Staking RAM to get more on A500?

[wilykat]

There are few upgrade options for A500 and my A500 has an 8MB SupraRAM sidecar. It does have pass through connector for other devices like hard drive. I am wondering if it'd be possible to get another RAM sidecar and add to it? Or is there a limit to max RAM on A500 via that expansion port? I'm using original CPU and have no plan to upgrade the CPU so additional RAM on CPU board isn't likely for me.

 

[ajk]

The 68000 as an address space limit of 16 MB. Some of that is used to interface with the chipset and other peripherals, so about 10.5MB of RAM is the maximum you can have, including chip RAM.

 

[wilykat]

Hmmm thanks. Guess I won't watch eBay for RAM upgrade. The one I have is 8MB and if I got another, I'd be able to add only 2MB. Not really worth based on past eBay listing.

 

[ajk]

Indeed, and you wouldn't even get the 2MB that way. I don't know what you have now in terms of chip RAM, but by expanding that to the maximum of 2MB you'd have 10 total. Beyond the 8MB fast + 2MB chip you can add half or so MB of other memory but that is hardly worth it.

The only way to significantly upgrade the amount of RAM beyond those specs is to also upgrade the processor.

 

[romppainen]

Is there any difference with 68010 then?

 

[fgh]

No, only with a full 68020 or greater.
Even the 68EC020 in A1200 has the same limit (address space).
8mb was usually the max fast mem on a500, but some rare boards can give up to 12,5mb fast. (some of which will not autoconfigure, but require addmem commands in startup-sequence)

edit: And if it wasn't clear before, using a 2mb expansion together with an 8mb one will not work as they will use the same addresses.

 

[whiteb]

No, only with a full 68020 or greater.
Even the 68EC020 in A1200 has the same limit (address space).
8mb was usually the max fast mem on a500, but some rare boards can give up to 12,5mb fast. (some of which will not autoconfigure, but require addmem commands in startup-sequence)

edit: And if it wasn't clear before, using a 2mb expansion together with an 8mb one will not work as they will use the same addresses.

I had 12.5MB (I think) once on my A500

512MB on Motherboard.
4MB trapdoor (Axram). (Yes, It also used Addmem)
8MB A530

The Ram was 1MB Chip via Motherboard cut trace, taken from 4MB trapdoor.

1MB Chip
3.5 Fast from trapdoor
8MB Fast from 530.