PRB: Windows 95 May Fail to Boot Due to I/O Subsystem Failure

This article was previously published under Q225497
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Under some circumstances Windows 95 may fail to boot, and will display the following error message:
Error: An I/O subsystem driver failed to load Either a file in the .\iosubsys subdirectory is corrupt or the system is low on memory.
This problem may occur when all memory below 1MB is allocated prior to initialization of Ios.vxd. Ios.vxd must allocate memory below 1MB for use as real-mode buffers. If Ios.vxd can't allocate this memory, it fails to load, which in turn causes Windows 95 to fail to boot.

Memory below 1MB is typically reserved for components that specifically request it. However, it is possible that Windows 95 will allocate all memory between 1MB and 16MB during initialization, forcing system DMA buffers (which must lie below 16MB) below 1MB, and therefore preventing Ios.vxd from being able to allocate memory below 1MB.
This problem can be worked around by adjusting the maximum cache size allocated by Vcache.vxd. Vcache.vxd allocatesan initial cache size that is no larger than 9MB. Settingthe maximum cache size to less than 9MB also reduces the initialcache size, freeing up memory below 16MB and allowing Windows 95 to bootproperly.

The maximum cache size is set by adding a "maxfilecache" line to thevcache section of System.ini. The following example shows what an entryin System.ini would look like to set the maximum cache size to 6MB:

   [vcache]   maxfilecache=6144				
This is a known problem in Windows 95. It has been fixed for Windows 98.

Article ID: 225497 - Last Review: 10/26/2013 01:39:00 - Revision: 2.0

Microsoft Windows 95

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