Storage Cost Calculation

Duncan Booth duncan.booth at invalid.invalid
Sun Sep 28 22:07:31 CEST 2014


Steven D'Aprano <steve+comp.lang.python at pearwood.info> wrote:

> The Model B supported more graphics modes, had a six-pin DIN connector
> for a monitor (both the A and B had UHF output for connecting to a
> television, but only the B supported a dedicated monitor), had support
> for an optional floppy disk controller and even an optional hard drive
> controller. It also had RS-232 and Centronics parallel interfaces, a
> 20-pin "user port" for I/O, and even support for a second CPU! The
> Model A didn't support any of those.

I won't disagree with most of those, but the graphics modes were simply a 
function of the available memory as RAM was shared between programs and 
graphics. The model A couldn't do the higher resolution graphics modes as 
they took too much out of the main memory (up to 20k which would have been 
tricky with 16k total RAM).

> At the time, the BBC Micro memory was (I think) expandable: the Model
> B could be upgraded to 128K of memory, double what Bill Gates
> allegedly said was the most anyone would ever need. (He probably
> didn't say that.) So what we need is to find out what an upgrade would
> have cost. 

The memory expansion in the original BBC Micro was mostly ROM. The total 
addressable space was 64k, but 16k of that was the Acorn operating system 
and another 16k was paged ROM: by default you got BBC Basic but you could 
install up to 4 16k ROMs for languages such as BCPL or Logo or to drive 
external processor cards. That isn't to say of course that you couldn't 
expand the RAM: a company I worked for in the 80s that wrote the BCPL and 
Logo ROMs also manufactured a 1MB RAM card with battery backup. 

Later on the B+ had 64k of RAM and the B+128 had 128k of RAM and in each 
case the additional RAM was paged in as necessary but I don't think the RAM 
in the B was ever expandable.

-- 
Duncan Booth



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