Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!rutgers!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: A2630 board
Message-ID: <10036@cbmvax.commodore.com>
Date: 7 Mar 90 18:11:52 GMT
References: <1745@crash.cts.com>
Reply-To: daveh@cbmvax (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 33

In article <1745@crash.cts.com> hawk@pnet01.cts.com (John Anderson) writes:

>   Dave, since the A2630 board uses 16 256x4 chips to make 2 megabytes of RAM,
>then(32 bit RAM), then isn't that actually 512K of actual RAM.  

Well, its actually 512K WORDs of RAM, as well as simultaneously being 2 
Mega-BYTES of RAM.  The same number of chips on a 68000 memory board would be
1 Mega-WORD of RAM. 

>Since each "thing" needs 32 bits then that means it can only hold 512 
>thousand "Things" since each one is 32 bits long?  

No.  The memory can still be byte addressed; all 680x0 family CPUs, and most
others for that matter, equate one address with one byte and allow individual
bytes to be addressed.  All the 32 bit bus indicates is how much data can be
read or written in a single cycle; the CPU doesn't have to read or write all
32 bits at once, it just has that option.

>Well, the quesion is, if I buy your 2630 board with the 2 megs on it, 
>expanding my system to 5 Megabytes of RAM (3 16bit and 2 32bit) can I add 
>the two extra megabytes of 32 bit RAM to the 2630 board and map it somewhere 
>else to avoid the 6 megabyte RAM limitation set by the XT Bridgeboard? 

Not on-board; the A2630's built-in memory must be configured as a single
autoconfig unit of either 2 or 4 megs in size.  You could buy a daughterboard
for it, as soon as someone offers one, and put more memory there; the A2630
daughterboard space is above the 68000 memory map.  Though I would expect 
most daughterboard designs to increment in 4 or 16 megabyte chunks.

-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
                    Too much of everything is just enough