A cache (pronounced "cash") is a temporary holding area in the computer's memory where the computer stores information that is used repeatedly. The computer can access the information much more quickly from the cache than if the information was stored in the usual place (which might be on a disk or in a part of the computer's memory that takes longer to access). The term cache can also be used as a verb-"to cache" means to place information in the cache.
The basic idea behind a disk cache is that working with information stored in memory (RAM) is much faster than working with information stored on disk. A disk cache is a software utility that works by reserving a section of memory where it keeps a copy of information that was previously read from your disks. The next time your computer needs that same information, the data can be accessed directly from the cache, bypassing the slower disk. But if the cpu (central processing unit, the chip that runs the computer) needs data that is not in the disk cache, then it has to go to the disk and get it, in which case there is no advantage to having part of your memory set aside for the disk cache.
Since related data is often physically adjacent on a disk, the cache may also make a copy of information near the data that was previously used, in expectation that the extra data will eventually be needed. However, since there's limited room in the cache, only a fraction of the information on your disk is in the cache at anyone time. But the caching utility manages things so that the information your software most often uses stays in the cache.
Some disk caching utilities also cache files you want to save, as well as other information your computer is trying to store on the disk. Because the cache sends this data to the disk in small drips and drabs instead of all at once, you don't have to wait until the saving process is finished before going back to work. Although you'll see ads saying that a disk cache "speeds up your hard disk," the disk doesn't actually run any faster-it just doesn't get used as often.
On a Macintosh, you can choose how much memory to set aside as a disk cache through the Memory Control Panel. In System 6 you can turn off the cache altogether; in System 7 you can reduce it to 16K. Keep in mind that any amount you set as disk cache takes away from your main memory. If you have 2MBor less in your computer, turn the cache off or down to16K,since with less than a 256Kcache you won't even notice a difference, and you really can't spare any if all you have is 2MB.With 4MBor more of memory, try setting your cache between 256Kand 1,024Kand see if you notice a performance improvement. If you don't notice an improvement, turn it down as low as possible because there is no sense setting aside that memory space if it's not doing you any good.
With IBM-compatible computers, you have to run your disk caching utility as a device driver (via your CONFIG.SYS file) or as a memory resident program (usually by including it in your AUTOEXEC.BAT file). Microsoft includes a decent caching utility called SMART Drive with Windows and with MS-DOS versions 5.0 and greater. If you're willing to pay extra, you can get still faster caching utilities from other manufacturers; the most popular cache is Super pC-Kwik.