CISC and RISC

Simplified instruction sets and Complex Instruction Sets

We can think about how to transfer the data of a cache to B. You only need to enable a in the read status and then enable B in the write status, you can do this in two steps. However, if the CPU is required to search for a word in a certain segment in the memory, the microinstruction encoding must be arranged more. Therefore, the complexity of microservices can be divided into Reduced Instruction Set Computer and Complex Instruction Set Computer CISC (Complex Instruction Set Computer ).

 

Complex Instruction Set computers(CISC)

In the long term, the improvement of computer performance is often achieved by increasing the complexity of hardware. with the integrated circuit technology. in particular, the rapid development of the very large scale integrated circuits technology, in order to facilitate software programming and improve the speed of program operation, hardware engineers are constantly adding instructions that can implement complex functions and a variety of flexible addressing methods. even some commands support complex operations after advanced language statements are classified. as the hardware becomes more and more complex, the cost also increases accordingly. to implement complex operations, the microprocessor provides programmers with functions similar to various registers and machine commands. the microprogram stored in the read-only memory (ROM) is also used to implement its strong functions. Proud to perform a series of basic command operations after analyzing each command to complete the required functions, this design type is called the Complex Instruction Set Computer-CISC structure. generally, CISC computers contain at least 300 commands.

Some of the above may even exceed 500.

 

Simplified Instruction Set Computer(RISC)

Computers using complex command systems have a strong ability to process advanced languages. this is helpful for improving computer performance. when computer design goes along this path. some people do not follow the stream. they looked back at the path they had taken and began to doubt this traditional approach: IBM did not have jhomasi in Yorktown, New York. wason Research Center organized forces to study the rationality of command systems in 1975. at that time, it was felt that the increasingly complex command system was not easy to implement. it may also reduce system performance. in 1979, a group of scientists headed by Professor Paterson started the study at the American University of California, Berkeley. the results show that CISC has many disadvantages. first. in this computer. the usage of various commands varies greatly: the 80% commands used in the calculation process of a typical program. accounts for only 20% of the Instruction System of one processor. in fact, the most frequently used commands are the simplest commands, such as getting, storing, and adding. in this way, the long-term commitment to the design of complex command systems is actually to design a processor that is rare to use in practice. at the same time. complex command systems will inevitably bring about structural complexity. this not only increases the design time and cost, but also easily leads to design errors.. although the current level of the very high level of the technology, it is difficult to make all the CISC hardware on a single chip, which also hinders the development of a single chip computer. in CISC, many complex commands require extremely complex operations. Most of these commands are directly revised in a certain advanced language, which leads to poor universality. because of the second-level microcode execution method, it also reduces the running speed of simple command systems that are frequently called. because. these disadvantages of CISC. paterson and others proposed the idea that the command system should only contain a small number of commands that are frequently used. and provide some necessary commands to support the operating system and high-level languages. A computer developed in accordance with this principle is called a simplified instruction set computer (AES) structure. short.

 

CISCAndProteusDifference

We often talk about topics related to "PC" and "Macintosh", but how many people know that the PC series with intel X86 as the core is based on the CISC architecture, while Apple's Macintosh is based on the structure of the RISC system. What is the difference between the CISC and the Proteus?

From the hardware point of view, CISC processes the instruction set of unequal length. It must separate the instruction set of unequal length. Therefore, a large amount of processing work is required when executing a single instruction. In contrast, assume that the CPU runs a short instruction set with a high speed and stable performance when executing commands. Therefore, in the aspect of parallel processing, the number of commands is much better than that of CISC. The number of commands that can be executed by a single command can be divided into several processes or threads, which can be executed by multiple processors at the same time. Due to the execution of a simplified instruction set, the manufacturing process is simple and cost-effective.

From the software perspective, CISC runs DOS and Windows operating systems that we know well. It also has a large number of applications. Because more than 65% of software vendors around the world are responsible for the PC and Its compatible machine services based on the CISC architecture, the well-known Microsoft is one of them. But in this regard, he seems a little weak. Although DOS and Windows can also be run on the server Load balancer, a translation process is required, so the operation speed is much slower.

Simply put, the design of complex and simplified instruction sets is completely different. The two processors also have different ways of thinking at work. Complex Instruction sets are more suitable for processing high-density computing tasks, while streamlined instruction sets are more suitable for processors to do simple and repetitive tasks. For example, what should we do if we want to execute the job of getting up and going to work in the morning? At this time, we only need to issue the command to go to work, and then we will automatically execute a series of complex actions, such as getting up, dressing, cleaning, going out, boarding, and other commands; to streamline the instruction set, we need to issue a simple command to us separately. Let's execute the command that he issued step by step and finally reach the goal of going to work.

This is the reason why the two are not performing well. This idea leads to a huge difference between the CISC and the RISC processors. The former focuses more on high performance but also requires high power consumption, the latter focuses on small-size and low-power fields. When performing high-density computing tasks, CISC is more advantageous, and when performing simple repetitive operations, the best advantage is.