Free Essay

Risc Nad Cisc Processors

In: Computers and Technology

Submitted By shipra
Words 837
Pages 4
Topic: - Study of various RISC and CISC processors

ABSTRACT:- This term paper presents two instructions set architectures, particularly the CISC and the RISC, which have been developed as computer architects aimed for a fast, cost-effective design. Included in this paper are the arguments made for each architecture, and of some performance comparisons on RISC and CISC processors. These data are collected from various papers published concerning the RISC versus CISC discussion.

INTRODUCTION: - RISC, or Reduced Instruction Set Computer is a type of microprocessor architecture that utilizes a small, highly-optimized set of instructions, rather than a more specialized set of instructions often found in other types of architectures. Though it may seem less effective for a computational task to be executed with many simple instructions rather than a few complex instructions, the simple instructions take fairly the same amount of time to be performed, making them ideal for pipelining. CISC is an acronym for Complex Instruction Set Computer and are chips that are easy to program and which make efficient use of memory. Since the earliest machines were programmed in assembly language and memory was slow and expensive, the CISC philosophy made sense, and was commonly implemented in such large computers as the PDP-11 and the DEC system 10 and 20 machines

The first RISC projects came from IBM, Stanford, and UC-Berkeley in the late 70s and early 80s. The IBM 801, Stanford MIPS, and Berkeley RISC 1 and 2 were all designed with a similar philosophy which has become known as RISC. Certain design features have been characteristic of most RISC processors: * One cycle execution time: RISC processors have a CPI (clock per instruction) of one cycle. This is due to the optimization of each instruction on the CPU and a technique called. * pipelining: a technique that allows for simultaneous execution of parts, or stages, of instructions to more efficiently process instructions; * large number of registers: the RISC design philosophy generally incorporates a larger number of registers to prevent in large amounts of interactions with memory
During the late 1980s and early 1990s, RISC processors began to replace CISC in the embedded applications which account for almost all microprocessor volume, and by the end of the decade market consolidation was well under way.

Types of RISC processors:- Alpha, ARC, ARM, MIPS, SPARC.
Some types are described below: 1. Alpha, originally known as Alpha AXP, is a 64-bit reduced instruction set computer (RISC) instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC), designed to replace the 32-bit VAX complex instruction set computer (CISC) ISA and its implementations. 2. ARM is a 32-bit reduced instruction set computer (RISC) instruction set architecture (ISA) developed by ARM Holdings. It was named the Advanced RISC Machine, and before that, the Acorn RISC Machine. The ARM architecture is the most widely used 32-bit instruction set architecture in numbers produced. Originally conceived by Acorn Computers for use in its personal computers, the first ARM-based products were the Acorn Archimedes range introduced in 1987.

Characteristics of RISC processors:- * Uniform instruction format, using a single word with the opcode in the same bit positions in every instruction, demanding less decoding; * Identical general purpose registers, allowing any register to be used in any context, simplifying compiler design (although normally there are separate floating point registers); * Simple addressing modes, with complex addressing performed via sequences of arithmetic and/or load-store operations; * Few data types in hardware, some CISCs have byte string instructions, or support complex numbers; this is so far unlikely to be found on a RISC.

Types of CISC processors:- System/360 through z/Architecture, PDP-11, VAX, Motorola 68k, and x86.
Some types are described below:
1. PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years. The PDP-11 had several uniquely innovative features, and was easier to program than its predecessors with its use of general registers. Its successor in the mid-range minicomputer niche was the 32-bit VAX-11.
2. The Motorola 680x0/m68000/68000 is a family of 32-bit CISC microprocessors. During the 1980s and early 1990s, they were popular in computers and workstations and were the primary competitors of Intel's x86 microprocessors. They were most well known as the processors powering the early Apple Macintosh, the Commodore Amiga, the Sinclair QL, the Atari ST, SEGA Mega drive/Genesis and several others. Although no modern desktop computers are based on the 68000, derivative processors are still widely used in embedded applications.

Characteristics of RISC processors:- * large number of addressing modes * variable length instruction encoding * support for misaligned accesses * many instructions that access memory directly

REFERENCES:- 1. 2. 3. 4.

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