Brief introduction of spooling technology of virtual machine

Virtual machine is one of the four main features of the OS, if you can use a multi-channel program technology to virtual a physical CPU for more than one logical CPU, allowing multiple users to share a host, then, through the spooling technology can be a physical I/O device virtual for more than one logical I/O set, Also allows multiple users to share a single physical I/O.

1, what's the matter spooling

To ease the contradiction between CPU speed and the low speed of I/O devices, the introduction of offline input, offline output technology, which is dedicated to the use of specialized peripheral controllers, spooling technology is a low-speed input and host exchange of a technology, usually also known as "spool really online", His core idea is to get offline in a way that works online. Low-speed devices are connected by channels and peripherals in the host memory buffer memory with high-speed devices, which are usually secondary storage. To store information entered from a low-speed device, or to store information (from memory) that will be output to a low-speed device, open a fixed area, called an "output well" (for output), or "input well" (for input), respectively, in the secondary storage. In short, it is in memory to form a buffer, in the advanced equipment to form output wells and input wells, transmission, from the low-speed equipment into the buffer, and then to the high-speed equipment input wells, and then from the high-speed equipment output wells, to the buffer, and then spread to low-speed equipment.

2, the composition of the spooling system

A, input well and output well

b, input buffer and output buffer

c, input processes and output processes

3, the characteristics of the spooling system

(1) Increased I/O speed. The operation of I/O from the low-speed I/O device into an input or output well, as with offline operation, improves I/O speed and eases the contradiction between CPU and low-speed I/O device speed mismatch.

(2) The device is not assigned to any process. In an input or output well, the process is assigned to a storage area and an I/O request table is established. (3) Realize the virtual equipment function. Multiple processes use a single device at the same time, and for each process, it is considered exclusive, but the device is a logical device