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MAPC_OFF.INF - DISABLE MAPPING OF CACHED PAGES
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Windows 98 supports the mapping of cached pages to increase the
amount of memory available to running applications. The Windows 98
memory manager architecture divides memory into 2 parts:
- Protected-mode disk cache (VCACHE)
- Memory allocated to run programs and hold data (VMM)
Reading from memory is much faster than reading from the hard disk.
VCACHE improves performance by reducing the number of times the hard
disk is accessed. A process in memory will demand a particular
section of code; if that section of code is in VCACHE, it can be
accessed and used much more quickly than if that section of code
needs to be read from a file on disk. For example, if you were to
launch an application, close it, and then shortly thereafter launch
it a second time, the application's launch time would now be
noticeably reduced. This is a result of copying much of the
application from VCACHE instead of the hard disk.
Memory allocated to the disk cache is not available to executing
processes. Reducing the amount of memory available to running
applications negatively impacts performance by increasing the amount
of data swapped from memory to the hard disk. Once again, reading
from memory is much faster than reading from the swap file on the
hard disk.
In Windows 95, there are two instances of some code in physical
memory; one instance stored in the disk cache to reduce the time
required to load the application should it be invoked again, and
another instance in VMM for the running application. Eliminating the
instance of the data in the cache would increase the amount of memory
available to VMM, but would negatively impact application reload times.
Windows 98 supports the mapping of cached pages to increase the
amount of memory available to running applications. Memory mapped
I/O from the cache eliminates needless duplication of data while
the application is running. Application code is loaded into VCACHE,
and then executes out of the cache rather than having to be copied
to another part of memory before it executes. When the application is
closed, the memory manager labels the space that application was
using as not currently being used to maintain the benefits of
caching--if the application is not restarted, that space is given to
other tasks. If the application is restarted, the application still
exists in the cache, maintaining improved application reload times.
Windows 98 maps cached pages by default. This performance enhancement
can be disabled by creating a MapCache entry in the registry key
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\VMM
If the MapCache entry does not exist, Windows 98 will map cached
pages. Creating the MapCache entry will disable the mapping of
cached pages.
To create the registry entry for MapCache:
1. Select MAPC_OFF.INF in the \Tools\MTSutil folder
on the Windows 98 Second Edition CD.
2. Right-click MAPC_OFF.INF
-or-
Hold down the SHIFT key and press F10.
3. Choose INSTALL to create the entry for MapCache.
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MAPC_ON.INF - ENABLE MAPPING OF CACHED PAGES
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Refer to the previous section for information concerning the mapping
of cached pages.
Windows 98 will map cached pages if the entry for MapCache is
absent.
To remove the registry entry for MapCache:
1. Select MAPC_ON.INF in the \Tools\MTSutil folder
on the Windows 98 Second Edition CD.
2. Right-click MAPC_ON.INF
-or-
Hold down the SHIFT key and press F10.
3. Choose INSTALL to remove the entry for MapCache.
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