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60-508: The architectural work on the ROMP began in late spring of 1977, as a spin-off of IBM Research 's 801 RISC processor (hence the "Research" in the acronym). Most of the architectural changes were for cost reduction, such as adding 16-bit instructions for byte-efficiency. The original ROMP had a 24-bit architecture, but the instruction set was changed to 32 bits a few years into the development. The first chips were ready in early 1981, making ROMP

120-513: A ceramic substrate with pins arranged in an array. An organic pin grid array (OPGA) is a type of connection for integrated circuits , and especially CPUs , where the silicon die is attached to a plate made out of an organic plastic which is pierced by an array of pins which make the requisite connections to the socket . Plastic pin grid array (PPGA) packaging was used by Intel for late-model Mendocino core Celeron processors based on Socket 370 . Some pre-Socket 8 processors also used

180-493: A translation lookaside buffer , and a store buffer. The ROMP and Rosetta were originally implemented in an IBM 2   μm silicon-gate NMOS technology with two levels of metal interconnect. The ROMP consists of 45,000 transistors and is 7.65   ×   7.65   mm large (58.52   mm), while Rosetta consists of 61,500 transistors and is 9.02   ×   9.02   mm large (81.36   mm). Both are packaged in 135-pin ceramic pin grid arrays . A CMOS version of

240-505: A basic ALU operation, such as "add", with the access of one or more operands in memory (using addressing modes such as direct, indirect, indexed, etc.). Certain architectures may allow two or three operands (including the result) directly in memory or may be able to perform functions such as automatic pointer increment, etc. Software-implemented instruction sets may have even more complex and powerful instructions. Reduced instruction-set computers , RISC , were first widely implemented during

300-401: A cache line or virtual memory page boundary, for instance), and are therefore somewhat easier to optimize for speed. In early 1960s computers, main memory was expensive and very limited, even on mainframes. Minimizing the size of a program to make sure it would fit in the limited memory was often central. Thus the size of the instructions needed to perform a particular task, the code density ,

360-415: A conditional branch instruction will transfer control if the condition is true, so that execution proceeds to a different part of the program, and not transfer control if the condition is false, so that execution continues sequentially. Some instruction sets also have conditional moves, so that the move will be executed, and the data stored in the target location, if the condition is true, and not executed, and

420-416: A fashion that does not depend on the characteristics of that implementation, providing binary compatibility between implementations. This enables multiple implementations of an ISA that differ in characteristics such as performance , physical size, and monetary cost (among other things), but that are capable of running the same machine code, so that a lower-performance, lower-cost machine can be replaced with

480-572: A given instruction may specify: More complex operations are built up by combining these simple instructions, which are executed sequentially, or as otherwise directed by control flow instructions. Examples of operations common to many instruction sets include: Processors may include "complex" instructions in their instruction set. A single "complex" instruction does something that may take many instructions on other computers. Such instructions are typified by instructions that take multiple steps, control multiple functional units, or otherwise appear on

540-408: A higher-cost, higher-performance machine without having to replace software. It also enables the evolution of the microarchitectures of the implementations of that ISA, so that a newer, higher-performance implementation of an ISA can run software that runs on previous generations of implementations. If an operating system maintains a standard and compatible application binary interface (ABI) for

600-516: A larger word size (32 bits instead of 24), and the inclusion of virtual memory . The architecture supported 8-, 16-, and 32-bit integers, 32-bit addressing, and a 40-bit virtual address space . It had an instruction pointer register and sixteen 32-bit general-purpose registers . The microprocessor was controlled by 118 simple 16- and 32-bit instructions. The ROMP's virtual memory has a segmented 40-bit (1   TB) address space consisting of 4,096 256   MB segments. The 40-bit virtual address

660-601: A larger scale than the bulk of simple instructions implemented by the given processor. Some examples of "complex" instructions include: Complex instructions are more common in CISC instruction sets than in RISC instruction sets, but RISC instruction sets may include them as well. RISC instruction sets generally do not include ALU operations with memory operands, or instructions to move large blocks of memory, but most RISC instruction sets include SIMD or vector instructions that perform

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720-517: A particular ISA, machine code will run on future implementations of that ISA and operating system. However, if an ISA supports running multiple operating systems, it does not guarantee that machine code for one operating system will run on another operating system, unless the first operating system supports running machine code built for the other operating system. An ISA can be extended by adding instructions or other capabilities, or adding support for larger addresses and data values; an implementation of

780-419: A period of rapidly growing memory subsystems. They sacrifice code density to simplify implementation circuitry, and try to increase performance via higher clock frequencies and more registers. A single RISC instruction typically performs only a single operation, such as an "add" of registers or a "load" from a memory location into a register. A RISC instruction set normally has a fixed instruction length , whereas

840-517: A series of five processors spanning a wide range of cost and performance. None of the five engineering design teams could count on being able to bring about adjustments in architectural specifications as a way of easing difficulties in achieving cost and performance objectives. Some virtual machines that support bytecode as their ISA such as Smalltalk , the Java virtual machine , and Microsoft 's Common Language Runtime , implement this by translating

900-399: A similar form factor, although they were not officially referred to as PPGA. The staggered pin grid array (SPGA) is used by Intel processors based on Socket 5 and Socket 7 . Socket 8 used a partial SPGA layout on half the processor. It consists of two square arrays of pins, offset in both directions by half the minimum distance between pins in one of the arrays. Put differently: within

960-545: A single instruction. Some exotic instruction sets do not have an opcode field, such as transport triggered architectures (TTA), only operand(s). Most stack machines have " 0-operand " instruction sets in which arithmetic and logical operations lack any operand specifier fields; only instructions that push operands onto the evaluation stack or that pop operands from the stack into variables have operand specifiers. The instruction set carries out most ALU actions with postfix ( reverse Polish notation ) operations that work only on

1020-440: A square boundary the pins form a diagonal square lattice . There is generally a section in the center of the package without any pins. SPGA packages are usually used by devices that require a higher pin density than what a PGA can provide, such as microprocessors . A stud grid array (SGA) is a short-pinned pin grid array chip scale package for use in surface-mount technology . The polymer stud grid array or plastic stud grid array

1080-463: A typical CISC instruction set has instructions of widely varying length. However, as RISC computers normally require more and often longer instructions to implement a given task, they inherently make less optimal use of bus bandwidth and cache memories. Certain embedded RISC ISAs like Thumb and AVR32 typically exhibit very high density owing to a technique called code compression. This technique packs two 16-bit instructions into one 32-bit word, which

1140-540: A writable control store use it to allow the instruction set to be changed (for example, the Rekursiv processor and the Imsys Cjip ). CPUs designed for reconfigurable computing may use field-programmable gate arrays (FPGAs). An ISA can also be emulated in software by an interpreter . Naturally, due to the interpretation overhead, this is slower than directly running programs on the emulated hardware, unless

1200-415: Is 15 bytes (120 bits). Within an instruction set, different instructions may have different lengths. In some architectures, notably most reduced instruction set computers (RISC), instructions are a fixed length , typically corresponding with that architecture's word size . In other architectures, instructions have variable length , typically integral multiples of a byte or a halfword . Some, such as

1260-444: Is a complex issue. There were two stages in history for the microprocessor. The first was the CISC (Complex Instruction Set Computer), which had many different instructions. In the 1970s, however, places like IBM did research and found that many instructions in the set could be eliminated. The result was the RISC (Reduced Instruction Set Computer), an architecture that uses a smaller set of instructions. A simpler instruction set may offer

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1320-553: Is a form of pin grid array in which the die faces downwards on the top of the substrate with the back of the die exposed. This allows the die to have a more direct contact with the heatsink or other cooling mechanism. FC-PGA CPUs were introduced by Intel in 1999, for Coppermine core Pentium III and Celeron processors based on Socket 370 , and were produced until Socket G3 in 2013. FC-PGA processors fit into zero insertion force (ZIF) motherboard sockets ; similar packages were also used by AMD. A ceramic pin grid array (CPGA)

1380-625: Is a type of packaging used by integrated circuits . This type of packaging uses a ceramic substrate with pins arranged in a pin grid array. Some CPUs that use CPGA packaging are the AMD Socket A Athlons and the Duron . A CPGA was used by AMD for Athlon and Duron processors based on Socket A, as well as some AMD processors based on Socket AM2 and Socket AM2+ . While similar form factors have been used by other manufacturers, they are not officially referred to as CPGA. This type of packaging uses

1440-476: Is called an implementation of that ISA. In general, an ISA defines the supported instructions , data types , registers , the hardware support for managing main memory , fundamental features (such as the memory consistency , addressing modes , virtual memory ), and the input/output model of implementations of the ISA. An ISA specifies the behavior of machine code running on implementations of that ISA in

1500-602: Is due to the many addressing modes and optimizations (such as sub-register addressing, memory operands in ALU instructions, absolute addressing, PC-relative addressing, and register-to-register spills) that CISC ISAs offer. The size or length of an instruction varies widely, from as little as four bits in some microcontrollers to many hundreds of bits in some VLIW systems. Processors used in personal computers , mainframes , and supercomputers have minimum instruction sizes between 8 and 64 bits. The longest possible instruction on x86

1560-471: Is formed in the MMU by concatenating a 12-bit segment identifier with 28 low-order bits from a 32-bit ROMP-computed virtual address. The segment identifier is obtained from a set of 16 segment identifiers stored in the MMU, addressed by the four high-order bits of the 32-bit ROMP-computed virtual address. The ROMP is a scalar processor with a three-stage pipeline. In the first stage, if there are instructions in

1620-553: Is similar to the code density of RISC; the increased instruction density is offset by requiring more of the primitive instructions to do a task. There has been research into executable compression as a mechanism for improving code density. The mathematics of Kolmogorov complexity describes the challenges and limits of this. In practice, code density is also dependent on the compiler . Most optimizing compilers have options that control whether to optimize code generation for execution speed or for code density. For instance GCC has

1680-538: Is the set of processor design techniques used, in a particular processor, to implement the instruction set. Processors with different microarchitectures can share a common instruction set. For example, the Intel Pentium and the AMD Athlon implement nearly identical versions of the x86 instruction set , but they have radically different internal designs. The concept of an architecture , distinct from

1740-432: Is then unpacked at the decode stage and executed as two instructions. Minimal instruction set computers (MISC) are commonly a form of stack machine , where there are few separate instructions (8–32), so that multiple instructions can be fit into a single machine word. These types of cores often take little silicon to implement, so they can be easily realized in an FPGA or in a multi-core form. The code density of MISC

1800-504: The ARM with Thumb-extension have mixed variable encoding, that is two fixed, usually 32-bit and 16-bit encodings, where instructions cannot be mixed freely but must be switched between on a branch (or exception boundary in ARMv8). Fixed-length instructions are less complicated to handle than variable-length instructions for several reasons (not having to check whether an instruction straddles

1860-411: The compiler responsible for instruction issue and scheduling. Architectures with even less complexity have been studied, such as the minimal instruction set computer (MISC) and one-instruction set computer (OISC). These are theoretically important types, but have not been commercialized. Machine language is built up from discrete statements or instructions . On the processing architecture,

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1920-399: The instruction pipeline only allow a single memory load or memory store per instruction, leading to a load–store architecture (RISC). For another example, some early ways of implementing the instruction pipeline led to a delay slot . Ceramic pin grid array A pin grid array ( PGA ) is a type of integrated circuit packaging . In a PGA, the package is square or rectangular, and

1980-529: The microarchitecture of a processor, engineers use blocks of "hard-wired" electronic circuitry (often designed separately) such as adders, multiplexers, counters, registers, ALUs, etc. Some kind of register transfer language is then often used to describe the decoding and sequencing of each instruction of an ISA using this physical microarchitecture. There are two basic ways to build a control unit to implement this description (although many designs use middle ways or compromises): Some microcoded CPU designs with

2040-457: The stack or in an implicit register. If some of the operands are given implicitly, fewer operands need be specified in the instruction. When a "destination operand" explicitly specifies the destination, an additional operand must be supplied. Consequently, the number of operands encoded in an instruction may differ from the mathematically necessary number of arguments for a logical or arithmetic operation (the arity ). Operands are either encoded in

2100-431: The "opcode" representation of the instruction, or else are given as values or addresses following the opcode. Register pressure measures the availability of free registers at any point in time during the program execution. Register pressure is high when a large number of the available registers are in use; thus, the higher the register pressure, the more often the register contents must be spilled into memory. Increasing

2160-425: The 16-byte instruction prefetch buffer, an instruction was fetched, decoded, and operands from the general-purpose register file read. The instruction prefetch buffer read a 32-bit word from the memory whenever the ROMP was not accessing it. Instructions were executed in the second stage, and written back into the general-purpose register file in the third stage. The ROMP used a bypass network and appropriately scheduled

2220-457: The ROMP and Rosetta (called ROMP-C and Rosetta-C) was later developed. Instruction set architecture In computer science , an instruction set architecture ( ISA ) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, such as a central processing unit (CPU),

2280-563: The RT PC was caused by overly ambitious software plans for the RT PC and its operating system (OS). This OS virtualized the hardware and could host multiple other operating systems. This technology, called virtualization , while commonplace in mainframe systems, only began to gain traction in smaller systems in the 21st century. An improved CMOS version of the ROMP was first used in the IBM 6152 Academic System workstation, and later in some models of

2340-555: The RT PC. IBM Research used the ROMP in its Research Parallel Processor Prototype (RP3), an early experimental scalable shared-memory multiprocessor that supported up to 512 processors first detailed in 1985; and the CMOS version in its ACE, an experimental NUMA multiprocessor that was operational in 1988. The ROMP's architecture was based on the original version of the IBM Research 801 minicomputer . The main differences were

2400-595: The bytecode for commonly used code paths into native machine code. In addition, these virtual machines execute less frequently used code paths by interpretation (see: Just-in-time compilation ). Transmeta implemented the x86 instruction set atop VLIW processors in this fashion. An ISA may be classified in a number of different ways. A common classification is by architectural complexity . A complex instruction set computer (CISC) has many specialized instructions, some of which may only be rarely used in practical programs. A reduced instruction set computer (RISC) simplifies

2460-400: The design of a specific machine, was developed by Fred Brooks at IBM during the design phase of System/360 . Prior to NPL [System/360], the company's computer designers had been free to honor cost objectives not only by selecting technologies but also by fashioning functional and architectural refinements. The SPREAD compatibility objective, in contrast, postulated a single architecture for

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2520-406: The expression stack , not on data registers or arbitrary main memory cells. This can be very convenient for compiling high-level languages, because most arithmetic expressions can be easily translated into postfix notation. Conditional instructions often have a predicate field—a few bits that encode the specific condition to cause an operation to be performed rather than not performed. For example,

2580-410: The extended ISA will still be able to execute machine code for versions of the ISA without those extensions. Machine code using those extensions will only run on implementations that support those extensions. The binary compatibility that they provide makes ISAs one of the most fundamental abstractions in computing . An instruction set architecture is distinguished from a microarchitecture , which

2640-574: The first industrial RISC. The processor was revealed at the International Solid-State Circuits Conference in 1984 ROMP first appeared in a commercial product as the processor for the IBM RT PC workstation , which was introduced in 1986. To provide examples for RT PC production, volume production of the ROMP and its MMU began in 1985. The delay between the completion of the ROMP design, and introduction of

2700-414: The hardware running the emulator is an order of magnitude faster. Today, it is common practice for vendors of new ISAs or microarchitectures to make software emulators available to software developers before the hardware implementation is ready. Often the details of the implementation have a strong influence on the particular instructions selected for the instruction set. For example, many implementations of

2760-546: The instruction set includes support for something such as " fetch-and-add ", " load-link/store-conditional " (LL/SC), or "atomic compare-and-swap ". A given instruction set can be implemented in a variety of ways. All ways of implementing a particular instruction set provide the same programming model , and all implementations of that instruction set are able to run the same executables. The various ways of implementing an instruction set give different tradeoffs between cost, performance, power consumption, size, etc. When designing

2820-663: The large number of bits needed to encode the three registers of a 3-operand instruction, RISC architectures that have 16-bit instructions are invariably 2-operand designs, such as the Atmel AVR, TI MSP430 , and some versions of ARM Thumb . RISC architectures that have 32-bit instructions are usually 3-operand designs, such as the ARM , AVR32 , MIPS , Power ISA , and SPARC architectures. Each instruction specifies some number of operands (registers, memory locations, or immediate values) explicitly . Some instructions give one or both operands implicitly, such as by being stored on top of

2880-401: The number of registers in an architecture decreases register pressure but increases the cost. While embedded instruction sets such as Thumb suffer from extremely high register pressure because they have small register sets, general-purpose RISC ISAs like MIPS and Alpha enjoy low register pressure. CISC ISAs like x86-64 offer low register pressure despite having smaller register sets. This

2940-439: The operation to perform, such as add contents of memory to register —and zero or more operand specifiers, which may specify registers , memory locations, or literal data. The operand specifiers may have addressing modes determining their meaning or may be in fixed fields. In very long instruction word (VLIW) architectures, which include many microcode architectures, multiple simultaneous opcodes and operands are specified in

3000-447: The option -Os to optimize for small machine code size, and -O3 to optimize for execution speed at the cost of larger machine code. The instructions constituting a program are rarely specified using their internal, numeric form ( machine code ); they may be specified by programmers using an assembly language or, more commonly, may be generated from high-level programming languages by compilers . The design of instruction sets

3060-449: The pins are arranged in a regular array on the underside of the package. The pins are commonly spaced 2.54 mm (0.1") apart, and may or may not cover the entire underside of the package. PGAs are often mounted on printed circuit boards using the through hole method or inserted into a socket . PGAs allow for more pins per integrated circuit than older packages, such as dual in-line package (DIP). The chip can be mounted either on

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3120-476: The potential for higher speeds, reduced processor size, and reduced power consumption. However, a more complex set may optimize common operations, improve memory and cache efficiency, or simplify programming. Some instruction set designers reserve one or more opcodes for some kind of system call or software interrupt . For example, MOS Technology 6502 uses 00 H , Zilog Z80 uses the eight codes C7,CF,D7,DF,E7,EF,F7,FF H while Motorola 68000 use codes in

3180-570: The processor by efficiently implementing only the instructions that are frequently used in programs, while the less common operations are implemented as subroutines, having their resulting additional processor execution time offset by infrequent use. Other types include very long instruction word (VLIW) architectures, and the closely related long instruction word (LIW) and explicitly parallel instruction computing (EPIC) architectures. These architectures seek to exploit instruction-level parallelism with less hardware than RISC and CISC by making

3240-479: The range A000..AFFF H . Fast virtual machines are much easier to implement if an instruction set meets the Popek and Goldberg virtualization requirements . The NOP slide used in immunity-aware programming is much easier to implement if the "unprogrammed" state of the memory is interpreted as a NOP . On systems with multiple processors, non-blocking synchronization algorithms are much easier to implement if

3300-436: The register file reads and writes to support back-to-back execution of dependent instructions. Most register-to-register instructions were executed in one cycle; of the 118 instructions, 84 had a single-cycle latency. The ROMP had an IBM-developed companion integrated circuit which was code-named Rosetta during development. Rosetta was a memory management unit (MMU), and it provided the ROMP with address translation facilities,

3360-488: The same arithmetic operation on multiple pieces of data at the same time. SIMD instructions have the ability of manipulating large vectors and matrices in minimal time. SIMD instructions allow easy parallelization of algorithms commonly involved in sound, image, and video processing. Various SIMD implementations have been brought to market under trade names such as MMX , 3DNow! , and AltiVec . On traditional architectures, an instruction includes an opcode that specifies

3420-524: The target location not modified, if the condition is false. Similarly, IBM z/Architecture has a conditional store instruction. A few instruction sets include a predicate field in every instruction; this is called branch predication . Instruction sets may be categorized by the maximum number of operands explicitly specified in instructions. (In the examples that follow, a , b , and c are (direct or calculated) addresses referring to memory cells, while reg1 and so on refer to machine registers.) Due to

3480-472: The top or the bottom (the pinned side). Connections can be made either by wire bonding or through flip chip mounting. Typically, PGA packages use wire bonding when the chip is mounted on the pinned side, and flip chip construction when the chip is on the top side. Some PGA packages contain multiple dies, for example Zen 2 and Zen 3 Ryzen CPUs for the AM4 socket . A flip-chip pin grid array (FC-PGA or FCPGA)

3540-753: Was an important characteristic of any instruction set. It remained important on the initially-tiny memories of minicomputers and then microprocessors. Density remains important today, for smartphone applications, applications downloaded into browsers over slow Internet connections, and in ROMs for embedded applications. A more general advantage of increased density is improved effectiveness of caches and instruction prefetch. Computers with high code density often have complex instructions for procedure entry, parameterized returns, loops, etc. (therefore retroactively named Complex Instruction Set Computers , CISC ). However, more typical, or frequent, "CISC" instructions merely combine

3600-497: Was developed jointly by the Interuniversity Microelectronics Centre (IMEC) and Laboratory for Production Technology , Siemens AG . The reduced pin grid array was used by the socketed mobile variants of Intel's Core i3/5/7 processors and features a reduced pin pitch of 1   mm, as opposed to the 1.27   mm pin pitch used by contemporary AMD processors and older Intel processors. It

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