Amiga 3000UX, X, OpenLook, Motif, Color, A2410, Etc. (somewhat long)

[Dave Haynie]

In article <1991Mar20.100122.1717 at kessner.denver.co.us> david at kessner.denver.co.us (David D. Kessner) writes:
>In article <19986 at cbmvax.commodore.com> daveh at cbmvax.commodore.com (Dave Haynie) writes:

>>The A3000 was designed from the ground up as a high performance multitasking 
>>personal computer.  That is something different than a high performance single
>>tasking computer, like your typical '386/'486 system, or most Macs.

>Please elaborate.  My 386 UNIX box does quite well being a "High performance
>single tasking computer".  

That is exactly what I claimed.  I suspect you meant to say that it worked well
as a high performance multitasking computer, and then go on to discuss I/O in
a single tasking mindset:

>I/O speeds are not really a problem since only very high-end disk drives get 
>more than 2meg/sec of the 8mhz I/O bus, and since I run mine at 12mhz there 
>is no shortage of bandwidth.  

There certainly is if you're multitasking.  The typical PC bus disk interface
is a PIO (programmed I/O), non-DMA, 16 bit device.  Since you can run at
faster bus speeds in many cases, and have a cached high speed CPU to do the
data moves, you don't use the bus resident DMA controller, and that's good. 
You can probably transfer about 3-5 MB/s between the jazzed AT bus and main
memory, depending on your memory and all.  Fine for single tasking, you are not
going to find single hard disks that exceed that rate.  However, the CPU does 
have to be involved in that transfer, and in many cases sits around in a 
tight PIO loop for the duration of transfer of an entire block or more.  In the
A3000, you get 32 bit wide fully buffered DMA from SCSI.  Again, your single 
disk isn't likely to exceed 2 MB/s.  However, since after setting up a 
transfer, the CPU doesn't get involved again, and since the hard disk DMA
controller always runs full speed cycles at 20 MB/s, you use at most 10% of
your machine's bandwidth in a full speed transfer.  This leaves 90% available
for running other tasks, rather than the 0% available during a tight PIO loop.

>Comparing the 030 with the 386 might be seen as a little skwed, and it is.  
>But when the A3000UX comes in at HALF the speed of the 386 then it raises 
>more than an eyebrow...

It is a foregone conclusion.  All things being externally equivalent, the 
'030 and '386 are pretty comparable.  However, when you compare the uncached
'030 (A3000 or NeXT) against a cached '386, using a cache-sized benchmark,
you are kind of stacking the deck in favor of the '386.  Not that I have any
problem with the idea of a cache, it certainly will help some.  What you get
here is a best-case estimate of its utility.

>All that you'd really need is a redesigned case and maybe a power supply.
>I'm sure some third party has thought of this...

3rd party tower cases for the A2000 have been around for some time.  Though the
latest news from CeBit might make the market for an A3000 tower case a bit
less attractive...

>Sorry.  I was in that C-64 mode for a sec there.  You remember, where the CPU
>was practically resonsible for shifting in the bits in from the user port.

Actually, completely responsible.  The C64 has a software UART, plain and 
simple.  One port line for transmit, one for receieve, more for handshaking
and all.  Using all the available CPU power, you could run a reasonably good
1200 baud VT100 emulation with it.  It did the floppy disk stuff the same 
way, albeit via a software generated synchronous serial port.  

>I should say a faster UART, perhapse with a FIFO.  Like the 16550...

FIFO would be a good idea.  I would really like to see the UART redesigned
to use video line DMA, like the floppy does.  So you get a pretty much 
unlimited buffer.  Convincing the chip designers may take awhile on that one...

>David Kessner - david at kessner.denver.co.us            | do {


-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
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	"What works for me might work for you"	-Jimmy Buffett