Thanks Jonathan for your msg about OS/2 crash-proof?, on 24
09-24-1994

JP> DR>
JP>   > For instance, instead of having a 4Meg linear virtual address space
JP>   > per process, OS/2 only has a 512 Meg space ...
JP> 

Yes, sorry a typo there.

JP>   BTW, I regard this talk of "only 512Mb" as rather
JP> unrealistic.  The
JP>   people who usually use this phrase forget that any process that
JP>   required this much memory on *today's machines* would be needing over
JP>   480Mb free hard disc space for the swap file.
JP> 

You're confusing physical memory with virtual memory. For
instance, a database manager can allocate a 2 Gig virtual buffer
but not commit it. This 2 Gig buffer maps to a 2 Gig file on disk.
Any attempt by the user program to access a record in this space
will cause an exception, which the database manager will use to
'fault in' the actual data. So, although the application might
never use more than 64Meg of physical memory, it is important to
have the larger virtual memory space.

Also, some operating systems might take it a step lower and do
something similar in order to provide a memory mapped file. Its
not necessary to have enough physical memory to actuall map the
whole file at once, but it is necessary to have enough to
virtually represent the full file in the process' address space.

___
 X KWQ/2 1.2b X "640K ought to be enough for anybody." - Bill Gates, 1981

--- Maximus/2 2.01wb