Checking memory amount
To check on how much memory a Mac has, choose About This Macintosh ...... (or About the Finder...... under System 6 ) from the apple menu when you are on the desktop (or Finder) and look at the total memory figure.
The Disk Cache
A disk cache (called RAM cache is System 6) is a portion of memory set aside to hold information your Mac would otherwise have to read from disk. When cache is on, everything you do that requires disk access is stored there (or as much of it is as there is room foe in the cache), so the next time you do the same thing the information is retrieved from RAM much more quickly than it could be from the disk. Using a disk cache speeds up all sorts of operations on your Mac, including opening and quitting programs, loading portions of programs, loading portions of programs like spelling checkers and switching between active programs.
Normally Cache Size = 25% of Total RAM on a computer.
To lock an individual file or application program just select the icon, choose get info from the
File menu in the Finder and check locked in the dialog box that appears.
System 7 is real memory hog, and even if you have 8MB of memory (which incidentally, is only scarcely enough for the newest System 7.5.1), you may run short once in a while. Here are several ways to free up a little extra memory:
- Go to the Memory control panel and reduce the size of disk cache to its lowest setting.
- Close unnecessary programs and desk accessories.
- Don't assign more memory than necessary to the programs you have running (see setting an applications current memory below)
- Launch frequently used programs first to avoid memory fragmentation ( see memory fragmentation below)
- Use special utilities inside programs, like word processor's spelling checker, or EndNote, sparingly. They take up RAM that would otherwise be available for documents.
- Remove unnecessary fonts and sounds from your system folder.
- Cut down on the number of system extensions in the extensions folder and the number of control panels in the Control Panels folder. Each one alone usually doesn't take up a lot of memory, but together they can add up. If you have to have a lot use an Extensions Manager utility.
- Be sure you have allocated enough memory to the Finder when you are using large storage devices.
Memory fragmentation
Works the same as Disk Fragmentation. Largest unused block.
RAM Disks
A RAM Disk is a portion of the memory that's set aside to act as a temporary disk. You use a utility program (e.g. Connectix's Virtual 3.0 and Apple ApplDisk) to create the RAM disk, which then appears as an icon on your desktop. You can use a RAM disk as you would any other disk, but when you shut off your computer, everything in the RAM disk disappears (remember RAM is volatile).
So what good is it? Well, what's stored in the RAM disk can be retrieved a lot faster than what's stored on the disk. Put an application there and you will notice virtually all its operations speed up. Put your System and Finder there and all the things they do will speed up.
So why not do it? RAM is expensive: $40/MB
Virtual Memory
Virtual Memory is sort of opposite of a RAM disk - its a technique that lets the computer use part of the hard disk as if it were RAM. Portions of large files or programs get swapped from RAM to the virtual memory section of the disk and back again as needed. Virtual memory is useful for large graphics, long animations, complex sounds, lots of scanning and keep a lot of files open at the same time.
Why not do it? A lot slower than real RAM.
Why do it? CHEAP: (almost 2MB/dollar)
The notes are based on The Macintosh Bible, 4th Edition, Arthur Naiman et. al., Peachpit Press, 1987-92.
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