Cisc and Risc microprocessors.
A microprocessor chip consists of several subunits. The microprocessor executes the instructions serially. The instructions are executed at very high speed. The microprocessor is more powerful if it can execute more instructions per second.
The traditional approach is to construct the microprocessors consisting of many instructions and build seperate internal circuits to execute or carry out these instructions. A microprocessor can execute these instructions because of the physical circuits performing these jobs. These physical circuits are the combinations of logical gates present in the microprocessor chip. For example, the complex addition circuit inside the microprocessor executes the addition instructions, whereas, the multiplication circuits execute the multiplication instructions. Similarly, the logical instructions such as comparison or branching are performed by the logical circuits present inside the microprocessor chip. For executing certain specialized instructions the microprocessor chip consists of specialized circuits inside the chip. As a consequence, Whenever the microprocessor chip manufacturer wants to include more and more specialized instructions into the microprocessor chip, for improving its versatility, more and more circuits have to be added. This inevitably results in increasing the size of the microprocessor chip and also in the heat produced.The microprocessor thus looses out on performance. Such an approach to building the microprocessor chip is adopted by Intel corporation and is known as Complex Instruction Set Computers. (CISC.) Microprocessors such as the Intel MMX and the AMD K6 use CISC architecture and are used in general purpose Destop and mobile computers.
A Computer Scientist by the name of John Cocke demonstrated that the microprocessor could really be built using only a few important instructions, rather than using many specialized instructions. He demonstrated that the about 20% of the instructions do 80% of the work. This principle is known as the 80-20 rule. Cooke’s research pointed out that complex and complicated instructions are really combinations of few important instructions. This resulted in the development of a new trend in microprocessor design known as the Reduced Instruction Set Computers. (RISC). Just as Intel specialised in the manufacture of CISC microprocessors, Motorola specialised in the design and development of RISC microprocessor. RISC architecture requires less amount of circuitry to build a microprocessor chip, thus improving the performance of the CPU.RISC cpus such as the DEC Alpha or MIPS orion 4600 decices appear in number of high end LAN servers and workstations.
Hence, the CISC and the RISC have developed into two competing technologies in the CPU design world. The former one is more versatile as there are specialized circuits for each instructions. However, it gives rise to bulky microprocessors and dissipation of lot of heat, resulting in diminished performance characteristics. The RICS microprocessor on the other hand is not very versatile, but is less bulky and dissipates much less heat, resulting in more stable and error free operation. It is also easier to build the RISC microprocessor than the CISC microprocessor. Designers are off-course on a search for developing microprocessors which can combine the versatality of the CISC architecture with the performance of the RISC architechture.
MeanWhile Intel, AMD amd Cyrix Corporations has from time to time announced entirely new developments in microprocessor chip designs, Forward – looking developments use long instruction words. These architechtures use advanced techniques such as pipelining, instruction predictions, branch eliminations and speculative loading and achieves prallel operation of processors inside the microprocessor chip.These new developments have been incorporated in the Intel, AMD K6 and the Cyrix microprocessor chips.
The traditional approach is to construct the microprocessors consisting of many instructions and build seperate internal circuits to execute or carry out these instructions. A microprocessor can execute these instructions because of the physical circuits performing these jobs. These physical circuits are the combinations of logical gates present in the microprocessor chip. For example, the complex addition circuit inside the microprocessor executes the addition instructions, whereas, the multiplication circuits execute the multiplication instructions. Similarly, the logical instructions such as comparison or branching are performed by the logical circuits present inside the microprocessor chip. For executing certain specialized instructions the microprocessor chip consists of specialized circuits inside the chip. As a consequence, Whenever the microprocessor chip manufacturer wants to include more and more specialized instructions into the microprocessor chip, for improving its versatility, more and more circuits have to be added. This inevitably results in increasing the size of the microprocessor chip and also in the heat produced.The microprocessor thus looses out on performance. Such an approach to building the microprocessor chip is adopted by Intel corporation and is known as Complex Instruction Set Computers. (CISC.) Microprocessors such as the Intel MMX and the AMD K6 use CISC architecture and are used in general purpose Destop and mobile computers.
A Computer Scientist by the name of John Cocke demonstrated that the microprocessor could really be built using only a few important instructions, rather than using many specialized instructions. He demonstrated that the about 20% of the instructions do 80% of the work. This principle is known as the 80-20 rule. Cooke’s research pointed out that complex and complicated instructions are really combinations of few important instructions. This resulted in the development of a new trend in microprocessor design known as the Reduced Instruction Set Computers. (RISC). Just as Intel specialised in the manufacture of CISC microprocessors, Motorola specialised in the design and development of RISC microprocessor. RISC architecture requires less amount of circuitry to build a microprocessor chip, thus improving the performance of the CPU.RISC cpus such as the DEC Alpha or MIPS orion 4600 decices appear in number of high end LAN servers and workstations.
Hence, the CISC and the RISC have developed into two competing technologies in the CPU design world. The former one is more versatile as there are specialized circuits for each instructions. However, it gives rise to bulky microprocessors and dissipation of lot of heat, resulting in diminished performance characteristics. The RICS microprocessor on the other hand is not very versatile, but is less bulky and dissipates much less heat, resulting in more stable and error free operation. It is also easier to build the RISC microprocessor than the CISC microprocessor. Designers are off-course on a search for developing microprocessors which can combine the versatality of the CISC architecture with the performance of the RISC architechture.
MeanWhile Intel, AMD amd Cyrix Corporations has from time to time announced entirely new developments in microprocessor chip designs, Forward – looking developments use long instruction words. These architechtures use advanced techniques such as pipelining, instruction predictions, branch eliminations and speculative loading and achieves prallel operation of processors inside the microprocessor chip.These new developments have been incorporated in the Intel, AMD K6 and the Cyrix microprocessor chips.
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