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Full Version: 9825 A vs B
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I'm wondering what all the differences are between the 9825A and the 9825B.

The one thing that I can see that is obvious is that the B has a built-in ROM OS and the A has a slide in Module.

Is this the only difference?
What are the other differences?

I believe the -A could take either 8K(byte) or 16K byte RAM boards, with a maximum of 2 boards (any mix). This limited you to
32K bytes RAM, but if you had that much you couldn't use some of the plug-in ROM modules. So 24K was a more practical limit.
The -B has 1 memory board with 32K RAM, the system ROMs and most of the plug-in ROM functions on it. You can add a second special
32K RAM board, for a total of 64K RAM (not all of it is available, you get about 61K bytes free at power-up) _and_ virtually all the option ROMs.
I think the only ROMs not built-in are the Matrix ROM and the Floppy Disk ROM, and both of those can be added in the front-port connectors as usual.
Apart from the different memory boards, there are couple of track cuts on the CPU board in the -B to disable some of the address decoder circuitry on that board.
I may have got the suffix letters mixed up, but I know there is a 9825 with 64K RAM and almost all the ROMs built-in -- I have one. And I know that earlier models
have the system ROM module on the RHS of the machine.