🚀 go-pugleaf

in article <1741@calvin.cs.mcgill.ca>, depeche@quiche.cs.mcgill.ca (Sam Alan EZUST) says:

> In general, computer specific hardware addons will be a thing of the past.
> I mean, shit - if we have a DMA port which can transfer data at 10
> megabits per second on our old clunking 1040sts, guess how obsolete a
> card slot which works with IBMs will be (I wish I had some numbers, but
> I bet that those card slots in the IBMs aren't much faster if they are at
> all).

The PC-AT bus at 8MHz has a maximum bandwidth of 4 megabytes/second.  Of course,
since it doesn't permit true DMA bus masters (it has a DMA chip for faster-than
CPU transfers, in theory, but in practice the DMA chip is slower than the CPU for
such transfers), the effective maximum rate on the bus is 2 mb/sec.  For an
8 bit card on that bus, you're down to 1 mb/sec, and if it's run at PC-XT
speeds, that's down to less that 512 kb/sec.

The Amiga bus runs at 7.16MHz, for a corresponding bandwidth of roughly 3.75 
mb/sec, which can be a bus-mastered transfer (most hard disks work this way).
That's not fast enough, but it's decent for many things.

For an asynchrous SCSI disk transfer, you probably wouldn't notice much
difference in raw transfer speeds between the DMAed Amiga, CPU copied IBM,
or DMA chip driven ST; the SCSI's upper limit is 1.5 mb/sec in all cases.
However, the Amiga would spend less time in the actual transfer, so there'd
be more CPU time available for other things.  So, in general, faster bus
access buys you bandwidth.  Even if you can't think of anything that
actually needs that bandwith, you'll get CPU cycles out of it.

> The only things we would need slots for nowadays is for accelerators,
> graphics enhanceors, and perhaps emulators. 

They always say you won't need more slots this time, because in general,
every time a real new computer comes out, all the stuff you put in the
slots of the previous generation are now on the motherboard.  So in 
the 70's you wasted a slot for a floppy controller, in the early 80s
you wasted a slot for a hard disk controller, and now both of those 
are built in.  But still, someone's going to find a use for as many
slots are you give them.  Just ask Apple -- they were the last ones to
think they'd taken care of everything, first in the Mac and then the
Mac Plus.

What goes in those slots is about 1/2 constant, 1/2 changing.  The 
constant 1/2 is the thing that'll never be popular enough for standard 
equipment on your machine, such as a special purpose data aquisition 
board, 8 extra serial ports, superhires graphics board, etc.  These 
things have always been around, always will be.  The second 1/2 is
the "move against obselence" stuff.  Open slots let you add those
floppy controllers in the 70's and hard disks in the 80s without
throwing out the whole machine.  This kind of thing will probably be
less and less common, because the average person's need for any level
of computer power won't forever be growing unbounded.  Human nature
will set an upper limit on how much you need here.  We're not there
yet, so this kind of slot still makes sense.

I've got every slot in my Amiga 2000 here filled with something.  I
just had to throw out 2 megs of RAM out of the machine to fit the 
ethernet card.  

>  S. Alan Ezust aka "Depeche Modem"       depeche@calvin.cs.mcgill.ca
-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
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                    Too much of everything is just enough