Published in 1971, the first microprocessor was a 4-bit microprocessor with 4m5 KB memory which had a series of 45 instructions. Microprocessor speed has doubled every two years in the past 5 decades, as predicted by Intel co-founder Gordon Moore. Actual microprocessors are able to access 64 GB of memory. We belong to these classifications, based on the size of data microprocessors may process.
A further important consideration is the size of instruction set while categorizing microprocessors. Microprocessors initially had very small sets of instructions because complex hardware was both expensive and difficult to build.
As technology developed to overcome these problems, increasingly complex instructions were added to increase microprocessor functionality. But soon it was realized that having large instruction sets was counterproductive as many instructions that sat idle on precious memory space were seldom used. So the popularity gained from the old school of thought which supported smaller instruction sets.
RISC stands for Reduced Instruction Set Computers. It has a small set of highly optimized instructions. Simpler instructions are often used to execute complicated instructions, growing the scale of instruction collection. The RISC architecture theory combines these highlights –
RISC processors include Intel P6, Pentium4, AMD K6 and K7, etc.
CISC stands for Complex Instruction Set Computers. It stands for hundreds of instructions. CISC-supporting computers can do a wide variety of tasks, making them ideal for personal computers. These are certain features of CISC architecture-
CISC processors are for example Intel 386 & 486, Pentium, Pentium II and III, Motorola 68000, etc.
EPIC calls for Explicitly Parallel Instruction Computing. It's a computer architecture which is a hybrid between RISC and CISC, trying to offer the best of both. The main features are −
Such Awesome processors include Intel IA-64, Itanium, etc.