EMS memory for 3-S under Windows 95/98/2000/XP

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Configuration of EMS memory

if EMS is not installed, or the MS-DOS window is not set up to use it, you will get a system message "No EMS card/driver or no pages free". If the EMS driver is not configured to provide enough memory, 3-S programs (such as LOCDIG, SSV, TRCPLOT, or BASEPLOT) may not be able to handle large raster files.

" Expanded" memory was used by 16-bit MS-DOS programs to overcome the memory limitations imposed by a MS-DOS's effectively 20 bit address space and the memory model used by Intel 80386 and 486 chip designs. Memory from outside the "real" 1Mbyte address space imposed by MS-DOS is swapped in and out in 16kbyte "pages", as required, using a 64kByte page buffer. In a "real" 80386 type MS-DOS system, this memory came from the pool of up to 16MBytes of real "Extended" memory allowed by the 80386 chip, which ran in "real mode"

On a Windows 2000/XP system, MSDOS runs in a window which behaves like a virtual MS-DOS PC. This isolates the memory used by programs running there, so that a "crash" in the program will not generally crash the Windows operating system (unlike Windows 3, which ran in "real" mode). Windows 95/98 is a hybrid which provides some protection against programs corrupting the whole system, but which is still vulnerable, because programs share the same real mode MS-DOS kernel.

Windows 95 / 98

The EMS driver is called by the MS-DOS command processor Command.com to provide 64kbyte pages of RAM from the Windows operating system memory pool (which may contain many megabytes of spare memory).

When an MS-DOS window is started, COMMAND.COM is executed. You can check whether EMS is installed by right clicking on the title bar of the window and selecting "properties"

Screen dump of MSDOS properties

On most PCs running Windows 95 or 98, COMMAND.COM in will be in the C:\WINDOWS, but sometimes there will be an additional copy in the root directory C:\. Select the "memory" tab.

Screen dump MSDOS memory setup

You should set the EMS memory to the minimum required by the MS-DOS programs that you are going to run. Remember that while the MS-DOS window is open, the EMS memory allocated will not be available to other windows. Note that the maximum for EMS memory is 16.384 Megabytes.

Before you can allocate EMS memory in this way, an EMS driver must be installed on the system. The default Windows 95/98 setup installs the driver, but some program installations (Novell Netware client for example) may make it necessary to provide an EMS driver at startup. To install the drivers, add the following to lines to the file CONFIG.SYS in the C:\ root directory :-

DEVICE=C:\WINDOWS\HIMEM.SYS
DEVICE=C:\WINDOWS\EMM386.EXE

You will need to re-boot the computer before the changes can take effect.


Windows 2000 / XP

The configuration for the MS-DOS window's memory is determined by the file _Default.PIF. This will be in the Windows system directory, i.e. C:\WINNT or C:\Windows. Right click on this file and select properties|Memory. Set the EMS memory parameter to 4096 to allocate 4MBytes of EMS memory whenever an MS-DOS window is invoked.

Note that, unlike for Windows 95/98, you DO NOT have to install EMM386.exe, because the system is already running in "virtual" mode and provides the necessary memory management itself.

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