Types of Processors Cisc Processors




Types of Processors Cisc Processors

One of the earlier goals of CPU designers was to provide more and more instructions in the instruction set of a CPU to ensure that the CPU supports more functions directly. This makes it easier to translate high-level language programs to machine language and ensures that the machine language programs run more effectively. Of course, every additional instruction in the instruction set of a CPU requires additional hardware circuitry to handle that instruction, adding more complexity to the CPU's hardware circuitry. Another goal of CPU designers was to optimize the usage of expensive memory.

To achieve this, designers tried to pack more instructions in memory by introducing the concept of variable-length instructions such as half-word, one-and-half-word, etc. For example, an operand in an immediate instruction needs fewer bits, and hence, a CPU designer can design it as a half-word instruction. Additionally, designers originally designed CPUs to support a variety of addressing modes (discussed later in this chapter during the discussion of memory). CPUs with large instruction set, variable-length instructions, and a variety the discussion of memory). CPUs with large instructions set, variable-length instructions, and modes are called CPUs based on CISC (Complex Instruction Set Computer) architecture. Since CISC processors possess so many processing features, they make the job of machine language programmers easier. However, they are complex and expensive to produce. Most modern personal computers use CISC processors.

CISC was developed to make compiler development easier and simpler. The full form of CISC is Complex Instruction Set Computer. They are chips that are easy to program that makes efficient use of memory. CISC eliminates the need for generating machine instructions to the processor. For example, instead of having to make a compiler, write lengthy machine instructions to calculate a square-root distance, a CISC processor offers a built-in ability to do this. Many of the early computing machines were programmed in assembly language. Computer memory was slow and expensive.