> real-life situations, one faster bus is BETTER
than two separate busses.
In the real world there are too many conditions on
things to make general
assumtions that always work.
Including this one, no doubt? ;-)
For simplicity and cost as a generalization
one fast bus will meet those needs and give good performance.
That statement is supported by fact!
Now a counter to that. For error/fault tolerence, and
if the fastest bus
is not fast enough then two (or more) will always win but will not be
cheaper.
I'm not sure I understand this: the fastest bus is not fast enough?
I don't need numbers to prove that, the logic is
deeper.
? Deep sub-micron or something?
To tie that to
the "old" machines they ran their generations PCI and then some. I'll bet
in a year or two you make the exact same arguement about the obsolete PCI
bus.
Gee, as much as folks like to pidgen-hole me, I'm really only trying to
understand the performance and lure of the old iron, like vaxes, in
relation to newer iron that I have or can use, and also understand better.
Call it "Comparative Computer Anatomy" if you will...
Perhaps people do not like my approach, but my aim is true.
To make a machine I'd consider to be in the same
class as the 6000
was when new right now I'd expect to see all of the fastest busses in use
and multiples of them for parallelism.
This is, unfortunatly, gobbdleygook to me. "multiples of them for parallelism"?
Why would this be necessary? Why can't one fast one be used?
Current generation PCs most of us have access to are
not this case and do
perform well below the processor chips capabilities
I don't understand this, either. Are you saying that if there were
memory-speed peripherals, I/O could flow through the processor faster than
existing PC busses? If so, then I definitely agree with you. However,
then bus design gets complicated with cache-coherency etc. I think this
is why you want at least two busses on a machine: memory and I/O. (As
network speeds increase beyond 1 Gb/s, then perhaps a special Network Bus
will be required, too.)
despite AGI, PCI,
SCSI++ (LVUW), copper giga and fibre. Because even the simplest process
like routing a packet requires the cpu to look at the address and see if
it belongs to the port A or port B list and all the DMA in the world
doenst get around that.
right! That's what I was arging before concerning "processing".
A good example is the DEC ugly(by some) RQDX MSCP disk
controller.
While Qbus is maxed out around 4m words a second this controller can do
one thing to keep the lowly vax off it. It can DO DMA from LINKED lists
so that the controller is doing queued IOs. Now thats low end 1987
MicrovaxII technology but if we scaled that and put it on the PC it could
be keeping the cache filled and other tasks while all the cpu has to do is
set up task lists for it.
Sounds like what we now call "scatter/gather DMA" - and is a great idea
for networking stacks.
Another is this RAID thing, a good idea if you have
SCSI. The VAX
was doing it over 14 years ago as part of the OS (disk shadowing).
This is, as I understand it, not -quite- true. Disk Shadowing (what is
that, RAID-1 ?) is a simple technique, not as sophisticated as RAID-5,
for example.
But I remain unclear how this helps us understand busses?
OK so your 486 can do interger math faster, few said
it was false.
Right, and those that few that disagreed were wrong. ;-)
It's
just not enough of a measure. Less so to those guy where processing is
putting the right data (or part) in the correct bin and charging off
10,223.245 (yes three digits!) each for them. It may be meaningless
to the weather service that runs models that have data matricies that can
fill gigabytes of ram (which has to be filled first!) from their terabyte
disk farms.
Right. But, for my goal of attempting to put these old, "obsolete", err, I
mean "ancient", err, I guess it's PC (Politically Correct!) to say
"Classic"
machines in perspective.
All those MIPS, MFLOP and Dhrystones are wasted if the
system structure
is hung up waiting for the floppy.
You mean if the system is waiting for some I/O device? Sure!
If your are preaching newer is faster, the choir is
over there, they know
the words.
I'm not. (But it -is- a fact, though. "Obsolete Ready" as they say...)
If your saying PCs are better, well, put some bounds
around
that as I really feel it's one of those ALWAYS/NEVER generalizations
that often bite.
For the nth time: a dx2/66 is 2 to 3x as fast as a uniprocessor 6500 on
Dhrystone 2.1; this is what I've maintained, and it helps put at least
part of the history of vaxes in perspective for me.
I think we are all fully aware that there are other aspects that need to
be considered to put the vax history in total perspective.
-Mike C
p.s. Allison, just curious, are you a recovering DECaholic? ;-) Your ferver
for the old DEC stuff is amazing to me! Religion? It's fun to watch!