CISC VS. RISC

RISC vs. CISC computers

RISC vs. CISC computers

CISC Computers

CISC is the acronym for Complex Instruction Set Computer and is named so because a lot of instructions are needed to set up a program. CISC are the oldest form of chips available, and they require a huge number of complex instructions to work. It is very difficult to design a CPU with CISC chips because they require a number of instructions (Creasey, 1962, pp. 10). CISC became popular because initially programming was done through assembly language, and the memory was expensive as well as slow. CISC has made life easy for programmers because there are huge numbers of instructions and with these few instructions they can easily convert the high level language to assemble language. Despite its drawbacks, CISC is still being used in today's world. (See Appendix for diagram)History of CISC

The first CISC computer was launched by Intel. CISC made the programming easy in the early days because these chips allowed a number of instructions to be built on a single chip. Memory was expensive; therefore, CISC allowed copious instructions to be stored in one single chip and because the programming was directly fed in the processor (Emerson, 1999, pp. 15). With the passage, of time CISC became more and more complex because more instructions were added to the design of the processor. The major drawback 'complexity' of CISC has not affected its use in the market. Even today most of the desktop computer market is captured by CISC processors (Tabak, 1996).

Advantages of CISC

No reinvention needed

Whenever a new design of CISC was introduced in the market, there was no need to reinvent the codes or the design cycle. The new design could build on its predecessor's instruction set. This made CISC an ever growing language which is the main reason it is being used till now.

Few Instructions

The CISC required few instructions to implement a new program. This led to lower memory use for the purpose of program storage, and it also helped to do things quicker, less time was required by the processor to fetch instructions from the memory.

Simple for compilers

As complex as the CISC instructions are, they did not leave much to do for the compilers because fiddly instructions resembled assembly language. CISC instructions when merged with assembly language made up high-level languages, and there was little left for the compiler to do.Disadvantages of CISC

Increased Complexity

One of the major disadvantages of CISC is the complexity of instructions. All the instructions are fed in one memory chip, and because new sets of instructions are fed in the same chip, it makes the whole process very complex. This is the reason why CISC became bulky.

Not used frequently

In order to justify their use, most of the specialized CISC instructions were not used frequently. Each instruction had to be justified because each instruction requires microcode storage, which is built, in at some cost.

Time consuming

CISC is time consuming mainly due to its complexity. Each CISC instruction is translated into hundreds of microcode lines; therefore, it runs slower than most of the other translations. All translations take time, but CISC translations takes longer than usual because of its instructions.

Complex hardware design

The design of CISC hardware is very complex. Every instruction is translated into microcode for execution ...