AMD Athlon 64 X2 3600 Dual core processor
Main article: Multi-core (computing)
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 the physical limits of the technology.
In response, the microprocessor manufacturers look for other ways to improve performance, in order to hold on to the momentum of constant upgrades in the market.
A multi-core processor is simply a single chip containing more than one microprocessor core, effectively multiplying the potential performance with the number of cores (as long as the operating system and software is designed to take advantage of more than one processor). Some components, such as bus interface and second level cache, may be shared between cores. Because the cores are physically very close they interface at much faster clock speeds compared to discrete multiprocessor systems, improving overall system performance.
In 2005, the first mass-market dual-core processors were announced and as of 2007 dual-core processors are widely used in servers, workstations and PCs while quad-core processors are now available for high-end applications in both the home and professional environments.
Sun Microsystems has released the Niagara and Niagara 2 chips, both of which feature an eight-core design. The
Apple produces the Mac Pro which also utilizes an 8-core Intel Xeon processor that can operate up to 3.2 GHz.
RISC
In the mid-1980s to early-1990s, a crop of new high-performance RISC (reduced instruction set computer) microprocessors appeared, which were initially used in special purpose machines and Unix workstations, but then gained wide acceptance in other roles.
The first commercial design was released by MIPS Technologies, the 32-bit R2000 (the R1000 was not released). The R3000 made the design truly practical, and the R4000 introduced the world's first 64-bit design. Competing projects would result in the IBM POWER and Sun SPARC systems, respectively. 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 and the HP-PA.
Market forces have "weeded out" many of these designs, with almost no desktop or laptop RISC processors and with the SPARC being used in Sun designs only. MIPS is primarily used in embedded systems, notably in Cisco routers. The rest of the original crop of designs have disappeared. Other companies have attacked niches in the market, notably ARM, originally intended for home computer use but since focussed on the embedded processor market. Today RISC designs based on the MIPS, ARM or PowerPC core power the vast majority of computing devices.
As of 2007, two 64-bit RISC architectures are still produced in volume: SPARC and Power Architecture. The RISC-like Itanium is produced in smaller quantities. The vast majority of 64-bit microprocessors are now x86-64 CISC designs from AMD and Intel.
Special-purpose designs
Though the term "microprocessor" has traditionally referred to a single- or multi-chip CPU or system-on-a-chip (SoC), several types of specialized processing devices have followed from the technology. The most common examples are microcontrollers, digital signal processors (DSP) and graphics processing units (GPU). Many examples of these are either not programmable, or have limited programming facilities. For example, in general GPUs through the 1990s were mostly non-programmable and have only recently gained limited facilities like programmable vertex shaders. There is no universal consensus on what defines a "microprocessor", but it is usually safe to assume that the term refers to a general-purpose CPU of some sort and not a special-purpose processor unless specifically noted.
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