OSOTMEM1 - OS/2 ADDRESSING MEMORY GREATER THAN 16 MB
01/26/96

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     OS/2 Addressing Memory Greater Than 16 MB--All OS/2 Releases
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Please Read Entire Document for Full Explanation of Procedures
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DESCRIPTION

This document provides information about how OS/2 addresses memory 
greater than 16 MB.

RESOLUTION

OS/2 attempts to address all RAM directly, but can be limited by device 
drivers to addressing only 16 MB. OS/2 queries loaded device drivers to 
determine if a given device driver can access more than 16 MB of RAM. 
If any device driver returns that it cannot address more than 16 MB, 
OS/2 directly addresses only 16 MB of RAM. RAM above 16 MB is reserved 
for an in-memory Swapper, which is used before SWAPPER.DAT is used. If 
NOSWAP is set in the MEMMAN statement, the in-memory Swapper is not 
disabled. The call used to query the device drivers is a DOSDevIOCtl, 
Category 8, function 63h API call.

A device driver might not be able to address RAM above 16 MB because:

* The device driver is a block device driver, which uses DMA, whose DMA
  channel is only 24 bits, and the device driver was not programmed to
  work around the DMA's limitation of addressing 16 MB of RAM.

* The greater-than-16-MB bit in the device-driver attributes returned
  from the API call is not set.

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