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SUMMARYWindows 3.0 can access up to 16 megabytes (MB) of physical memory. With the release of version 3.1, Windows can access more than 16 MB of physical memory. This article discusses the factors that influence the amount of memory available to applications in the Windows environment. MORE INFORMATION
In enhanced mode, Windows versions 3.0 and 3.1 can use features of the
Intel 386 (and compatible) microprocessors to supplement the installed
physical RAM memory with virtual memory in a disk-based swap file. As
physical memory fills, Windows sends the least-recently used pages of
memory to disk. When this data is later accessed, Windows pages it
back in from disk. This activity is transparent to applications in the
system.
While the About dialog box in the Program Manager reports an estimate of the amount of memory available, Windows does not maintain sufficient information to accurately report the amount of free memory at any given time. Maintaining more accurate information regarding the amount of free memory would seriously degrade system performance because memory is allocated and freed very frequently. The values reported by the GetFreeSpace and GlobalCompact functions are less than or equal to the amount of free memory available in the system. Because of their imprecise nature, an application should use the value reported by one of these functions only for an informational display. The application must not assume that it is possible to allocate that much memory. The largest block of memory that an application can allocate is affected by the degree of memory fragmentation. Memory available in fixed portions of memory may be available for allocation only as a fixed block. For example, consider the case where the GetFreeSpace function returns 100K available, and 64K of the available space is located in the fixed portion of the heap with the remainder in the movable and discardable portion of the heap. An attempt to allocate a 100K block of movable and discardable memory will most likely fail. Additional query words: no32bit 3.00 3.10
Keywords : kb16bitonly |
Last Reviewed: November 4, 1999 © 2000 Microsoft Corporation. All rights reserved. Terms of Use. |