mian yang teachers college

Principles of Computer Organization (Final Paper)

Memory of microcomputer

Author * * *

Class 7, Grade 07, Unit Counting College (07084207**)

Lecturer * * *

The working time of the thesis is May 2009.

abstract

With the rapid popularization and development of microcomputers, people's functional requirements for computers are no longer limited to simple calculation and data processing, but are developing towards multimedia computers and large entertainment computers that integrate images, sounds and words. In this development process, memory has gradually become the focus of attention. Here, we will introduce the related knowledge of memory in further detail.

key word

Classification performance index of microcomputer memory

Memory is the most important storage device in a computer system, which can store a large number of computer programs and data, not only receive information (data and programs) in the computer, but also save information, and also read the saved information according to the command.

Memory can be divided into main memory and auxiliary memory by function, and internal memory and external memory by storage location.

The performance index of memory is mainly determined by capacity, access speed, reliability and cost performance.

Classification of the Memories

Memory can be divided into main memory (referred to as main memory) and auxiliary memory (referred to as auxiliary memory) according to functions. The main memory is a memory with relatively fast access speed and small capacity, while the auxiliary memory is a memory with relatively slow access speed and large capacity.

Main memory, also called memory, is directly connected to the CPU, and is the main working memory in the computer. Currently running programs and data are stored in the memory.

Auxiliary memory is also called external memory (external memory for short). When the computer executes programs and processes data, the information in the external memory is sent to the memory in the form of blocks or groups before it can be used, that is, the computer uses the information in the external memory by constantly exchanging data with the memory.

The number of bytes contained in memory is called storage capacity. Storage capacity is usually expressed in KB, MB or GB, where B is a byte, 1KB= 1024B, 1MB= 1024KB, 1GB= 1024MB. For example, 640KB is 640× 1024=655360 bytes.

(1) internal memory

Modern internal memories are mostly semiconductor memories, using large-scale integrated circuits or very large-scale integrated circuit devices. Internal memory can be divided into random access memory (RAM) and read-only memory (ROM) according to its different working modes.

Random access memory. Random Access Memory (RAM) allows random storage or retrieval of information in any storage unit with any specified address, and the access time to any address is the same. Because information is written into memory through electrical signals, the information in RAM will disappear when power is cut off. Programs and data used in computer work are stored in memory. If the program or data is modified, it should be stored in external memory, otherwise the information will be lost after shutdown. Generally speaking, the memory size refers to the size of RAM, usually in KB or MB.

Read only memory. Read-only memory is a memory that can only read information but can't write information at will. The contents in ROM are written by the manufacturer in a special way, or can be written by a special writer. When the computer is powered off, the information in the ROM will not be lost. When the computer is powered on again, the information in it remains unchanged and can still be read. ROM is suitable for storing important information such as boot program started by computer, detection program after startup, basic input and output program of system, clock control program, system configuration of computer, disk parameters, etc.

(2) External memory

The commonly used external memory of PC is floppy disk (referred to as floppy disk) and hard disk (referred to as hard disk). At present, the use of optical discs is becoming more and more popular. The following are three commonly used external memories:

Floppy disk: At present, floppy disks commonly used in computers are divided into 5.25-inch disks (referred to as 5-inch disks) and 3.5-inch disks (referred to as 3-inch disks).

The main differences between them are: the size of 3.5-inch disk is smaller than that of 5.25-inch disk, and it is made of hard plastic, which is not easy to bend and damage; The edge of the 3.5-inch disk has a movable metal slider to protect the disk. The read-write slot is located under the metal slider and usually has a cover: 3.5-inch disk has no index hole; The write protection device of 3.5-inch disk is a square hole in the corner of the disk and a slider. When the slider closes the hole, the disk can be read and written, and when the hole is opened, the disk is write-protected.

The format of recording information on floppy disk is to divide the disk into many concentric circles, called tracks. Tracks are numbered from outside to inside, and information is recorded on the tracks. In addition, several lines radiating from concentric circles divide each track into several sectors and number them in sequence. In this way, the location of the information stored on the floppy disk can be found by the track number and sector number. A complete floppy disk storage system consists of floppy disk, floppy disk drive and floppy disk drive adapter card.

Floppy disks can only store data. If you want to read or write data, you must also have a floppy drive. The floppy disk drive is located in the main chassis and consists of two parts: the magnetic head and the driving device. The magnetic head is used to locate the track, and the function of the driving device is to make the disk rotate at high speed, so as to read and write the disk. The floppy drive adapter card is a special interface board connecting the floppy drive and the motherboard, and is connected with the floppy drive through a 34-core flat cable.

Hard disk: In terms of data storage principle and storage format, hard disk and floppy disk are exactly the same. But the magnetic material of hard disk is coated on the hard disk substrate made of metal, ceramics or glass, while the substrate of floppy disk is plastic. Compared with floppy disks, hard disks mainly have large storage space, and now the capacity of hard disks is above 160GB. Hard disks are mostly composed of multiple disks. At this time, in addition to each disk being divided into several tracks and sectors, the tracks corresponding to the surfaces of multiple disks will form multiple concentric cylinders in space.

Usually, the hard disk is installed in the main chassis of the computer, but now there are many kinds of mobile hard disks. This kind of mobile hard disk is connected to the computer through USB interface, which is convenient for users to carry large-capacity data.

CD-ROM: With the popularization of multimedia technology, CD-ROM is quickly welcomed by people because of its large capacity, long life and low cost. Compared with magnetic disk, optical disk is read and written by laser beam through optical head in optical disk drive. At present, there are three kinds of optical discs used in computer systems: CD-ROM, CD-R and CD-RW.

Memory performance index

1, memory capacity Memory capacity refers to the total amount of binary information that memory can hold, that is, the total number of bits of stored information. Assuming that the number of bits of the address line and data line of the microcomputer are p and q respectively, the total number of address units of the memory chip is 2p, and the bit capacity of the memory chip is 2p× q ... For example, if the memory chip is 6 1 1 address lines and 8 data lines, the bit capacity of the chip is: bit capacity. Therefore, memory capacity is sometimes expressed in bytes. For example, the capacity of the above-mentioned 6 1 16 chip is 2KB, which is marked as 2K ×8, where: 1kB = 1024b (bytes) = 1024× 8 = 8 192. At present, the capacity of memory chips is getting bigger and bigger, and the price is getting lower and lower, which is mainly due to the development of large-scale integrated circuits.

2. The speed of accessing the speed memory directly affects the speed of the computer. Access speed can be measured by two time parameters: access time and storage period. Access time refers to the time it takes for the CPU to send a valid memory address to start a memory read-write operation until the read-write operation is completed. The shorter the time, the faster the access speed. At present, the access time of cache memory is less than 5ns. The storage cycle is the minimum time interval required to start two independent memory operations continuously, which is generally slightly longer than the access time.

3. Reliability

The reliability of memory is measured by MTBF (mean time between failure) mean time between failure. The longer the MTBF, the higher the reliability. Error correction coding technology is often used to extend MTBF to improve reliability.

4. Performance-price ratio

This is a comprehensive indicator, and the performance mainly includes the above three indicators-storage capacity, storage speed and reliability. Different uses of memory have different requirements. For example, some memories need storage capacity, so storage capacity is the main one; Some memories, such as cache, are mainly based on storage speed.

General purpose memory now

A, the characteristics of semiconductor memory classification

1, characteristics of semiconductor memory

(1) is fast, and the access time can reach ns level;

(2) High integration, which not only occupies a small space for storage units, but also can be decoded.

Circuits, buffer registers, read-write circuits and so on are all made on the same chip. At present, it has reached 1024Mb (equivalent to 128 MB) on a single chip.

(3) Non-destructive reading, that is, after reading the information, the information in the storage unit still exists, especially the static RAM, which does not need to be regenerated after reading.

(4) Volatility of information (for RAM), that is, information is lost after power failure.

5] Volatility of information (for DRAM), that is, the stored information will be lost after a certain period of time, so it should be regenerated (refreshed) regularly.

Low power consumption, especially CMOS memory.

Once the volume is small, the price is falling.

2, the classification of semiconductor memory

Mainly divided into two categories, read-write memory RAM and read-only memory ROM.

RAM is divided into static RAM(SRAM) and dynamic RAM(DRAM). At present, the main memory in the computer is DRAM, which has high integration and low power consumption. The disadvantage is that it needs regeneration. SRAM is nonvolatile and does not need regeneration, but its integration is lower than DRAM. Most cache memories in computers use SRAM. Now there are some new RAM, such as combined RAM(IRAM), which integrates the refresh circuit with d RAM. Nonvolatile RAM(NVRAM) is actually composed of SRAM and EEPROM. In general, just like general SRAM, the information in SRAM is saved in EEPROM at the moment of power failure, so that the information is not lost. The characteristic of ROM is that users can only read the information in it, but can't modify and write the information. In recent years, a new type of memory called flash memory has appeared, which is an electrically erasable nonvolatile read-only memory.

Second, the composition of semiconductor memory

It generally consists of memory banks, address selection circuits, input and output circuits and control circuits.

1, memory stick

A bank is a circuit entity that stores 1 and 0 information. It consists of many memory cells, and each memory cell generally consists of several bits (8 bits). Each bit needs a memory cell, and each memory cell has a number called an address. The address of the memory is represented by a set of binary numbers, and the relationship between the number n of address lines and the number n of memory cells is 2n = n.

2. Address selection circuit

The address selection circuit includes an address decoder and an address code register. The address decoder is used to decode the address. Assume that there are n address lines at the input end and n address lines at the output end, corresponding to 2n different address codes as the selection lines of the address unit. The selection lines of these outputs are also called word lines. There are two ways to decode an address:

(1) single decoding mode

All its address codes are decoded by only one circuit, and the decoded word selection line directly selects the corresponding storage unit. This method requires a large number of selection lines and is only suitable for small-capacity memories.

(2) Double decoding mode (or matrix decoding)

It divides the address code into two parts, X and Y, which are decoded by two decoding circuits. X-direction decoding is called row decoding, and its output line is called row selection line, which selects all memory cells in a row in the memory matrix. Y direction decoding is also called column decoding, and its output line is called column selection line, which selects all cells in a column. Only one-bit memory cells selected by the X-direction and Y-direction selection lines can be read and written. As can be seen from the figure, the memory bank with 1024 basic cells is arranged in a 32×32 matrix, and its X-direction and Y-direction decoders each have 32 decoding output lines, ***64. If a single decoding method is used, 1024 decoding output lines are needed. Therefore, the double decoding method requires fewer selection lines and simplifies the structure of the memory, so it is suitable for large-capacity memory.

3. Read-write control circuit

The read-write control circuit includes read-write amplifier, data register (tri-state bidirectional buffer) and so on. It is a channel for data information input and output. The external control signals of the memory include a read signal RD, a write signal WR and a chip selection signal CS.

refer to

1, Principles of Computer Organization, 2nd Edition, edited by Tang Shuofei, Higher Education Press, 2008+0.

2. Principles and Applications of Microcomputer, edited by Xiao Jinli, Electronic Industry Press, 2003- 1.

3. The experimental instruction and problem set of Computer Organization Principles (Wang Cheng, Zhou Jiqun, Cai) were published by Tsinghua University Publishing House.

4. Learning Guidance and Training of Computer Organization Principles (edited by Kuang, Jiang Hanyang) was published by China Water Resources and Hydropower Publishing House.