knudsen@ihwpt.UUCP (04/10/87)
It should be possible to extend the Coco 3 to 2 Meg of RAM.
It's easy for Tandy to extend the architecture itself in
a redesign.
It may even be possible to do it yourself with a plug-in
daughter board.
Reason: The GIME's DAT registers, which hold the upper addressing
bits for the memory map, are defined as only 6 bits each.
But they're on an 8-bit bus -- each memory address is one byte
or 8 bits. So conceivably the upper 2 bits, currently unused,
could also be appended to final physical addresses to get
a total of 8+13 = 21 bits = 2 Meg.
Not that the current hardware would do it alone.
The upper two bits may not be physically implemented inside
the GIME chip. Or there may be no way for them to get out
as additional address bits. But of course Tandy could redesign
the GIME to do this. Only one extra output pin would be needed--
it would supply a 9th address bit to the DRAMs during both
RAS and CAS, which is how some 1M x 1-bit DRAMs work.
(Remember the Coco3 uses two interleaved banks of 256x1 DRAMs
for 512K, so 1-Meg chips would give 2 Meg).
Instead of waiting for Tandy (and Social Security),
someone could make a daughter board that plugs into the
existing GIME socket (some plug, that) and mounts the GIME
plus a few extra chips to capture the two high-order DAT
bits and put them out to the other daughter board with
the 16 1-Meg DRAMs. (The latter may be just the 512K
board we're using today).
I'm sure OS9/2 could handle the fourfold increase in
RAM blocks. Right now I'm a long way from using up
512K, but hey, let's look ahead!
PS: Alternately, you could use the extra two bits by
right-shifting the present addresses and still have just
512K, but in smaller blocks of 2K instead of 8K.
Or, 1 Meg of 4K blocks. Or 4 Meg of 16K blocks.
Several tradeoffs possible....
"Don't tell me -- OS9/2 is from outer space!"
"No, it's from Iowa. It just works like outer space!"
--
Mike J Knudsen ...ihnp4!ihwpt!knudsen Bell Labs(AT&T)
Delphi: RAGTIMER CIS: <memory failure, too many digits>
" ~E(x):[is_lunch(x) && cost(x)==0] "jimomura@lsuc.UUCP (04/15/87)
While Mike is working on the main RAM, I've been thinking about RAM disks. Actually, more than just that, I've been thinking about my current system configurations in general and planning for the summer. I currently have my ST running OSK version 1.2 and (big drum roll please ... ) my QT-20X 68020 machine (yup, it arrived last week and I've already started to used it), both with 20 Meg. hard disk systems. I'm starting to dread my CoCo3 with its slow and now, relatively small capacity floppies (gee whiz, only 80 cylinders, single sided per drive?). I'm not entirely happy with hard disks. I find the noise annoying. I'm thinking about networking everything to the QT and sticking the QT in a closet. So, how about RAM disks for the CoCo? Has anybody used the Disto RAM disk under Level II? That seems like a nice idea. Cheers! -- Jim O. -- Jim Omura, 2A King George's Drive, Toronto, (416) 652-3880 ihnp4!utzoo!lsuc!jimomura Byte Information eXchange: jimomura