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Disk Caching Software Accelerates PC Computin |
The information in this document applies to:
WordPerfect® 5.1 for DOS
Problem
Solutions: A disk cache accelerates PC computing time by using speedy RAM for tasks usually performed by sluggish hard disks. Explanation of Disk Caching: 1. When you boot up, disk caching software allocates itself a buffer of expanded or extended memory (anywhere from 512K to several megabytes). Some caches take a specific amount of memory for the buffer; others take all the memory that's available and later release it to programs that need it for processing. 2. When you load a program, the CPU goes to the hard disk for data. The cache intercepts the request and then finds the needed files--either program or data files. Next, the cache reads the files into its buffer for the CPU to access directly. The CPU treats the disk cache as if it's a hard drive. 3. During clock cycles when the CPU would otherwise be idle, the cache reads more data into the buffer from sectors near the files that have already been read. This second-guessing anticipates that data in nearby sectors may soon be needed--a feature that works best with defragmented disks. 4. When the program needs more data, the CPU looks first in the cache. But if the data is not there, the cache retrieves it from the disk and stores it to feed to the CPU. As the cache fills up, it releases the data that's been in the buffer the longest. 5. Some caches intercept commands to the system's memory management software. If a program requires more memory (e.g., to index a complex database), the cache tells the memory manager to free up caching memory so that the program can carry the task. 6. When the program saves data, some caches intercept the data and defer writing it to disk until the CPU is idle. If the data file is still in the cache, only the sectors that have changed are written to disk. Some caches also hold pending writes and perform them in an order that minimizes the movements of the disk and drive head. |
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