Software Tip 2b

About the Disk Cache

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  • Especially in Windows versions 95 and 98 it is important to understand the of the relationship between:

  • Size of and control of Disk cache
  • The free memory
  • The size of the swap file

    What is disk cache?

    The cache is a portion of RAM, reserved for cache (buffer) for the hard disk. The disk cache is necessary, since it speeds up the hard disk a lot. However, it should not be bigger than 8 or 16 MB.

    The problem is that the disk cache really gobbles up RAM. In Windows 98 it can easily eat up 20-25% of your RAM. An that is a total waste of RAM.

    In Windows 98 you can limit the size of your cache. This is done by editing the file System.Ini, which is found in C:\Windows. Double click on it and scroll down until you reach the text [vcache].

    Then type in the two lines you see below and save the file. Do it soon. This is important!

    [Non Windows App]

    [vcache]
    MinFileCache=8096
    MaxFileCache=8096

    [display]

    The change takes effect when you restart Windows. I am convinced that 8 MB disk cache is sufficient - at least when you use the FAT32 file system.

    If you use Windows 95 with the old FAT16 file system, you should probably maintain just 1 or 2 MB of disk cache.

    In Fat 32 the vcache holds a permanent copy of the whole FAT table, which occupies full 2 MB under the FAT32 file system. With this size FAT the Vcache has to be 4 MB big, if there shall be room for other things besides the FAT.


    Read about file systems and about the cache copy of FAT in same module.


    The System Monitor

    You can watch your use of memory with the excellent tool resource meter . You find it by going to: Start -> Programs -> Accessories -> System Tools -> System Monitor. You can add elements in the edit menu. That will allow you to see available memory and the swap file, as illustrated below (you may print this page, although the figure is in Danish):

    You should check available memory and the size of the swap file over a period of time. Do this daily for a while and see how big the swap file gets.

    It is also a good idea to check the disk cache, so that it does not occupy more than 16 MB (or less). If the disk cache only occupies 8 or 16 MB, you can easily calculate your actual RAM usage by keeping track of available memory and the size of the swap file.


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    Copyright (c) 1996-2001 by Michael B. Karbo.