash drives are for storage, supplementary back-ups , and transferring of computer files . Compared with floppy disks or CDs , they are smaller, faster, have significantly more capacity, and are more durable due to

8550-442: The system and may also include accounting software for cost allocation of processor time , mass storage , peripherals, and other resources. For hardware functions such as input and output and memory allocation , the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or

8645-473: The world. Middleware , an additional software layer between the operating system and applications, is often used to improve consistency. Although it functions similarly to an operating system, it is not a true operating system. Embedded operating systems are designed to be used in embedded computer systems , whether they are internet of things objects or not connected to a network. Embedded systems include many household appliances. The distinguishing factor

8740-601: Was 8 MB/s. These differences differ radically from one drive to another; some could write small files 10% faster than for large ones. The examples given are chosen to illustrate extremes. The most common use of flash drives is to transport and store personal files, such as documents, pictures and videos. Individuals also store medical information on flash drives for emergencies and disaster preparation. With wide deployment of flash drives in various environments (secured or otherwise), data and information security remain critical issues. Biometrics and encryption are becoming

8835-424: Was about 20 times faster than the theoretical transfer rate achievable by the previous model, USB 1.1, which is limited to 12 Mbit/s (1.5 MB/s) with accounted overhead. The effective transfer rate of a device is significantly affected by the data access pattern. By 2002, USB flash drives had USB 2.0 connectivity, which has 480  Mbit /s as the transfer rate upper bound; after accounting for

8930-480: Was started, and in early 1997, WorkGroup Solutions , Yggdrasil , Linux Journal , Linux International , and Torvalds appealed the original trademark assignment as "fraudulent and obtained under false pretenses". By November, the case was settled and Torvalds owned the trademark. LMI originally charged a nominal sublicensing fee for use of the Linux name as part of trademarks, but later changed this in favor of offering

9025-406: Was the first popular computer to use a graphical user interface (GUI). The GUI proved much more user friendly than the text-only command-line interface earlier operating systems had used. Following the success of Macintosh, MS-DOS was updated with a GUI overlay called Windows . Windows later was rewritten as a stand-alone operating system, borrowing so many features from another ( VAX VMS ) that

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