PRB: PCMCIA Memory Window Size Limitations

• Microsoft Win32 Device Driver Kit (DDK) Windows 95

SYMPTOMS

Windows 95 may not successfully allocate large memory windows to PCMCIA cards on machines containing 16MB or more of RAM.

CAUSE

PCMCIA devices are subject to the ISA bus address restriction of 20 bits or 16MB. If a machine has at least 16MB of RAM, the PCMCIA memory window must then reside between 640KB - 1MB.

Depending on the machine configuration, Windows 95 may not be able to provide large PCMCIA memory windows. For example, on many machines memory windows of 64KB or larger may fail. Even smaller windows may fail depending on the machine configuration.

RESOLUTION

It may be advantageous to create multiple logical configurations, each with a progressively smaller memory window all the way down to 4KB. The driver can then take advantage of the larger memory window if it is available, and can still work even if only a small memory window can be allocated.

MORE INFORMATION

See the Windows 95 DDK for more information on PCMCIA.

Keywords :
Version : 4.0
Platform : WINDOWS
Issue type :