Re: faster CPU and the Lisa OS

The original 16 MHz XLerator's timing interfered with reading the serial number from the video stream, which the Lisa OS isn't happy about. I believe this problem was fixed in the 12.5 and 18 MHz XLerators but have not verified it.

The bigger issue is Lisa's MMU. Most of the speed gain of the XLerator comes from having RAM on-board (that the CPU can access with zero wait states). However, this means not going through the MMU on the CPU board.

We haven't studied how the Lisa Office System and Workshop use the MMU. To the extent that memory is moved around with the MMU during operation, this would be a difficult problem to address.

It may be the case that LOS doesn't actually move some portion of memory and the XLerator memory could be configured in a way that LOS (and other operating environments such as Xenix and the Workshop) would be able to use the fast RAM and be unaware that the MMU was being bypassed for some portion of the address space.

If that is the case, then it is conceivable that there could be a "pre-boot" floppy disk that would configure the XLerator 12.5/18 in such a way that LOS would boot, work properly, and derive some benefit from the XLerator.

So, it may be possible, but it isn't quick and easy.

>Something I've always seen mentioned with the CPU upgrades that are
>available for the Lisa is that they are not compatible with the
>original Office System. Why is that? Would it be possible to get a
>"hopped up" Lisa running the Office System? I would think that a
>slight boost in speed would make it much less laggy.

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