Date   : Wed, 15 Apr 2015 09:52:34 +0100
From   : jumbos.bazzar@... (Mark Haysman)
Subject: EPROM versus ROM for BBC/B OS1.2

>> Some incompatibility between the hardware and OS1.2?
> Fitted with Data-Center, so board was modified so that 2 ROM sockets are
> seen as 3 each and another for 1 RAM
> if I remember correctly.
>

Hi. I make the DataCentre, and do the mods to the Beeb you have.

There are three modified sockets, the far right one is for a 32K RAM chip, 
so pin 27 is connected to a /WR line across the board. The next two are 
modified to take 27512s, so can have 4 ROM images in each position. The 
modified sockets are backwards compatible to 27256 and 27128.

You shouldn't have any compatibility issues using faster ROMs in the Beeb, 
I've used Atmel 45ns access chips with no reliability issues at all.

Mark.