Shulou(Shulou.com)06/01 Report--

In order to tighten the contradiction between the high speed of CPU and the low speed of Imax O equipment, the offline output / input technique is introduced. The trick is to use a special core controller to transfer data from the low-speed Icano device to a high-speed disk; or vice versa. SPOOLing means simultaneous online operation of internal equipment, also known as spooling output / input operation, which is a technique used in piecemeal operations to transform unique equipment into shared equipment.

The piecemeal composition of SPOOLing is shown in figure 5-11.

Output well and input well

Two storage areas carved out on disk. The output well imitates the disk when the output is offline and is used to receive the data input by the Igamot O equipment. The input well imitates the disk of offline input and is used to hold the input data of the user program.

Figure 5-11 composition of SPOOLing bits and pieces

Output buffer and input buffer

Two buffers opened up in memory. The output buffer is used to temporarily store the data sent by the output equipment and transmit it to the output well in the future. The input buffer is used to temporarily store the data sent from the input well and then transfer it to the input equipment later.

Output process and input process

The output process imitates the core controller when the output is offline, sending the data requested by the user from the output machine through the output buffer to the output well. When CPU needs to output data, it reads the data directly from the output well into memory. The input process imitates the core controller of offline input, sending the data requested by the user from the memory to the input first, and then sending the data in the input well to the input equipment through the input buffer when the input equipment is free.

Shared printers are an example of the use of SPOOLing techniques, which have been widely used in multi-user piecemeal and local collection. When the user process asks for print input, SPOOLing piecemeal agrees to print input for it, but does not really immediately assign the printer to the user process, but only does two things for it:

A free disk block area is requested in the input well by the input process, and the data to be printed is sent into it.

The input process then requests a blank user request print table for the user process, fills in the user's print request, and then hangs the form on the request print queue.

The minor features of SPOOLing are: the improvement of the speed of Istroke O; the transformation of unique equipment into shared equipment; and the completion of virtual equipment functions.

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