CONFIG.SYS

Virtual device drivers utilized by VDMs consume very little or no memory below the 640KB limit. These device drivers reside outside the V86 mode address space. However, a user may install device drivers that are required by and are specific to certain applications which will run in a VDM. If the commands to load these device drivers (or other memory-resident programs) are added to CONFIG.SYS, these device drivers (or programs) will be loaded into every VDM when it is created, and will reduce the amount of conventional memory available to DOS applications in every VDM. To ensure the maximum amount of memory is available in each VDM, it is recommended that:

DOS device drivers specific to a particular DOS application should be loaded via the DOS_DEVICE option of DOS Settings. DEVICE= statements for DOS device drivers should be eliminated from CONFIG.SYS unless the device driver is required for every VDM.

The number of buffers specified in the Buffers command in CONFIG.SYS should be minimized. Each buffer consumes about 500 bytes. Be careful to not reduce this number too much because some programs might not run properly if there are too few buffers. The default number of buffers is 30; the number should not be reduced to fewer than 10 or 15 buffers.

If CONFIG.SYS includes the LASTDRIVE command, this should be set to a letter such as J or K, rather than Z. Each additional drive uses about 100 bytes.

If the CONFIG.SYS file contains an FCBS command, set FCBS to 1.

The order of the DEVICE and DEVICEHIGH commands in CONFIG.SYS is important since it can affect both the efficient use of memory and the proper operation of the various programs started from CONFIG.SYS.

The CONFIG.SYS statements and options related to VDM operation, and which can be selected during installation, are shown below:

Load the DOS Command Interpreter and load it resident into memory

SHELL=C:\OS2\MDOS\COMMAND.COM C:\OS2\MDOS /P

DOS=HIGH, UMB

DEVICE=C:\OS2\MDOS\ANSI.SYS

DEVICE=C:\OS2\MDOS\VEMM.SYS

DEVICE=C:\OS2\MDOS\VXMS.SYS /UMB

DEVICE=C:\OS2\MDOS\VMOUSE.SYS

DEVICE=C:\OS2\MDOS\Vxxx.SYS

VCGA.SYS (if CGA or EGA w/ 64KB)
VEGA.SYS (if EGA w/ 128KB)
VVGA.SYS (if VGA or 8514)
V8514.SYS (if 8514)

DEVICE=C:\OS2\MDOS\VCOM.SYS

The following list shows the order in which device drivers should be specified in CONFIG.SYS:

VEMM.SYS
Any device drivers that use expanded memory
VXMS.SYS
Any device drivers that use extended memory
Any device drivers that use upper memory blocks.
This is the optimal order in which the CONFIG.SYS file should start device drivers. Whether these statements are included at all depends on the amount of memory installed, the hardware configuration, and on the DOS applications to be run.
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