Bank-switchable memory for the Altair 8800

[Wayne Parham]

What's the best memory board for a banked-memory Altair?

I'd like to create a version of CP/M 3 that supports the IDE drive and banked memory. Right now - without banked memory - TPA is 47Kb. I think that could be bumped up 8Kb or so with maybe a 48Kb swappable bank.

Seems like a Cromemco memory would be great, but I think those things are probably pretty rare. I think it would be useful to have a memory board with 112Kb and a dip-switch configurable bank-control port address. Bottom 48Kb is bank-switched, and top 16Kb is common. Maybe even give it additional provisions to swap out boot ROM up top too.

I've seen larger memory boards than this for S100 systems, but most seem to favor a flat address space for use with processors made after the 8080. I'm not really interested in that 'cause the original 8080 can't use the extra memory. But a switchable pair of banks to swap out portions of the operating system to make room for transient programs would be great.

[AltairClone]

A couple of 16K bank boards along with a 64K board like the RAM17 would work. Put the 16K boards at 8000-BFFF and put a hole there in the RAM17.

The Cromemco 16K boards will work. I have a DRC 16K board that also supports bank switching- I’m sure there are many others but I have not researched it to this point.

Mike

[Wayne Parham]

I think all of those would be good options and I have a ton of 2114 chips so I would be happy to use boards that used that chip. I noticed that's the case for some of the old 16Kb static RAM boards.

But aren't old memory boards like that kind of hard to find? I did a quick search for the DRC, CompuPro and Cromemco boards and found lots of documentation but none for sale. Seems like eBay is so spotty on old S100 boards.

I was kind of hoping to find a new S100 memory board design that would work for this application but those are kind of rare too.

[AltairClone]

North Star RAM boards support bank switching too.

[toml_12953]

A couple of 16K bank boards along with a 64K board like the RAM17 would work. Put the 16K boards at 8000-BFFF and put a hole there in the RAM17.

The Cromemco 16K boards will work. I have a DRC 16K board that also supports bank switching- I’m sure there are many others but I have not researched it to this point.

Mike

Does the RAM 17 work with a front panel, though?

[AltairClone]

Yes, the RAM17 has DIP switches to enable front panel compatibility.