RISC and CISC
CISC and RISC
There are different types of CPUs in existence. For example, there are the Intel 80x86 processors upon which today’s home computers are based (also known as IBM compatibles and variations thereof). With these types of processors, you can load up operating systems such as Windows and Linux. Then there are the 680x0 processors upon which the Apple Macs are based. Each type of CPU has its own set of machine code instructions that it can work with. All of the instructions together for any particular CPU are known as the CPU’s 'instruction set'. One type of CPU will not be able to use the same instruction set as a completely different CPU.
The above types of processors are sometimes referred to as CISC, or Complex Instruction Set Computers. These processors have complex instructions which can be carried out in just one single ‘fetch decode execute’ cycle. They have many different addressing modes and a wide range of instructions that can be used
There are also CPUs that are known as RISC (pronounced ‘risk’), or Reduced Instruction Set Computers. RISC processors such as ultra-SPARC and ALPHA use a much smaller, simpler set of instructions than CISC processors and so to carry out any particular programming task may take many ‘fetch decode execute’ cycles. RISC processors, however, are much more efficient at processing huge blocks of data than CISC.