Lab 16.2: Configuring Caching

Cache is a term that describes a type of memory space used to store frequently used data. The first Microsoft caching program was SMARTDRV. This was replaced by VCACHE in Windows 98. Windows NT has its own programs to handle caching. When the computer is operating efficiently, the majority of information needed by the user and the processor is located in cache. When data is written or read from the main memory, a copy is placed into cache with the main memory address. Cache then monitors subsequent reads to see if the data is already in cache. If the data is in cache, then a cache hit is recorded and the main memory read is aborted. If the data is not in cache, then it is fetched from the main memory. If cache is not configured properly, then the system wastes a lot of CPU cycles retrieving needed data.

Upon completion of this lab, you will be able to configure caching for Windows 98, Windows 2000, and Windows XP.

Set Up

For this lab, you will need a computer running Windows 98 and a computer running Windows 2000 or Windows XP.

Exercises

You must take care when configuring cache in any Windows environment. The configuration requires that you alter either the system.ini file for Windows 98 or the Registry for Windows 2000/XP. A mistake in these settings can cause the system to become unbootable. The right setting, however, can improve system performance by allowing the system to use part of your RAM as cache.

Note

In Windows 98, do not use SMARTDRV. Windows 98 uses VCACHE, a routine that is an improvement of SMARTDRV; if you use SMARTDRV, the two will conflict with each other and decrease performance.

Configuring VCACHE

1. Right-click on My Computer and select Properties. Record the amount of RAM in your system. Then close the System Properties window.

2. Right-click on My Computer and select Explore from the menu.

3. Navigate to the Windows directory.

4. In the Windows directory, locate the system.ini file. Right-click on it and select Open from the menu. Doing so opens the system.ini file in Notepad.

5. Locate the section labeled [vcache].

6. Locate the entry MinFileCache=. Change the value based on Table 16.1.

7. Locate the entry MaxFileCache=. Change the value based on Table 16.1.

   Note

   You may have to type the entries into the system.ini file. Type them exactly as shown in steps 6 and 7.

   Table 16.1: System.ini VCACHE Values

   RAM	MinFileCache	MaxFileCache
   16MB	1024	4096
   16MB–32MB	2048	8192
   32MB–64MB	8192	16384
   > 64MB–128MB	16384	32768
   > 128MB	32768	65536

8. Save the file and close it. Reboot the system for the changes to take effect.

Setting Cache Setting in the Registry

1. In Windows 2000 or Windows XP, from the Run command, type regedt32.

2. When the Registry Editor opens, navigate to the Memory Management key:

   HKey_Local_Machine\System\CurrentControlSet\Control\Session
   Manager\Memory Management

3. Locate the value LargeSystemCache. Double-click to open it for editing.

4. Change the Data field value to 1 if it is not already set. This value turns on the Large System Cache function that allows the operating system to use all unused RAM as cache.

5. Reboot the system for the changes to take effect.