< I expect this was almost essential; all of the wiring between circuit
< cards was on the inside of the circle, and the customer engineers had to
< able to get to that wiring.
True.
< I suspect that the reason Seymour Cray built the machine in the shape h
< did was that the circuit cards, plus the machined columns that supporte
< and cooled them, were wider than the card connectors. By arranging the
< card columns in a semi-circle with the connectors on the inside, he coul
< minimize wiring length.
It was a design requirement that no signal path would exceed 1 meter.
It also allowed signals like clock to be distributed in a way that
assured all parts were geting the same drumbeat at the same time. If it
were a linear layout it would easily be several meters long and the
signals from either end would have cables long enough to insure the
data was way late.
Signal propagation in cables is less than speed of light (c) and can be
as low as 75% in some coax style cables. So if you have a 3 meter cable
and you putting pulses out at the rate of one every 3nS you can literally
have three pulses traveling down the wire like golf balls in a tube! If
that pulse is your sychronizing clock you can see that when it gets to
the end of that 3meter wire it's late (by two pulses) compared to the
logic at the beginning of the wire. This is a handicap for ultrafast
systems but it can be useful for storing data too (delay line memories
and timing elements)! So this is why big and fast do not go well
together.
It also was an advantageous layout for cooling and power distribution.
It made for an unusual looking machine with a lot going on down under
the subfloor! Customer engineers were not that fond of it as it tended
to be cold in the middle!
This phenomenon is seen and known at the chip level and influences
how the logic is organized on the die for super fast logic.
Allison
< For all you DEC people, this sounds like an interesting book. The
< description is "Microcomputers and Memories" (1981, DEC, 662 Pages,
< Softbound).
<
< http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=35707674
It's a must have for anyone hacking Qbus PDP-11s, peripherals commonly
used with PDP-11s and even user designed hardware! I have the 1982
version and it's well used!
Allison
I should include the more regional measure:
NewYork Second:
That is the infinitesmal time between the light turning green and the cab
horn going off behind you.
Allison
>Motorola claims to have started shipping ECL integrated circuits in 1962.
>Why were people still building computers using discrete transistors for
>years after that? Many of the high-end computers used discrete
>implementations of non-saturating logic that was very similar to ECL.
Most of the early IC production went into defense electronics, especially
missile guidance computers. Even after IC's were commercially available,
they were quite expensive, even in production quantities.
IBM continued to ship new SLT-based designs when their competitors were
moving to IC's, and they were the target of some marketing hype as a
result. However, IBM had tuned the circuit design, packaging and
manufacturing processes for SLT so well that they could get more
performance per dollar out of SLT than anyone could get out of IC's.
(Source: Pugh, Johnson and Palmer, "IBM's 360 and Early 370 Systems", MIT
Press.)
----
John Dykstra jdykstra(a)nortel.com
Principal Software Architect voice: +1 651 415-1604
Nortel (Northern Telecom) fax: +1 612 932-8549
< >As this forum is based upon Classic Computers I have a
< >theoretical question for you all.
< >Which do you prefer, the original system or an emulation?
Emulators have their place where hardware is scarce or extinct.
What you can't do with an emulator is make the disk drive buzz out a
tune or hack the DMA logic as a simple blitter. Hardware has aspects,
some very tactile, that emulators can't. Also if the emulator doesn't
know the proposed hardware it can't. I'd love to see an emulator that
could imitate a s100 z80 system!
I do use an emulator, MYZ80. However I find that I end up copying the
work to my s100 crate, ampro, visual or kaypro in the end.
Allison
> As this forum is based upon Classic Computers I have a
> theoretical question for you all.
> Which do you prefer, the original system or an emulation?
An emulation can never produce the genuine beep of an
Apple ][ at power on, never, no, not now and not when
using 128Bit 32 chanal thousend times oversampling :)
Just the beep - and now go for all the other fun things.
Gruss
H.
P.S.: Did I mention the ratatatak when retracting the
Disk ][ heads ?
--
Ich denke, also bin ich, also gut
HRK
>>>> Oh well. It would have been an interesting idea.
> well I'd be interested, but the big problem's transport at the moment.
> Give me a couple of months and then ask again :)
Transport ?
Rent a car, open the door, put in the computers,
as a friend to push you in and close the door and
drive - or do you want to display a 1:1 Univac
rebuild ?
>>>> Yeah, and given the geographic spread of the people that did reply, even
>>>> a pub meet would be out of the question.
>>> Jep, just for 3 hours would be a bit short - I'll think
>>> you have to change your horrible pub opening hours.
> well rumour has it that they might be changing. At the moment all you
> need to do is find a good pub with a decent landlord who isn't bothered
> about closing at the official times. It's not difficult!
So, are we about do get a micro-VCF (only SBCs
are alowed) in GB within the next few month ?
I'm in for shure.
Gruss
H.
--
Ich denke, also bin ich, also gut
HRK
> My pet peve is the IBM PC when launched was clocked at a rather poor
> 4.77mhz when most of the s100, multibus and generally everyone else
> that went with 16bits were looking for 8mhz or faster if possible.
> It saved a few dollars but not enough. At least DEC had a z80 in
> there to also do IO (instead of the IOC).
Jep, Even the Z80 was at 6MHz at this time - But to be
honest we have to agree that the basic design of the PC
was just intended ans a more flexible terminal, and this
basic design was enhanced for the PC...
>< P.S.: The hate-segmentation-rantig against the x86 also drives
>< me mad - the segmentation sceme used is a very good compromise
>< between usability and performance. Loosing up to 15 Bytes
>< per segment isn't realy a drawback compared to granularities
>< of 4 or 8K today ...
> To me segmentation was just another bag on the side to get 16bits to
> address more.
Jep right, and a very andsome way to deliver relocable adressing
and simple memory management.
> The other half is that MMU granularity makes sense for its time but with
> modern OSs eating megabytes for the kernel Even segments don't allow
> enough.
:))))
Unix and MS ...
H.
--
Ich denke, also bin ich, also gut
HRK
>As this forum is based upon Classic Computers I have a
>theoretical question for you all.
>Which do you prefer, the original system or an emulation?
For me, the real machine is more important. An emulation is a poor
replacement (especially if it has to run under Microsoft-anything).
But with some hardware being in very short quantity, an emulator
can fulfill a need.
I'm in the process of working on a pdp-10 emulator, but that is
not to say that I would turn down real hardware... my only problem
right now is lack of space. I definitely could not handle a KA,
KI or KL... but a KS? Good possibiliy... the disks are another
problem, however.
Megan Gentry
Former RT-11 Developer
+--------------------------------+-------------------------------------+
| Megan Gentry, EMT/B, PP-ASEL | Internet (work): gentry!zk3.dec.com |
| Unix Support Engineering Group | (home): mbg!world.std.com |
| Compaq Computer Corporation | addresses need '@' in place of '!' |
| 110 Spitbrook Rd. ZK03-2/T43 | URL: http://world.std.com/~mbg/ |
| Nashua, NH 03062 | "pdp-11 programmer - some assembler |
| (603) 884 1055 | required." - mbg |
+--------------------------------+-------------------------------------+
BSD derived boxes have the ^T status available... see below from my
Freebsd 2.2.7 box (AMD 586/133)
Script started on Tue Oct 20 08:42:46 1998
#134 i4got:/home/pechter>^T load: 0.22 cmd: ksh 15420 [ttyin] 0.03u 0.06s 0% 472k
Script done on Tue Oct 20 08:42:54 1998
Bill
(wishing for both Tops-20 and Vax/Vms on my pc)
+---------------------------------------------------------------------------+
| Bill and/or Carolyn Pechter | pechter(a)shell.monmouth.com |
| Bill Gates is a Persian cat and a monocle away from being a villain in |
| a James Bond movie -- Dennis Miller |
+---------------------------------------------------------------------------+
