Composition of I/O System

Speaking of Basic Input/Output Systems, we are not unfamiliar at all. From the beginning of our contact with the computer to the present, the mouse, keyboard, and monitor may be what we have been using, but these devices alone cannot form an I/O System, which can only be regarded as a part of the I/O System-peripherals (I/O hardware). In addition to peripheral devices, I/O hardware includes I/O interfaces. Only hardware without house arrest, this system can only be a pile of scrap iron, so the I/O software and I/O hardware together make up the computer's I/O System.

Here is the content list:

l I/O software

l I/O command

l Channel command

I/O software

The so-called I/O software is simply used to control the I/O hardware, which is divided into two parts: I/O instructions and channel instructions. The main task of the I/O System is to process the data input by the user and convert it into data that can be recognized by humans and then output it. For example, I am trying to type on the keyboard now, and the characters entered through the keyboard are converted into Chinese characters through the input method, and finally displayed on the screen. Although it is not accurate, it is roughly the same process.

I/O command

The I/O instruction is a part of the CPU instruction, and the basic format is as follows: [opcode|command code|device code]. The operation code is a control instruction, such as memory access, arithmetic and logic operations, etc. The command code is to execute specific instructions, such as addition, subtraction, multiplication, and division in arithmetic and logic operations, and the device code is the number of the peripheral device in the multifunctional and finely modular. Through the I/O command, the basic control of the I/O device can be realized.

Channel command

Speaking of channel commands, we need to first understand the development history of the I/O System. In the early I/O system, because there were few devices, I/O devices were directly connected to the CPU. Once there were too many devices, it would cause a serious burden on the CPU, so there was an interface connection method. The interface is connected between the I/O bus and the I/O device and acts as a bridge. The interface can not only buffer data but also process interrupts. Finally, with the correct logic, devices can occupy the CPU in time-sharing, greatly improving the speed. The DMA that appeared later also played a role in improving efficiency. DMA can directly exchange data between the main memory and I/O devices, further liberating the CPU. Although the DMA method is good, on the mainframe, there are too many I/O devices and the interaction is very frequent. The CPU not only needs to manage many DMAs but also the control is very complicated, which directly affects the efficiency of the CPU. kind of structure. A channel can be understood as a special processor whose function is similar to that of a CPU. Its function is only to process data passing through the channel and reduce the burden on the CPU. All in all, the channel command is the channel's command, which is used to execute I/O commands, such as reading and writing disks, controlling the working status of I/O devices, and so on.

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