1. the role of peripherals in the computer 2. peripherals in the computer in what way 3. host and peripheral what kinds of transmission mode

1. External devices referred to as "peripherals", refers to the hardware devices connected to the computer outside the host. Data and information on the role of transmission, transfer and storage, is an important part of the computer system. Due to the wide variety of peripheral devices, some devices have multiple functions, so far, it is difficult to make an accurate classification of peripheral devices. According to the different functions, can be roughly divided into input devices, display devices, printing devices, external memory and network equipment five categories.

2. Peripherals generally work in a program interrupt mode, please refer to /ch05/5-1-3.htm

3. There are the following three ways to transfer data between the CPU and peripherals: program mode, interrupt mode, and DMA mode.

Program mode: the program mode can be divided into two ways: unconditional transmission mode and conditional transmission mode. The unconditional transfer method is generally used when the CPU peripheral transfers data less frequently. In the CPU is used to transfer data for a long time and the number of peripherals is not much when the conditional transfer method.

Interrupt mode: In real-time systems and systems with multiple peripherals, interrupt mode is used in order to improve the efficiency of the CPU and make the system have real-time performance. If the data transfer efficiency of an I/O device is high, the data transfer between the CPU and such a peripheral is still unsatisfactory even if the non-data transfer time is compressed as much as possible in the program query method and the interrupt method.

DMA mode: This is because in both modes, there is another reason for the speed impact, which is that they both transfer bytes or words. In order to solve this problem and realize the transfer by data block, it is necessary to change the transfer method, which is the direct memory transfer method, i.e. DMA method.