FPGA VAX update, now DIY TTL computers

[Tony Duell]

> 
> How does parity memory work?  Must one use the extra bit for parity or 
> could one use it as a ninth data bit?

Genuine parity memory does, indeed, store 9 bits, and you can use it as 9 
bit wide RAM. Certainly some of the old 30 pin SIMMs were genuinely 9 
bits wide.

There was a hrrible thing called fake parity memory. It stored 8 bits and 
calaculted the parity bit on a read (ignored the incoming parity bit on a 
write) to keep the memory controller happy. Of course you can't store 9 
bits in that type of device.

-tony