🚀 go-pugleaf

salmassr@oiscola.Columbia.NCR.COM (Samer M. Almassri) writes:

>Hi.  I always get confused between expanded and extended memory.
>Could anyone post or mail me a good explanation.

I guess I can't complain about the number of times this has been discussed,
I asked exactly the same questions when I first started using the net.  So
here goes the regurgitation.

>1- What is the difference? (Technically & from a user point of view)
Extended memory (XMS) is directly addressable by the CPU.  Only 80?86 cpu's
are capable of accessing XMS (ie if you have an 8086 or 8088 then forget
about XMS).
Expanded memory (EMS) is a cludge used to give the poor old (decrepid sp?)
8086 and 8088 processors access to more than the 640K they normally have.
NOTE - the 808? processors are able to address 1024K directly, but the
memory above 640K is used for things like video cards and other configuration
stuff.  64K of this stuff is used for EMS.  Basically all that happens is
that you have all of this EMS memory sitting on its own card and you have
a driver that swaps it in and out of this 64K block.
As you can imagine, this makes EMS a little slower.

>2- Why there are two kinds?
XMS because as processors got bigger, they wanted to address more memory.
EMS because as programs got bigger, they wanted to address more memory, and
people didn't want to get a better machine with a better OS.

>3- Which one you should use?
This depends.  If you have a 808? then EMS is all you can have.  If you have
an 80?86 then it still depends.  EMS is slower than XMS, but appears to have
a lot more support than XMS.  There is a trend I think of late, to support
both EMS and XMS.  For example, windows 3 supports both (in fact it's XMS
support is better than its EMS support methinks).
You can get cards which can be configured both as EMS and XMS or a bit of
both, which brings me to ;

>4- Can the computer use expanded and extended memory at the same time?
>and other related information that you can think of...
Yes you can.  The boards mentioned above make this quite easy.  In fact some
80?86 mother-boards have switches on them that allow you to configure your
memory in this way.

I hope that this all helps.

>Thanks in advance...

> __________________________________________________________________________
>|   _____   ______           _____  _____     Imagine Life in a Peacefull  |
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>| |____   /_____/ /  \ / / /---   /____/  O  O                             | 
>|      | /     / /      / /      /   |    \__/       Samer M. Almassri     | 
>|\____/ /     / /      / /____  /    |   salmassr@oiscola.columbia.ncr.com | 
>|__________________________________________________________________________|

ant

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 -O-  Anthony Murdoch           Prentice Computer Centre
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