in a very simplistic explanation
Computers work at different hardware layers.
"BIOS level" is responsible for the ram slots, you see this during the post test where it reports how much ram you have.
Windows works the next level up, it doesn't know or care about slots, how much is on each stick, speed, etc, all it does is ask bios how much ram is available.

So no it's not possible to tell windows to only look at the first slot, you would have to do this in BIOS and don't think any BIOS has this feature.

It's typically considered best practice to put ram in descending order, I've never looked into how much of a difference this really makes though.

you could try to install a Ramdisk in W98, so there will only the remaining RAM visible to the OS.
selecting the Ramdisk for the W98 swapfile could even speed up the installation.

Greywolf1 wrote on 2024-07-03, 20:07:

Question about ram I’ve got mis matched pairs of ram 2x 512mb and 2x 1gb and 4 slots on motherboard. Is it possible for win 98 t […]
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Question about ram
I’ve got mis matched pairs of ram 2x 512mb and 2x 1gb and 4 slots on motherboard.
Is it possible for win 98 to focus on the one stick while xp sees all of it.
Not sure how it works if you can get it to focus on the first slot or not. Or if you have install ram in descending order.

If you're just trying to limit the ram to under 512mb, there's a setting in the system.ini posted in a lot of places online including here somewhere.

RAM disk sounds to complicated for me and don’t fancy breaking my ram.
Think the remaining options are ram swap or limiting or mempatch max mem.

Cheers for advice