Disk cache is a static area in RAM set aside to help the Macintosh work more quickly and efficiently.
When a program asks for data from the disk (such as a part of a document), many times the next piece of data the program will need (such as the next part of the document) can be anticipated. Therefore, instead of transferring from disk to memory only the amount of data you are immediately working with, the system puts a larger amount (the size-of-disk-cache) of data into memory. This way, instead of spending the time to search for data on the disk again, the next piece of information will already be available. Disk cache works better on non-fragmented disks.
It may seem that the size-of-disk-cache should be configured to be quite large so that the need to search on the disk is greatly reduced. But this is not so because the memory allocated to disk cache cannot be used for opening more applications or documents. Thus, giving disk cache a huge amount of memory only makes that unavailable for use as RAM; it will not result in an increase in performance.
If the total memory of your system software appears to be very large under "About this Macintosh..." you should consider decreasing the memory allotted to disk cache. Open the Memory control panel and click the down arrow in the Disk Cache box.
This article was published in the Information Alley on 19 April 1996.