Mac Plus Memory Mods

[Aoresteen]

We all know that the Mac Plus will boot with 512K, 1 meg, 2.5 meg, or 4 megs of RAM. How about 256K or 128K?

If I took a couple of 256 K 30 pin sims and cut the high address line, will it cut the memory seen in half? In otherwords, can I mod a 256K SIM to get 128K or 64K of RAM?

If so, then by placing two modded SIMS we could get a 256K or 128K Mac Plus.

Why? Just for fun or to test software in a 128K environment using a Plus.

I wonder what the Plus ROM would do on startup if it found 128K or 256K of RAM? Would it error out or continue to boot?

If you can use a 64K or 128K SIMM, the different memory capacities of a Mac Plus would be:

128

256

382

512

640

768

1024

2048

2176

2304

2560

4096

I bet that will confuse some older software 8-o

 

[Mac128]

See this:

http://68kmla.org/forums/viewtopic.php?t=2882

and this:

http://68kmla.org/forums/viewtopic.php?t=2435

 

[trag]

Hmmmm. That would be an interesting experiment. I've been keeping a 512KE around, more or less just because it will run Megaroids and a Plus or later will not. But if I could make the Plus run Megaroids just by installing smaller SIMMs...

Well, I couldn't bear to get rid of the 512KE, but it could go into longer term, less accessible storage.

 

[Mac128]

I've been keeping a 512KE around, more or less just because it will run Megaroids and a Plus or later will not.

AFAIK, there is no difference between 512Ke & Plus that would prevent software from running except for the RAM. Since you can easily turn a Plus into a 512Ke, you have no need to worry about upgrading to a Plus.

However, if you are like me, you want to keep that original case design. Look for a DOVE MacSnap SCSI upgrades which turn up from time to time on eBay and add SCSI to that 512Ke. You can also add RAM, but that would defeat your desire to run Megaroids.

 

[trag]

AFAIK, there is no difference between 512Ke & Plus that would prevent software from running except for the RAM. Since you can easily turn a Plus into a 512Ke, you have no need to worry about upgrading to a Plus.

Ah, I think you misunderstood me because I was not very clear. I have a Plus and a 512KE (and a few others, of course). I mainly keep the 512KE accessible because of the Megaroids issue. If the Plus would run Megaroids with 512K or less installed, then I could pack the 512KE away somewhere less accessible and just keep the Plus where I can reach it.

It is not a question of whether to modify a single machine, but rather a matter of space from keeping two similar machines with one key difference.

 

[Aoresteen]

Reading the links Mac128 provided, 128K SIMMS do not exist. And if you mod a 256K SIMM you will get 1/4 the capacity or 64K.

So assuming I can MOD a 256K SIMM to 64K, here are the possible capacities for a Mac Plus:

128k

256k

512k

640k

1024k

2048k

2176k

2560k

4096k

So a 256K Mac Plus is possible in theory (four 64K SIMMS) as is a 128K (two 64K SIMMS).

Now I have something to do with my box of 256K SIMMS (if I can find them!)

 

[Aoresteen]

Also, I remenber a DA that let you reduce the amount of memory in a Plus. Or maybe it was an app, i'm not sure.

Anyone remeber it? It would date from 1985 to 1987 or so.

 

[Mac128]

This may be helpful reading as well:

http://68kmla.org/forums/viewtopic.php?t=2042