【正文】 in the implementation of a task, only the relevant procedures and raw data transferred from the disk on a smaller memory capacity, CPU and memory through highspeed data processing, and then the final result will be rewritten into the disk through the memory. This configuration affordable, integrated access speed is faster. To address highspeed CPU and a relatively slow speed of main memory of the contradictions, the cache may also be used. It is fast, the prices higher static semiconductor memory, or even to do together with the microprocessor to store the current most frequently used instructions and data. When the CPU reads instructions from memory and data, will also visit the cache and main memory. If the content required in the cache, you can immediately access。 If not, then read from the main memory. The contents of the cache is based on the actual situation in a timely replacement. In this way, by adding a small amount of the cost of high speed can be obtained. 2, using disk as the OutofCore is not only cheap, can do a great storage capacity, but also in power when it does not lose the information stored can be longterm preservation of, and copying, very convenient to carry. The relationship between the memory Memory Categories Overview 1. Storage medium by Category (1) semiconductor memory posed of semiconductor devices with memory as the semiconductor memory。 features: integrated highcapacity, small size, fast access, low power consumption, cheap, simple to maintain. Two main categories: bipolar memory: TTL and ECL type. Memory metaloxide semiconductor (MOS memory): static and dynamic MOS memory MOS memory. (2) the surface magnetic memory using magnetic materials made of the surface magnetic memory called memory, or magnetic memory. It includes disk memory, tape memory. Characteristics: size, degree of automation, low production, slow access, but the storage capacity is much greater than the semiconductor memory and not lost. (3) laser memory information stored in the form of scratch disk, the disk with a laser beam through the different reflectivity of the disk to read out information. CDROM can be divided into readonly type optical disk (CDROM), a writeonly type optical disk (WORM) and magnetooptical disk (MOD) in three. 2. Classification according to access (1) random access memory (RAM): If the memory contents of any memory cell can be random access, and memory cell access time and physical location has nothing to do, then this memory is called Random Access Memory (RAM). RAM is mainly used to store a variety of input / output procedures, data, puting intermediate results and storing the information exchange with the outside world and to do with the stack. Mainly act as a random access memory cache and main memory. (2) serial access memory (SAS): If the memory can only be accessed by some kind of order, that is, memory cell access time and physical location, such as the serial access memory storage. Memory can be divided into sequential serial access memory (SAM) and directaccess memory (DAM). Sequential access memory is fully serial access memory, such as tape, and information to the order of the storage medium from the beginning of the beginning of write (or read)。 Direct is part of the serial access memory access memory, such as disk storage, it between the order of between access and random access. (3) readonly memory (ROM): ROM is a read not only its contents into the memory, that is a prewrite memory. Usually used to store fixed information. Often used as a microprogram control, such as memory. So far, the readonly memory can be rewritten. Common mask ROM (MROM), Erasable Programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM). ROM than RAM circuit of simple, highly integrated, low cost, and is a nonvolatile memory, the puter often a number of management and control procedures and mature in the user program on the ROM. 3. Information can be stored according to classification Nonpermanent memory storage: after poweroff information on the disappearance of the memory, such as semiconductor read / write memory RAM. Permanent memory storage: After the power of memory can store information, such as magnetic materials made of semiconductor memory, as well as ROM. In accordance with the puter system in the role of sub – Memory in the puter system in accordance with the role can be divided into the main memory, auxiliary memory, cache memory, such as control. To address the requirements of large capacity memory, fast, low cost of the contradictions between the current monly used multilevel memory architecture, that is, the use of cache memory, main memory and external memory. Use of the name referred to the characteristics of Cache cache of highspeed access instructions and data access speed, but the storage capacity of small Main memory storage of the puter main memory during operation of a large number of procedures and data access speed and storage capacity is not OutofCore storage systems outside the process memory and large data files and databases Storage capacity, low cost digital 4. Memory How it works Introduced here only dynamic memory (DRAM) working principle. Dynamic memory each has only one input data line, while only 8 address pins. In order to form a 64K address, must be in the system address bus and chip address pin address between the formation of a specially designed circuit. The system address bus signals can be time to add the address of the pin 8, the use of the line chip latches, latch out and decoding circuit chip of the selected memory cell, latch signals also depend on address the external circuit. When readfrom the DRAM chip when, CPU will first address line added to the A0A7 on the latches and then sent RAS signal, the falling edge of the signal to address the existence of the chip internal lock. Then add the chips out the address A0A7 on, send the CAS signal latch, but als