second thoughts on buying a 3000UX
Dave Haynie
daveh at cbmvax.commodore.com
Tue Mar 12 07:23:10 AEST 1991
In article <19512 at cbmvax.commodore.com> jesup at cbmvax.commodore.com (Randell Jesup) writes:
> Note: I haven't measured these things, I'm going on reports from IBM-
>types about the number of wait-states to access video ram (I've heard numbers
>as high as 12).
Dr. Dobbs had an in-depth article on these VGA toys a few months ago. They
had PC-AT bus wait-states in the 20-30 range, which would translate to a mean
of 12 XT bus wait-states, to VGA memory. The other interesting thing about
the VGA register set is that everything is intrinsically 8 bits wide. So you
don't get an AT bus version of a VGA card for its bus width, but generally
because the board runs at AT bus rates (4 cycle 8MHz clock) rather than XT bus
rates (4-5 cycle 4.77MHz clock). There are a number of non-standard additions
to VGA boards that gives you a more reasonable CPU to memory bandwidth, but
to use such features requires special code; a generic VGA-X wouldn't do much
for you. This architectural ugliness accounts for the big speedup IBM is
claiming with XGA, even though VGA and XGA use the same generation memory.
>Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
--
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
{uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy
"What works for me might work for you" -Jimmy Buffett
More information about the Comp.unix.amiga
mailing list