Microprocessor

A microprocessor is a general-purpose entity. Several specialized processing devices have followed:

• A digital signal processor (DSP) is specialized for signal processing.
• Graphics processing units (GPUs) are processors designed primarily for realtime rendering of images.
• Other specialized units exist for video processing and machine vision. (See: Hardware acceleration.)
• Microcontrollers integrate a microprocessor with peripheral devices in embedded systems.
• Systems on chip (SoCs) often integrate one or more microprocessor or microcontroller cores with other components such as radio modems, and are used in smartphones and tablet computers.

Microprocessors can be selected for differing applications based on their word size, which is a measure of their complexity. Longer word sizes allow each clock cycle of a processor to carry out more computation, but correspond to physically larger integrated circuit dies with higher standby and operating power consumption.[1] 4-, 8- or 12-bit processors are widely integrated into microcontrollers operating embedded systems. Where a system is expected to handle larger volumes of data or require a more flexible user interface, 16-, 32- or 64-bit processors are used. An 8- or 16-bit processor may be selected over a 32-bit processor for system on a chip or microcontroller applications that require extremely low-power electronics, or are part of a mixed-signal integrated circuit with noise-sensitive on-chip analog electronics such as high-resolution analog to digital converters, or both. Running 32-bit arithmetic on an 8-bit chip could end up using more power, as the chip must execute software with multiple instructions.[2]

These projects delivered a microprocessor at about the same time: Garrett AiResearch's Central Air Data Computer (CADC) (1970), Texas Instruments' TMS 1802NC (September 1971) and Intel's 4004 (November 1971, based on an earlier 1969 Busicom design). Arguably, Four-Phase Systems AL1 microprocessor was also delivered in 1969.

In 1968, Garrett AiResearch (who employed designers Ray Holt and Steve Geller) was invited to produce a digital computer to compete with electromechanical systems then under development for the main flight control computer in the US Navy's new F-14 Tomcat fighter. The design was complete by 1970, and used a MOS-based chipset as the core CPU. The design was significantly (approximately 20 times) smaller and much more reliable than the mechanical systems it competed against, and was used in all of the early Tomcat models. This system contained "a 20-bit, pipelined, parallel multi-microprocessor". The Navy refused to allow publication of the design until 1997. Released in 1998, the documentation on the CADC, and the MP944 chipset, are well known. Ray Holt's autobiographical story of this design and development is presented in the book: The Accidental Engineer.[11][12]

Ray Holt graduated from California Polytechnic University in 1968, and began his computer design career with the CADC. From its inception, it was shrouded in secrecy until 1998 when at Holt's request, the US Navy allowed the documents into the public domain. Holt has claimed that no-one has compared this microprocessor with those that came later.[13] According to Parab et al. (2007),

The scientific papers and literature published around 1971 reveal that the MP944 digital processor used for the F-14 Tomcat aircraft of the US Navy qualifies as the first microprocessor. Although interesting, it was not a single-chip processor, as was not the Intel 4004 – they both were more like a set of parallel building blocks you could use to make a general-purpose form. It contains a CPU, RAM, ROM, and two other support chips like the Intel 4004. It was made from the same P-channel technology, operated at military specifications and had larger chips – an excellent computer engineering design by any standards. Its design indicates a major advance over Intel, and two year earlier. It actually worked and was flying in the F-14 when the Intel 4004 was announced. It indicates that today's industry theme of converging DSP-microcontroller architectures was started in 1971.[14]

This convergence of DSP and microcontroller architectures is known as a digital signal controller.[15]

The Four-Phase Systems AL1 was an 8-bit bit slice chip containing eight registers and an ALU.[16] It was designed by Lee Boysel in 1969.[17][18][19] At the time, it formed part of a nine-chip, 24-bit CPU with three AL1s, but it was later called a microprocessor when, in response to 1990s litigation by Texas Instruments, a demonstration system was constructed where a single AL1 formed part of a courtroom demonstration computer system, together with RAM, ROM, and an input-output device.[20]

The PICO1/GI250 chip introduced in 1971: It was designed by Pico Electronics (Glenrothes, Scotland) and manufactured by General Instrument of Hicksville NY.

In 1971, Pico Electronics[21] and General Instrument (GI) introduced their first collaboration in ICs, a complete single chip calculator IC for the Monroe/Litton Royal Digital III calculator. This chip could also arguably lay claim to be one of the first microprocessors or microcontrollers having ROM, RAM and a RISC instruction set on-chip. The layout for the four layers of the PMOS process was hand drawn at x500 scale on mylar film, a significant task at the time given the complexity of the chip.

Pico was a spinout by five GI design engineers whose vision was to create single chip calculator ICs. They had significant previous design experience on multiple calculator chipsets with both GI and Marconi-Elliott.[22] The key team members had originally been tasked by Elliott Automation to create an 8-bit computer in MOS and had helped establish a MOS Research Laboratory in Glenrothes, Scotland in 1967.

Calculators were becoming the largest single market for semiconductors so Pico and GI went on to have significant success in this burgeoning market. GI continued to innovate in microprocessors and microcontrollers with products including the CP1600, IOB1680 and PIC1650.[23] In 1987, the GI Microelectronics business was spun out into the Microchip PIC microcontroller business.

The 4004 with cover removed (left) and as actually used (right)

The Intel 4004 is generally regarded as the first true microprocessor built on a single chip,[24][25] priced at US$60 (equivalent to $378.78 in 2019)[26] The first known advertisement for the 4004 is dated November 15, 1971 and appeared in Electronic News. The microprocessor was designed by a team consisting of Italian engineer Federico Faggin, American engineers Marcian Hoff and Stanley Mazor, and Japanese engineer Masatoshi Shima.[27]

The project that produced the 4004 originated in 1969, when Busicom, a Japanese calculator manufacturer, asked Intel to build a chipset for high-performance desktop calculators. Busicom's original design called for a programmable chip set consisting of seven different chips. Three of the chips were to make a special-purpose CPU with its program stored in ROM and its data stored in shift register read-write memory. Ted Hoff, the Intel engineer assigned to evaluate the project, believed the Busicom design could be simplified by using dynamic RAM storage for data, rather than shift register memory, and a more traditional general-purpose CPU architecture. Hoff came up with a four-chip architectural proposal: a ROM chip for storing the programs, a dynamic RAM chip for storing data, a simple I/O device and a 4-bit central processing unit (CPU). Although not a chip designer, he felt the CPU could be integrated into a single chip, but as he lacked the technical know-how the idea remained just a wish for the time being.

First microprocessor by Intel, the 4004.

While the architecture and specifications of the MCS-4 came from the interaction of Hoff with Stanley Mazor, a software engineer reporting to him, and with Busicom engineer Masatoshi Shima, during 1969, Mazor and Hoff moved on to other projects. In April 1970, Intel hired Italian engineer Federico Faggin as project leader, a move that ultimately made the single-chip CPU final design a reality (Shima meanwhile designed the Busicom calculator firmware and assisted Faggin during the first six months of the implementation). Faggin, who originally developed the silicon gate technology (SGT) in 1968 at Fairchild Semiconductor[28] and designed the world's first commercial integrated circuit using SGT, the Fairchild 3708, had the correct background to lead the project into what would become the first commercial general purpose microprocessor. Since SGT was his very own invention, Faggin also used it to create his new methodology for random logic design that made it possible to implement a single-chip CPU with the proper speed, power dissipation and cost. The manager of Intel's MOS Design Department was Leslie L. Vadász at the time of the MCS-4 development but Vadász's attention was completely focused on the mainstream business of semiconductor memories so he left the leadership and the management of the MCS-4 project to Faggin, who was ultimately responsible for leading the 4004 project to its realization. Production units of the 4004 were first delivered to Busicom in March 1971 and shipped to other customers in late 1971.

Along with Intel (who developed the 8008), Texas Instruments developed in 1970–1971 a one-chip CPU replacement for the Datapoint 2200 terminal, the TMX 1795 (later TMC 1795.) Like the 8008, it was rejected by customer Datapoint. According to Gary Boone, the TMX 1795 never reached production. Since it was built to the same specification, its instruction set was very similar to the Intel 8008.[29][30]

The TMS1802NC was announced September 17, 1971 and implemented a four-function calculator. The TMS1802NC, despite its designation, was not part of the TMS 1000 series; it was later redesignated as part of the TMS 0100 series, which was used in the TI Datamath calculator. Although marketed as a calculator-on-a-chip, the TMS1802NC was fully programmable, including on the chip a CPU with an 11-bit instruction word, 3520 bits (320 instructions) of ROM and 182 bits of RAM.[29][31][30][32]

Gilbert Hyatt was awarded a patent claiming an invention pre-dating both TI and Intel, describing a "microcontroller".[33] The patent was later invalidated, but not before substantial royalties were paid out.[34][35]

The Intel 4004 was followed in 1972 by the Intel 8008, the world's first 8-bit microprocessor. The 8008 was not, however, an extension of the 4004 design, but instead the culmination of a separate design project at Intel, arising from a contract with Computer Terminals Corporation, of San Antonio TX, for a chip for a terminal they were designing,[36] the Datapoint 2200—fundamental aspects of the design came not from Intel but from CTC. In 1968, CTC's Vic Poor and Harry Pyle developed the original design for the instruction set and operation of the processor. In 1969, CTC contracted two companies, Intel and Texas Instruments, to make a single-chip implementation, known as the CTC 1201.[37] In late 1970 or early 1971, TI dropped out being unable to make a reliable part. In 1970, with Intel yet to deliver the part, CTC opted to use their own implementation in the Datapoint 2200, using traditional TTL logic instead (thus the first machine to run "8008 code" was not in fact a microprocessor at all and was delivered a year earlier). Intel's version of the 1201 microprocessor arrived in late 1971, but was too late, slow, and required a number of additional support chips. CTC had no interest in using it. CTC had originally contracted Intel for the chip, and would have owed them US$50,000 (equivalent to $315,653 in 2019) for their design work.[37] To avoid paying for a chip they did not want (and could not use), CTC released Intel from their contract and allowed them free use of the design.[37] Intel marketed it as the 8008 in April, 1972, as the world's first 8-bit microprocessor. It was the basis for the famous "Mark-8" computer kit advertised in the magazine Radio-Electronics in 1974. This processor had an 8-bit data bus and a 14-bit address bus.[38]

The 8008 was the precursor to the successful Intel 8080 (1974), which offered improved performance over the 8008 and required fewer support chips. Federico Faggin conceived and designed it using high voltage N channel MOS. The Zilog Z80 (1976) was also a Faggin design, using low voltage N channel with depletion load and derivative Intel 8-bit processors: all designed with the methodology Faggin created for the 4004. Motorola released the competing 6800 in August 1974, and the similar MOS Technology 6502 was released in 1975 (both designed largely by the same people). The 6502 family rivaled the Z80 in popularity during the 1980s.

A low overall cost, little packaging, simple computer bus requirements, and sometimes the integration of extra circuitry (e.g. the Z80's built-in memory refresh circuitry) allowed the home computer "revolution" to accelerate sharply in the early 1980s. This delivered such inexpensive machines as the Sinclair ZX81, which sold for US$99 (equivalent to $278.41 in 2019). A variation of the 6502, the MOS Technology 6510 was used in the Commodore 64 and yet another variant, the 8502, powered the Commodore 128.

The Western Design Center, Inc (WDC) introduced the CMOS WDC 65C02 in 1982 and licensed the design to several firms. It was used as the CPU in the Apple IIe and IIc personal computers as well as in medical implantable grade pacemakers and defibrillators, automotive, industrial and consumer devices. WDC pioneered the licensing of microprocessor designs, later followed by ARM (32-bit) and other microprocessor intellectual property (IP) providers in the 1990s.

Motorola introduced the MC6809 in 1978. It was an ambitious and well thought-through 8-bit design that was source compatible with the 6800, and implemented using purely hard-wired logic (subsequent 16-bit microprocessors typically used microcode to some extent, as CISC design requirements were becoming too complex for pure hard-wired logic).

Another early 8-bit microprocessor was the Signetics 2650, which enjoyed a brief surge of interest due to its innovative and powerful instruction set architecture.

A seminal microprocessor in the world of spaceflight was RCA's RCA 1802 (aka CDP1802, RCA COSMAC) (introduced in 1976), which was used on board the Galileo probe to Jupiter (launched 1989, arrived 1995). RCA COSMAC was the first to implement CMOS technology. The CDP1802 was used because it could be run at very low power, and because a variant was available fabricated using a special production process, silicon on sapphire (SOS), which provided much better protection against cosmic radiation and electrostatic discharge than that of any other processor of the era. Thus, the SOS version of the 1802 was said to be the first radiation-hardened microprocessor.

The RCA 1802 had a static design, meaning that the clock frequency could be made arbitrarily low, or even stopped. This let the Galileo spacecraft use minimum electric power for long uneventful stretches of a voyage. Timers or sensors would awaken the processor in time for important tasks, such as navigation updates, attitude control, data acquisition, and radio communication. Current versions of the Western Design Center 65C02 and 65C816 have static cores, and thus retain data even when the clock is completely halted.

The Intersil 6100 family consisted of a 12-bit microprocessor (the 6100) and a range of peripheral support and memory ICs. The microprocessor recognised the DEC PDP-8 minicomputer instruction set. As such it was sometimes referred to as the CMOS-PDP8. Since it was also produced by Harris Corporation, it was also known as the Harris HM-6100. By virtue of its CMOS technology and associated benefits, the 6100 was being incorporated into some military designs until the early 1980s.

The first multi-chip 16-bit microprocessor was the National Semiconductor IMP-16, introduced in early 1973. An 8-bit version of the chipset was introduced in 1974 as the IMP-8.

Other early multi-chip 16-bit microprocessors include one that Digital Equipment Corporation (DEC) used in the LSI-11 OEM board set and the packaged PDP 11/03 minicomputer—and the Fairchild Semiconductor MicroFlame 9440, both introduced in 1975–76. In 1975, National introduced the first 16-bit single-chip microprocessor, the National Semiconductor PACE, which was later followed by an NMOS version, the INS8900.

Another early single-chip 16-bit microprocessor was TI's TMS 9900, which was also compatible with their TI-990 line of minicomputers. The 9900 was used in the TI 990/4 minicomputer, the Texas Instruments TI-99/4A home computer, and the TM990 line of OEM microcomputer boards. The chip was packaged in a large ceramic 64-pin DIP package, while most 8-bit microprocessors such as the Intel 8080 used the more common, smaller, and less expensive plastic 40-pin DIP. A follow-on chip, the TMS 9980, was designed to compete with the Intel 8080, had the full TI 990 16-bit instruction set, used a plastic 40-pin package, moved data 8 bits at a time, but could only address 16 KB. A third chip, the TMS 9995, was a new design. The family later expanded to include the 99105 and 99110.

The Western Design Center (WDC) introduced the CMOS 65816 16-bit upgrade of the WDC CMOS 65C02 in 1984. The 65816 16-bit microprocessor was the core of the Apple IIgs and later the Super Nintendo Entertainment System, making it one of the most popular 16-bit designs of all time.

Intel "upsized" their 8080 design into the 16-bit Intel 8086, the first member of the x86 family, which powers most modern PC type computers. Intel introduced the 8086 as a cost-effective way of porting software from the 8080 lines, and succeeded in winning much business on that premise. The 8088, a version of the 8086 that used an 8-bit external data bus, was the microprocessor in the first IBM PC. Intel then released the 80186 and 80188, the 80286 and, in 1985, the 32-bit 80386, cementing their PC market dominance with the processor family's backwards compatibility. The 80186 and 80188 were essentially versions of the 8086 and 8088, enhanced with some onboard peripherals and a few new instructions. Although Intel's 80186 and 80188 were not used in IBM PC type designs, second source versions from NEC, the V20 and V30 frequently were. The 8086 and successors had an innovative but limited method of memory segmentation, while the 80286 introduced a full-featured segmented memory management unit (MMU). The 80386 introduced a flat 32-bit memory model with paged memory management.

The 16-bit Intel x86 processors up to and including the 80386 do not include floating-point units (FPUs). Intel introduced the 8087, 80187, 80287 and 80387 math coprocessors to add hardware floating-point and transcendental function capabilities to the 8086 through 80386 CPUs. The 8087 works with the 8086/8088 and 80186/80188,[39] the 80187 works with the 80186 but not the 80188,[40] the 80287 works with the 80286 and the 80387 works with the 80386. The combination of an x86 CPU and an x87 coprocessor forms a single multi-chip microprocessor; the two chips are programmed as a unit using a single integrated instruction set.[41] The 8087 and 80187 coprocessors are connected in parallel with the data and address buses of their parent processor and directly execute instructions intended for them. The 80287 and 80387 coprocessors are interfaced to the CPU through I/O ports in the CPU's address space, this is transparent to the program, which does not need to know about or access these I/O ports directly; the program accesses the coprocessor and its registers through normal instruction opcodes.

Upper interconnect layers on an Intel 80486DX2 die

16-bit designs had only been on the market briefly when 32-bit implementations started to appear.

The most significant of the 32-bit designs is the Motorola MC68000, introduced in 1979. The 68k, as it was widely known, had 32-bit registers in its programming model but used 16-bit internal data paths, three 16-bit Arithmetic Logic Units, and a 16-bit external data bus (to reduce pin count), and externally supported only 24-bit addresses (internally it worked with full 32 bit addresses). In PC-based IBM-compatible mainframes the MC68000 internal microcode was modified to emulate the 32-bit System/370 IBM mainframe.[42] Motorola generally described it as a 16-bit processor. The combination of high performance, large (16 megabytes or 2²⁴ bytes) memory space and fairly low cost made it the most popular CPU design of its class. The Apple Lisa and Macintosh designs made use of the 68000, as did a host of other designs in the mid-1980s, including the Atari ST and Commodore Amiga.

The world's first single-chip fully 32-bit microprocessor, with 32-bit data paths, 32-bit buses, and 32-bit addresses, was the AT&T Bell Labs BELLMAC-32A, with first samples in 1980, and general production in 1982.[43][44] After the divestiture of AT&T in 1984, it was renamed the WE 32000 (WE for Western Electric), and had two follow-on generations, the WE 32100 and WE 32200. These microprocessors were used in the AT&T 3B5 and 3B15 minicomputers; in the 3B2, the world's first desktop super microcomputer; in the "Companion", the world's first 32-bit laptop computer; and in "Alexander", the world's first book-sized super microcomputer, featuring ROM-pack memory cartridges similar to today's gaming consoles. All these systems ran the UNIX System V operating system.

The first commercial, single chip, fully 32-bit microprocessor available on the market was the HP FOCUS.

Intel's first 32-bit microprocessor was the iAPX 432, which was introduced in 1981, but was not a commercial success. It had an advanced capability-based object-oriented architecture, but poor performance compared to contemporary architectures such as Intel's own 80286 (introduced 1982), which was almost four times as fast on typical benchmark tests. However, the results for the iAPX432 was partly due to a rushed and therefore suboptimal Ada compiler.

Motorola's success with the 68000 led to the MC68010, which added virtual memory support. The MC68020, introduced in 1984 added full 32-bit data and address buses. The 68020 became hugely popular in the Unix supermicrocomputer market, and many small companies (e.g., Altos, Charles River Data Systems, Cromemco) produced desktop-size systems. The MC68030 was introduced next, improving upon the previous design by integrating the MMU into the chip. The continued success led to the MC68040, which included an FPU for better math performance. The 68050 failed to achieve its performance goals and was not released, and the follow-up MC68060 was released into a market saturated by much faster RISC designs. The 68k family faded from use in the early 1990s.

Other large companies designed the 68020 and follow-ons into embedded equipment. At one point, there were more 68020s in embedded equipment than there were Intel Pentiums in PCs.[45] The ColdFire processor cores are derivatives of the 68020.

During this time (early to mid-1980s), National Semiconductor introduced a very similar 16-bit pinout, 32-bit internal microprocessor called the NS 16032 (later renamed 32016), the full 32-bit version named the NS 32032. Later, National Semiconductor produced the NS 32132, which allowed two CPUs to reside on the same memory bus with built in arbitration. The NS32016/32 outperformed the MC68000/10, but the NS32332—which arrived at approximately the same time as the MC68020—did not have enough performance. The third generation chip, the NS32532, was different. It had about double the performance of the MC68030, which was released around the same time. The appearance of RISC processors like the AM29000 and MC88000 (now both dead) influenced the architecture of the final core, the NS32764. Technically advanced—with a superscalar RISC core, 64-bit bus, and internally overclocked—it could still execute Series 32000 instructions through real-time translation.

When National Semiconductor decided to leave the Unix market, the chip was redesigned into the Swordfish Embedded processor with a set of on chip peripherals. The chip turned out to be too expensive for the laser printer market and was killed. The design team went to Intel and there designed the Pentium processor, which is very similar to the NS32764 core internally. The big success of the Series 32000 was in the laser printer market, where the NS32CG16 with microcoded BitBlt instructions had very good price/performance and was adopted by large companies like Canon. By the mid-1980s, Sequent introduced the first SMP server-class computer using the NS 32032. This was one of the design's few wins, and it disappeared in the late 1980s. The MIPS R2000 (1984) and R3000 (1989) were highly successful 32-bit RISC microprocessors. They were used in high-end workstations and servers by SGI, among others. Other designs included the Zilog Z80000, which arrived too late to market to stand a chance and disappeared quickly.

The ARM first appeared in 1985.[46] This is a RISC processor design, which has since come to dominate the 32-bit embedded systems processor space due in large part to its power efficiency, its licensing model, and its wide selection of system development tools. Semiconductor manufacturers generally license cores and integrate them into their own system on a chip products; only a few such vendors such as Apple are licensed to modify the ARM cores or create their own. Most cell phones include an ARM processor, as do a wide variety of other products. There are microcontroller-oriented ARM cores without virtual memory support, as well as symmetric multiprocessor (SMP) applications processors with virtual memory.

From 1993 to 2003, the 32-bit x86 architectures became increasingly dominant in desktop, laptop, and server markets, and these microprocessors became faster and more capable. Intel had licensed early versions of the architecture to other companies, but declined to license the Pentium, so AMD and Cyrix built later versions of the architecture based on their own designs. During this span, these processors increased in complexity (transistor count) and capability (instructions/second) by at least three orders of magnitude. Intel's Pentium line is probably the most famous and recognizable 32-bit processor model, at least with the public at broad.

While 64-bit microprocessor designs have been in use in several markets since the early 1990s (including the Nintendo 64 gaming console in 1996), the early 2000s saw the introduction of 64-bit microprocessors targeted at the PC market.

With AMD's introduction of a 64-bit architecture backwards-compatible with x86, x86-64 (also called AMD64), in September 2003, followed by Intel's near fully compatible 64-bit extensions (first called IA-32e or EM64T, later renamed Intel 64), the 64-bit desktop era began. Both versions can run 32-bit legacy applications without any performance penalty as well as new 64-bit software. With operating systems Windows XP x64, Windows Vista x64, Windows 7 x64, Linux, BSD, and macOS that run 64-bit natively, the software is also geared to fully utilize the capabilities of such processors. The move to 64 bits is more than just an increase in register size from the IA-32 as it also doubles the number of general-purpose registers.

The move to 64 bits by PowerPC had been intended since the architecture's design in the early 90s and was not a major cause of incompatibility. Existing integer registers are extended as are all related data pathways, but, as was the case with IA-32, both floating point and vector units had been operating at or above 64 bits for several years. Unlike what happened when IA-32 was extended to x86-64, no new general purpose registers were added in 64-bit PowerPC, so any performance gained when using the 64-bit mode for applications making no use of the larger address space is minimal.

In 2011, ARM introduced a new 64-bit ARM architecture.

In the mid-1980s to early 1990s, a crop of new high-performance reduced instruction set computer (RISC) microprocessors appeared, influenced by discrete RISC-like CPU designs such as the IBM 801 and others. RISC microprocessors were initially used in special-purpose machines and Unix workstations, but then gained wide acceptance in other roles.

The first commercial RISC microprocessor design was released in 1984, by MIPS Computer Systems, the 32-bit R2000 (the R1000 was not released). In 1986, HP released its first system with a PA-RISC CPU. In 1987, in the non-Unix Acorn computers' 32-bit, then cache-less, ARM2-based Acorn Archimedes became the first commercial success using the ARM architecture, then known as Acorn RISC Machine (ARM); first silicon ARM1 in 1985. The R3000 made the design truly practical, and the R4000 introduced the world's first commercially available 64-bit RISC microprocessor. Competing projects would result in the IBM POWER and Sun SPARC architectures. Soon every major vendor was releasing a RISC design, including the AT&T CRISP, AMD 29000, Intel i860 and Intel i960, Motorola 88000, DEC Alpha.

In the late 1990s, only two 64-bit RISC architectures were still produced in volume for non-embedded applications: SPARC and Power ISA, but as ARM has become increasingly powerful, in the early 2010s, it became the third RISC architecture in the general computing segment.

A different approach to improving a computer's performance is to add extra processors, as in symmetric multiprocessing designs, which have been popular in servers and workstations since the early 1990s. Keeping up with Moore's law is becoming increasingly challenging as chip-making technologies approach their physical limits. In response, microprocessor manufacturers look for other ways to improve performance so they can maintain the momentum of constant upgrades.

A multi-core processor is a single chip that contains more than one microprocessor core. Each core can simultaneously execute processor instructions in parallel. This effectively multiplies the processor's potential performance by the number of cores, if the software is designed to take advantage of more than one processor core. Some components, such as bus interface and cache, may be shared between cores. Because the cores are physically close to each other, they can communicate with each other much faster than separate (off-chip) processors in a multiprocessor system, which improves overall system performance.

In 2001, IBM introduced the first commercial multi-core processor, the monolithic two-core POWER4. Personal computers did not receive multi-core processors until the 2005 introduction, of the two-core Intel Pentium D. The Pentium D, however, was not a monolithic multi-core processor. It was constructed from two dies, each containing a core, packaged on a multi-chip module. The first monolithic multi-core processor in the personal computer market was the AMD Athlon X2, which was introduced a few weeks after the Pentium D. As of 2012, dual- and quad-core processors are widely used in home PCs and laptops, while quad-, six-, eight-, ten-, twelve-, and sixteen-core processors are common in the professional and enterprise markets with workstations and servers.

Sun Microsystems has released the Niagara and Niagara 2 chips, both of which feature an eight-core design. The Niagara 2 supports more threads and operates at 1.6 GHz.

High-end Intel Xeon processors that are on the LGA 775, LGA 1366, and LGA 2011 sockets and high-end AMD Opteron processors that are on the C32 and G34 sockets are DP (dual processor) capable, as well as the older Intel Core 2 Extreme QX9775 also used in an older Mac Pro by Apple and the Intel Skulltrail motherboard. AMD's G34 motherboards can support up to four CPUs and Intel's LGA 1567 motherboards can support up to eight CPUs.

Modern desktop computers support systems with multiple CPUs, but few applications outside of the professional market can make good use of more than four cores. Both Intel and AMD currently offer fast quad, hex and octa-core desktop CPUs, making multi-CPU systems obsolete for many purposes. The desktop market has been in a transition towards quad-core CPUs since Intel's Core 2 Quad was released and are now common, although dual-core CPUs are still more prevalent. Older or mobile computers are less likely to have more than two cores than newer desktops. Not all software is optimised for multi-core CPUs, making fewer, more powerful cores preferable.

AMD offers CPUs with more cores for a given amount of money than similarly priced Intel CPUs—but the AMD cores are somewhat slower, so the two trade blows in different applications depending on how well-threaded the programs running are. For example, Intel's cheapest Sandy Bridge quad-core CPUs often cost almost twice as much as AMD's cheapest Athlon II, Phenom II, and FX quad-core CPUs but Intel has dual-core CPUs in the same price ranges as AMD's cheaper quad-core CPUs. In an application that uses one or two threads, the Intel dual-core CPUs outperform AMD's similarly priced quad-core CPUs—and if a program supports three or four threads the cheap AMD quad-core CPUs outperform the similarly priced Intel dual-core CPUs.

Historically, AMD and Intel have switched places as the company with the fastest CPU several times. In 2012, Intel led on the desktop side of the computer CPU market, with their Sandy Bridge and Ivy Bridge series, while at the same time, AMD's Opterons had superior performance for their price point. AMD were therefore more competitive in low- to mid-end servers and workstations that more effectively used fewer cores and threads.

Taken to the extreme, this trend also includes manycore designs, with hundreds of cores, with qualitatively different architectures.