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Tertz wrote:

Win98+DOS machine.
As I understand Win98 and its applications feel better (or not worse) with 512 mb. But what is with DOS?
Is there any compatibility (or other) benefit to use 128-384 mb instead of 512 for DOS applications?

I thought DOS simply ignored anything over 64MB (I certainly don't remember ever having had any problems using DOS bootdisks on systems that had over 64MB RAM installed, but I'm not really a DOS specialist 😜 ).

If I am not mistaken,
Dos 6.22 will accept only 64mb even if you install more.
Dos 7.1 will accept up to 4gb.
Check via MEM command.
Depending on the era of the motherboard it may accept more than 64mb of ram, but will only cache 64mb and may/will slow the computer if more is used.

If it's DOS Pentium 1 MMX machine (or older), don't bother with more than 64mb ram.
If it's Windows 98SE Pentium MMX (or older) machine, more ram than 64mb may slow down the PC (processor) but will help will the speed of the OS.

http://www.pcguide.com/ref/ram/sizeCacheable-c.html

For DOS 6.22, HIMEM will understand up to 64MB of XMS.
And If you want EMS memory, from the 64MB of XMS, up to 32MB of XMS can be (dynamically) allocated by EMM386 to provide up to 32MB of EMM.

I can't think of any standard DOS game/application that would need 32MB or more memory though.

Besides if protected mode DOS extenders are used, the limits don't apply and if they wanted they could use any amount of memory (maybe up to 3GB or so) you have installed.

In DOS, it all depends on your own usage.
DOS doesn't have any kind of background processes or automated settings.
So DOS itself works the same, no matter how much memory you have (the only exception is where you don't have enough memory to load DOS itself).

So it all depends on the applications you're running, and what memory they need/use.
Eg, if you have memory, you can load a diskcache such as smartdrv.
And some applications can use XMS or EMS to improve their performance.
Some applications also need a lot of free conventional memory, so you may need to configure upper memory blocks and load drivers into that region to free up that memory.
There are also applications that cannot work when XMS and/or EMS is enabled...

Back in my DOS days, I had a boot menu which had 6 different configurations, to cater for all my different applications' needs.
The total amount wasn't all that relevant. I don't think I ever ran any DOS software that needed more than 8 mb, or had any benefits from having more.

Personally, in my retro rigs, I have no practical (*) problems in DOS (6.22) with extra memory (a multiboot DOS/XP machine I had in the past had 1GB). It just takes care of 64MB and does not care about anything else.

(*) IE 5.5 for Windows (3.1) does not install, saying "not enough memory", if you have more than 64MB memory physically installed. There is a command switch that disables memory checking, though. I also had two instances of badly written software which does not run, again saying "not enough memory" when even more than 32MB memory installed. Both of these were software created by possible amateurs and controlling some sort of special industrial automation hardware.

Thanks.

James-F wrote:

If it's Windows 98SE Pentium MMX (or older) machine, more ram than 64mb may slow down the PC (processor) but will help will the speed of the OS.

A common Win98 machine implies P2-P3 CPUs, so cacheable RAM problem begins beyond 512 Mb.

It just takes care of 64MB and does not care about anything else.

DOS itself may not "care", but all memory (at least up to 4 GB) is accessible.
I don't think any DOS game requires more than 64MB of RAM, but some of them may still utilize it if available (Quake comes to my mind).

I also had two instances of badly written software which does not run, again saying "not enough memory" when even more than 32MB memory installed.

Aladdin has this bug. I remember I had to allocate big disk cache (SMARTDRV) to leave no more than 32 MB of free memory, and when I upgraded to 128 MB, even that wasn't enough because smartdrv can't use more than 64 MB. But I found a ramdisk driver that could (I don't remember the name).

I think it doesn't matter if you have "just" 128 or 512 MB of RAM for DOS games. You are well past the 32 or 64 MB "comfort zone", so if something breaks with 512 MB, it'll probably break with 64 MB as well.

I've had this problem in the past where I couldn't get DOS to detect over 16mb's on a 512mb rig (solved with qemm anyways), but I can't really think of any real disadvantage that would apply as a general rule. If the application's designed to take advantage of that much ram (say povray), that's a plus. If not, it shouldn't matter, though I can think of a few scenarios where a very poorly programmed application would fail to run adequately (if at all).

Remember that DOS is barely an operating system (cf. Windows). It does no memory management of its own, your applications need to do that themselves. Notwithstanding HIMEM and EMM386 providing services for applications to access memory above 640KB.

So really the question is not how much memory DOS can "handle" (because it doesn't really handle anything), but rather what compatibility issues exist on a per-application basis.