Fifth chapter-Computer composition

The components of a computer can be divided into three main categories: the central processing Unit (CPU), the primary memory, the input/output subsystem.

Central processing Unit: Arithmetic logic unit (ALU), control Unit, register group.

Arithmetic logic units: logical (with, or, not, XOR) data, shifts (logical shifts and arithmetic shifts) and arithmetic operations.

Register: A high-speed, independent storage unit used to hold temporary data. (Data register, instruction register, program counter)

Control unit: Controls the operation of each subsystem.

main Memory: He is a collection of storage units, each of which has a unique identity, called an address. The data is passed in and out in memory in the form of a bit group called a word. The word can be 8-bit, 16-bit, 32-bit, if the word is 8 bits, commonly called 1 bytes.

Address space: Each word in the memory needs to have a corresponding marker. (b= bytes)

Memory type: RAM and ROM

Memory structure: main memory (slowest, cheaper)-Cache memory-register (fastest, expensive)

Buffer memory: Often placed between the CPU and main memory. Contains a copy of a portion of main memory at any time.

When the CPU wants to access a word in main memory, it will proceed as follows: (8-2 rules)

1.CPU check the buffer memory first.

2. If the word to be accessed exists, the CPU copies it, and if it does not, the CPU copies it from main memory. The data block will overwrite the contents of the buffer memory.

3.CPU access the buffer memory and copy the word.

Input/Output subsystems: Non-storage devices and storage devices.

Non-storage devices: Keyboard, monitor, printer

Storage device: Disk (need to know), tape, optical storage device,,,,

Interconnection of subsystems

Connection of CPU and memory

　　The CPU and memory are usually connected by three groups of lines called buses, respectively, the data bus, address bus, control bus.

Data bus: 1 bits of data are transmitted per root. The number of lines depends on the size of the computer's word. For example, if the word in the computer is 32 bits (4 bytes), then 32 lines of data bus are required so that 32-bit words can be delivered at the same time.

Address bus: Allows access to a word in memory, the number of lines address bus depends on the size of the storage space. If the storage capacity is 2n characters, then address bus need to transfer n-bit address data at a time. Therefore, he needs n bus.

Control bus: Responsible for transmitting information between the CPU and the memory. For example, a code must be sent from the CPU to memory to specify whether a read or write operation is performed, and the number of lines that control the bus depends on the total number of control commands required by the computer. If there are 2n control commands, then the total control I Sheenah will need to be n root, because n bits can define 2n different operations.

Connections to I/O devices

Neither the input/output devices can be directly connected to the bus that connects the CPU and memory. Because the input/output device is inherently different from the CPU and memory, the input/output devices are electromechanical, magnetic or optical devices, while the CPU and memory are electronic devices. The input/output device operates much more slowly than the CPU and memory. Therefore there must be an intermediary to handle this discrepancy, and the input/output device is connected to the bus via a device called an input/output controller or interface. Each input/output device has a specific controller.

　　

Chapter fifth-Computer composition