CISC, RISC, VLIW, and EPIC Architectures
The first commercial microprocessor was the Intel 4004, introduced by Intel Corporation more than 30 years ago, in 1971. This 4-bit processor was followed by 8-bit, 16-bit, 32-bit, and 64-bit processors from Intel Corporation and other manufacturers. The most successful family of processors started with the 16-bit Intel 8086, which set the basis for the Intel x86 architecture (also referred to as IA-32).
CISC and RISC
The x86 processors belong to the CISC (Complex Instruction Set Computing) category, mainly because their instructions may be quite complex or have variable length. They use a relatively small number of registers, and are capable of accessing memory locations directly. Complex instructions are sequenced in microcode in modern CISC processors.
A different line, derived from CISC, is represented by the RISC (Reduced Instruction Set Computing) processors introduced in the 1980s, which are characterized mostly by how they differ from CISC processors. The instructions are of fixed length, and of a regular format. Operations are performed on registers only, of which a larger number are available than on CISC processors. The only memory operations are load and store. The hardware in RISC processors is simpler in principle than in CISC ones, because a RISC architecture relies more on the compiler for sequencing complex operations.
Advances in both CISC and RISC processors were possible on one hand through technological progress in the manufacturing area, and on the other through new processor architecture and microarchitecture features.
Technological advances in manufacturing, driven...
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