Microsoft KB Archive/66685

MSDiag: Description of the Memory Information Displayed PSS ID Number: Q66685 Article last modified on 11-27-1990 PSS database name: PSS

1.00

MS-DOS

Summary:

Microsoft Diagnostics displays information about the different types of memory detected. The following describes values displayed.

More Information:

Total
The amount of base conventional memory present on the computer.

On some early PC models, the amount of conventional memory detected is controlled by the settings of the dip switches on the system board and may not reflect all the memory that is physically present.

Available
The amount of free conventional memory.

EXTENDED (NON-XMS) MEMORY
The amount of extended memory present on the computer.

Extended memory is memory at addresses above 1 MB, which can only be accessed on an 80286, 80386, or 80486 CPU running in protected mode.

LIM Version
The version of the Lotus/Intel/Microsoft (LIM) Expanded Memory Specification (EMS) that an expanded memory manager supports, if one is present.

If no expanded memory manager is present, Microsoft Diagnostics will display a value of 0.00. The EMS defines a hardware/software subsystem that allows applications to access bank-switched RAM. LIM version 3.2 will allow access of up to 8 MB of bank-switched RAM, version 4.0 of the specification supports access of up to 32 MB of bank-switched RAM.

Page Frame Address
The segment address in hexadecimal of the start of the page frame used by the expanded memory manager.

If a page frame is not present, Microsoft Diagnostics will display “Not detected” for this value. If a page frame is present, it will also be shown in the visual memory map with the letter “P”. The page frame is a 64K address area that is used to map expanded memory pages into the physical memory space of the CPU.

Total(XXXX Pages x 16K/Page)
The total amount of expanded memory present in the system.

The value XXXX is the total number of 16K expanded memory pages.

Avail(XXXX Pages x 16K/Page)
The amount of available expanded memory present in the system.

The value XXXX is the number of available 16K expanded-memory pages.

XMS Version
The version of the Extended Memory Specification (XMS), if one is present.

If no extended memory manager is present, Microsoft Diagnostics will display a value of 0.00. The XMS defines a way for applications to access extended memory on 80286, 80386, and 80486 machines.

Driver Version
The internal version of the extended memory manager, if one is present.

If no extended memory manager is present, Microsoft Diagnostics will display a value of 0.00. The extended memory manager is a device driver that implements the XMS.

A20 Address Line
The current status of the A20 address line.

When the A20 address line is enabled, the 64K area above 1 MB (also known as the High Memory Area, or HMA) becomes addressable by the CPU while still in real mode.

High Memory Area
The current status of the High Memory Area (HMA), the 64K area above 1 MB.

If the HMA is present and currently unused, Microsoft Diagnostics will display “Available”. If the HMA is being used or if there is not an extended memory manager present, Microsoft Diagnostics will display “Not available”.

Available
The amount of free extended memory available to applications through the extended memory manager.

Largest Available Block
The size of the largest free extended memory block available through the extended memory manager.

Copyright Microsoft Corporation 1990.