[cctalk] Re: SCAMP at 61 (IBM Scientific Computer And Modular Processor) was Re: SCAMP at 50 (IBM 5100)

[Tom Stepleton via cctalk]

I have to assume that the SCAMP used in the IBM 5100 Portable Computer and
relatives must have been a great deal smaller than the earlier machine.

As such, a logical and unambiguous way to refer to it is "SCAMP Shrimpy."

I hope this is helpful,
--Tom

[cctalk] Recovering floppies attacked by mould

[Tom Stepleton via cctalk]

Greetings,

Amidst all the floppy archiving discussion, here's a slightly different
question:

The weather is warmer now where I live, so it's starting to be a good time
to do messy work outdoors. I have some mouldy floppy diskettes that I'd
like to try to read (mostly 5.25"), plus a good flux reader. What is the
best way to attempt to image these floppies?

My thinking right now is that for each floppy I can attempt this procedure:
- remove the mouldy cookie from the infected disk jacket; discard the latter
- give the cookie the best clean I can (how?) and allow to dry
- place the cookie in a clean disk jacket
- attempt to image
- clean floppy drive heads

Does this seem like a sensible plan? If so, what would be the best way to
clean as much mould off the cookie as I can? Tools that come to mind are
distilled water (tap water here is full of chalk), dish soap,
cyclomethicone, and of course more fearsome solvents. I have kimwipes,
microfibre cloths, and... 200-grit sandpaper, I guess :-)

Thanks for any advice,
--Tom

[cctalk] Re: Whitechapel Computer Works

[Tom Stepleton via cctalk]

I forgot to add that some gradual but real progress on adding the MG-1 to
MAME is taking place as well. --Tom

On Sat, Nov 5, 2022 at 7:01 PM Tom Stepleton  wrote:

> On Fri, 4 Nov 2022 17:53:10 PM Tony Duell  wrote:
>
>> More seriously I have a working (last time I turned it on) MG1 with
>> monitor, keyboard, and mouse. Also have the technical notes manual and
>> an installation disk kit. Another chap I know (I think he's here but
>> I'll let him speak up) scanned the manual and coppied the disks last
>> year, so there is a backup.This is a 32016-based machine of course. It
>>
>
> Yes hello, this is me. In fact, if you would like to see the Whitechapel
> MG-1 in my possession in operation, come up tomorrow (Sunday) to the Centre
> for Computing History in Cambridge, where the system is on public display
> alongside an AT with a busy bunch of Transputers in it. It's all part of
> the Retro Computing Festival that's underway this weekend:
>
> http://www.computinghistory.org.uk/det/69485/Retro-Computer-Festival-2022-Saturday-5th-November/
>
> If you can't make it to Cambridge, then when the machine is running (which
> it isn't at the moment --- wait for between 10 AM and 5 PM GMT Sunday), you
> can visit the machine over HTTP at http://mg-1.uk . (Note no https.)
>
> Working MG-1s and related machines (like the colour CG-1) are rare owing
> to leaky batteries (what else).
>
> I'm very grateful to Tony for his generous sharing of MG-1 materials ---
> it helps make it possible to show off the MG-1 in this way! I've got
> everything on Google Drive, with links available on the website just
> mentioned. Since it's liable to be down when you're reading this, here's an
> archive.org link:
>
> https://web.archive.org/web/20210625124716/http://mg-1.uk/
>
> Note also this page with links to 42nix 2.6 OS media, also owing to Tony:
>
> https://web.archive.org/web/20210625124758/http://mg-1.uk/42nix/42nix.html
>
> You will probably have to edit archive.org's links out to Google Drive in
> order for them to work, but I think it should be pretty easy to do this.
>
> I have been meaning to make disk images of my best-effort reconstruction
> of a clean 42nix 2.5 installation (a predecessor to the version linked
> above), which I derived from a disk image taken from one of Jim Austin's
> MG-1s. There is not a vast difference for the user at the console between
> 2.5 and 2.6, although they did fix a bug in the TCP/IP implementation that
> allows a forking HTTP server running on 2.5 to cause a kernel panic. I
> suspect revisions to TCP/IP were required to get NFS working, which, I
> remember concluding, had been a new feature for 2.6.
>
> I've never been able to get my hands on GENIX.
>
> All sorts of spare boards, including things like never-populated bare
>> RAM boards for the Hitech,.
>>
>
> It took me a lot longer than I like to admit to realise that HITECH was
> derived from wHITECHapel...
>
> Speaking of discoveries, I found out today that the Centre for Computing
> History is in possession of a couple Hitech MIPS machines (sans cases).
> Apparently they might have some media on QIC tapes as well. Tony, I'll try
> to get you in touch with the person I was speaking with about this.
>
> Meanwhile TNMOC at Bletchley are in possession of three MG-1s.
>
> --Tom
>

[cctalk] Re: Whitechapel Computer Works

[Tom Stepleton via cctalk]

On Fri, 4 Nov 2022 17:53:10 PM Tony Duell  wrote:

> More seriously I have a working (last time I turned it on) MG1 with
> monitor, keyboard, and mouse. Also have the technical notes manual and
> an installation disk kit. Another chap I know (I think he's here but
> I'll let him speak up) scanned the manual and coppied the disks last
> year, so there is a backup.This is a 32016-based machine of course. It
>

Yes hello, this is me. In fact, if you would like to see the Whitechapel
MG-1 in my possession in operation, come up tomorrow (Sunday) to the Centre
for Computing History in Cambridge, where the system is on public display
alongside an AT with a busy bunch of Transputers in it. It's all part of
the Retro Computing Festival that's underway this weekend:
http://www.computinghistory.org.uk/det/69485/Retro-Computer-Festival-2022-Saturday-5th-November/

If you can't make it to Cambridge, then when the machine is running (which
it isn't at the moment --- wait for between 10 AM and 5 PM GMT Sunday), you
can visit the machine over HTTP at http://mg-1.uk . (Note no https.)

Working MG-1s and related machines (like the colour CG-1) are rare owing to
leaky batteries (what else).

I'm very grateful to Tony for his generous sharing of MG-1 materials --- it
helps make it possible to show off the MG-1 in this way! I've got
everything on Google Drive, with links available on the website just
mentioned. Since it's liable to be down when you're reading this, here's an
archive.org link:

https://web.archive.org/web/20210625124716/http://mg-1.uk/

Note also this page with links to 42nix 2.6 OS media, also owing to Tony:

https://web.archive.org/web/20210625124758/http://mg-1.uk/42nix/42nix.html

You will probably have to edit archive.org's links out to Google Drive in
order for them to work, but I think it should be pretty easy to do this.

I have been meaning to make disk images of my best-effort reconstruction of
a clean 42nix 2.5 installation (a predecessor to the version linked above),
which I derived from a disk image taken from one of Jim Austin's MG-1s.
There is not a vast difference for the user at the console between 2.5 and
2.6, although they did fix a bug in the TCP/IP implementation that allows a
forking HTTP server running on 2.5 to cause a kernel panic. I suspect
revisions to TCP/IP were required to get NFS working, which, I remember
concluding, had been a new feature for 2.6.

I've never been able to get my hands on GENIX.

All sorts of spare boards, including things like never-populated bare
> RAM boards for the Hitech,.
>

It took me a lot longer than I like to admit to realise that HITECH was
derived from wHITECHapel...

Speaking of discoveries, I found out today that the Centre for Computing
History is in possession of a couple Hitech MIPS machines (sans cases).
Apparently they might have some media on QIC tapes as well. Tony, I'll try
to get you in touch with the person I was speaking with about this.

Meanwhile TNMOC at Bletchley are in possession of three MG-1s.

--Tom

[cctalk] Re: You have Apple Lisa 1 "twiggy" system to trade for my IBM 5100 Portable PC?

[Tom Stepleton via cctalk]

> >> Are you sure about that? The 5100 doesn't support floppy drives. And
> I've
> >> never heard of third-party drives (that would need IMFs, too) for the
> 5100.
> >
> > $3100 is about what IBM charged for a fully loaded 5150. (PC)
> > THAT is not a 5100!   $3100 for a 5100 would have been a bargain.
>
> We are neither talking about the 5150, nor about $3100 but $31,000 for a
> 5100 (see above). Or did I miss something?
>

There was a third-party floppy drive for the IBM 5100 :-)

Or at least there as something that was sold in this way. Here is its
brochure:

http://www.bitsavers.org/pdf/sykes/brochures/Sykes_Comm-Stor_5100_Brochure.pdf

Note that it "plugs directly into the Serial I/O Adapter of the IBM 5100
with no hardware or software changes". So it's a serial-port connected
floppy drive that talks to the 5100 in a format that it likes.

(What is an IMF?)

--Tom

"Voltmitten": an amateur overdesigns a DC voltage monitor

[Tom Stepleton via cctalk]

Hi cctalk,

Ever since CuriousMarc put out his YouTube horror film last April
about a killer
HP 9825T power supply
,
I've been worrying about how my own comparably-aged systems might avoid a
similar fate, at least until I have the wherewithal to do a Jerry Walker
-esque
high-quality PSU refurbishment.

In the end, borrowing a tactic from Commodore fans, I made a circuit that
sits between a DC power supply and a load and cuts off the power if it
senses an overvoltage or an undervoltage condition. I'm happy to share it
with you now, with the usual anxiety amateurs feel when an audience
includes some professionals. I hope at least some elements of the design
can be useful! Here it is: https://github.com/stepleton/voltmitten/

(There are two reasons for the name "Voltmitten". One is that the gizmo is
shaped a bit like a hand. The other is to remind you that it wasn't really
designed by the most serious practitioner.)

You can see my cute mock video advert for Voltmitten here:
https://youtu.be/hSaAHBhTh_A
I hope it's an adequate homage to Marc's inspiring videos. Most of the
effort here went into a brief gag view of a carefully rotoscoped
 Bob Stern aka
"Mr. Fancy Pants", which may not have been the best use of time but is at
least a result I can feel proud of :-)

With best wishes for a bright 2022,
--Tom

Power supply power-up and power-down sequencing: how did it work?

[Tom Stepleton via cctalk]

Hi cctalk,

I asked this question over on vcfed, but in the spirit of knowing more (and
avoiding silly, costly mistakes) I thought I'd ask again here. I hope this
is okay --- I think there must be a lot of community expertise to draw
from, and not everyone is in the same forums.

After seeing CuriousMarc's horror film about the killer transistor that
zapped the guts of his HP9825T, I've been working for some time on a
solid-state DC power supply monitor device that will chop all power to
logic if there's ever any excursion above or below critical voltage
thresholds on any power supply channel. I've been pretty successful in the
development so far and have a gizmo that accomplishes the basic goal, even
if it's not going to win any industrial design awards. It's not a crowbar
circuit: each voltage channel passes through a substantial driver IC that
can switch the power right off.

My device can detect and react to anomalies very quickly. But then you
browse through old DRAM datasheets and see warnings like these:

"Vbb must be applied prior to Vcc and Vdd. Vbb must also be the last power
supply switched off."

"Forward biasing this supply [that is, Vbb] with respect to Vss will
destroy the memory device."

And so even though my device is fast, it's possible that when it's slamming
the doors shut, there's a split second where -5V is off and +12V is still
on, or even the chance of a Vbb-Vss forward-bias "blip", who knows? Of
course you can measure whether this is happening, but it's difficult to
know how meaningful that will be: maybe a computer that loads the voltage
rails differently will have different behaviour, and remember, the case you
really care about is when a power supply behaves abnormally! System
characterisation is hard...

Anyway, my question is: what did hardware designers in the '70s do to
satisfy specified power supply requirements for the chips they were using?

The conversation so far on vcfed has two remarks: one observing that a lot
of folks just didn't worry about it, and one pointing out an anti Vbb>Vss
gimmick in the PSU for the Nascom kit computer involving a ladder of
protective diodes between each of the rails:

(-12V) >| (-5V) >| (0V) >| (+5V) >| (+12V)

I noticed a similar pattern in a few other PSU schematics, but usually only
for the negative channels.

Were there any other common tricks? How serious was the danger of getting
it wrong? How fast could you fry your DRAM if you did?

Thanks for any insight,
--Tom

Re: Extremely CISC instructions

[Tom Stepleton via cctalk]

Thanks for the suggestions, all --- more than I was expecting! I have
plenty of reading waiting for me now, but I hope people won't let that stop
them from sharing other examples.

Cheers,
--Tom

On Wed, Aug 25, 2021 at 6:08 PM Josh Dersch  wrote:

> On Mon, Aug 23, 2021 at 5:38 PM Tom Stepleton via cctalk <
> cctalk@classiccmp.org> wrote:
>
>> Hello,
>>
>> For the sake of illustration to folks who are not necessarily used to
>> thinking about what computers do at the machine code level, I'm interested
>> in collecting examples of single instructions for any CPU architecture
>> that
>> are unusually prolific in one way or another. This request is highly
>> underconstrained, so I have to rely on peoples' good taste to determine
>> what counts as "interesting" here.
>>
>
> I'll submit the Xerox Alto, with its extensions to the base DG Nova
> instruction set.  It included "CONVERT", used to render font glyphs to the
> screen, and of course the legendary "BITBLT" for transferring bitmaps
> across arbitrary bit boundaries.  Both of these were complicated
> operationst, and the latter revolutionized computer graphics...
>
> See p. 18 and 22 of
> http://bitsavers.org/pdf/xerox/alto/AltoHWRef.part1.pdf.
>
> (The Three Rivers PERQ included a similar "RASTEROP" instruction in its
> repertoire, which was similar to BITBLT but also allowed for various
> logical operations to be applied to the source and destination.)
>
> - Josh
>
>
>

Extremely CISC instructions

[Tom Stepleton via cctalk]

Hello,

For the sake of illustration to folks who are not necessarily used to
thinking about what computers do at the machine code level, I'm interested
in collecting examples of single instructions for any CPU architecture that
are unusually prolific in one way or another. This request is highly
underconstrained, so I have to rely on peoples' good taste to determine
what counts as "interesting" here. Perhaps a whole lot of different kinds
of work or lots of different resources accessed is what I'm after. I expect
these kinds of "busy" instructions were more common in architectures that
are now less common, so perhaps this list is a good place to ask.

For example, if we're thinking "number of times an item is retrieved from
RAM", then any application of the x86 string instructions that could walk
over memory for a while perhaps aren't so interesting. By contrast, by my
count, the NS32000 series instruction "addw ext(4), ext(7)" requires at
least five separate noncontiguous retrievals just to fetch the arguments
into the ALU. (Note that I'm not differentiating between different sizes of
data here: loading a 16-bit item and loading a 32-bit address both count as
a "retrieval" in this example.)

Instructions that are simply lengthy might be interesting, but not always:
long literals or lots of redundant prefixes on x86 aren't that impressive,
for example.

Number of registers read or modified might be good too, but just saving or
loading for the sake of subroutine calls (e.g. "movem.l r0-r7/a0-a6,-(sp)"
on the 68k) seems pretty pedestrian.

Other criteria may seem worthwhile; I trust peoples' judgement on this.
Although I don't know it well, I suspect VAX will place well in one way or
another. But to give an example of a candidate instruction that's prolific
in a way I find more noteworthy, I'll go back to the NS32k and offer

  addw ext(4)+6[r1:w], ext(7)+12[r2:w]

which in order to get its arguments (I think) requires the five retrievals
already mentioned and adds two shifts and four additions to the bill. I
think this statement reads: "Add the r1'th word counting from 6 bytes past
the fourth address in the current module's link table to the r2'th word
counting from 12 bytes past the seventh address in the current module's
link table". That's a mouthful --- it takes a lot of work to describe what
that one line does! Maybe that's what I'm hoping to share with people.

I hope this is interesting to discuss,
--Tom

Re: Replicating IBM SLT/MST card interconnect

[Tom Stepleton via cctalk]

There wasn't much advice to be had on making modern connectors that
interoperate with the header-like connectors used by IBM SLT cards, so I
did my best to come up with some on my own. This design appears to be
functional, but I've only ohmed it out so far, not put it to any kind of
extended use:

https://github.com/stepleton/SLT_interconnect

The hard part now will be getting my hands on 18 AWG flat ribbon cable that
doesn't cost a fortune.

Anyhow, I hope this might be of use to some folks out there.
--Tom

On Thu, Jul 29, 2021 at 1:21 PM Tom Stepleton  wrote:

> Hi cctalk,
>
> I'm looking to replicate the 24-contact connector system that IBM used on
> SLT and MST cards for many years. Has anyone done this before?
>
> The best photos of this connector that I can find online are on this page:
>
> http://techandtrouble.blogspot.com/2014/04/happy-50th-system360-pt5-anatomy-of-slt.html
> I haven't searched Bitsavers documentation extensively for IBM
> specifications, but I've seen some details around page 54 of this document:
>
> http://www.bitsavers.org/pdf/ibm/logic/SY22-2798-2_LogicBlocks_AutomatedLogicDiagrams_SLT,SLD,ASLT,MST_TO_Oct71.pdf
>
> I'm interested in reproducing both polarities of this connector: plug and
> socket. Also, even though the most familiar use of this connector is for
> board-to-board interconnect, I'm most interested in wire-to-board
> interconnect. IBM used this method for DC power connectors in its  5100,
> 5110, and 5120 computers. Here are images of this specific connector:
> http://stepleton.com/connector/
> taken as still images from a YouTube video on the IBM 5120 by Jerry Walker
> (https://www.youtube.com/c/JerryWalker-JMPrecision/videos).
>
> I've designed and built a device that monitors DC power supply voltages
> for overvoltage and undervoltage excursions and cuts off all power rails if
> any voltage goes out of spec. I hope to use it to protect my own IBM 5100
> from major power supply faults like the one CuriousMarc encountered with
> his 9825T:
> https://www.youtube.com/watch?v=b-eN93L6yX8
>
> In order to put my device between my 5100's power supply and the logic
> card backplane, I need to recreate a plug and a socket so that I can
> fashion a cable that goes out to my device. If anyone has created
> dependable modern versions of these connectors, would you mind sharing any
> pointers?
>
> Thanks for any help,
> --Tom
>

Replicating IBM SLT/MST card interconnect

[Tom Stepleton via cctalk]

Hi cctalk,

I'm looking to replicate the 24-contact connector system that IBM used on
SLT and MST cards for many years. Has anyone done this before?

The best photos of this connector that I can find online are on this page:
http://techandtrouble.blogspot.com/2014/04/happy-50th-system360-pt5-anatomy-of-slt.html
I haven't searched Bitsavers documentation extensively for IBM
specifications, but I've seen some details around page 54 of this document:
http://www.bitsavers.org/pdf/ibm/logic/SY22-2798-2_LogicBlocks_AutomatedLogicDiagrams_SLT,SLD,ASLT,MST_TO_Oct71.pdf

I'm interested in reproducing both polarities of this connector: plug and
socket. Also, even though the most familiar use of this connector is for
board-to-board interconnect, I'm most interested in wire-to-board
interconnect. IBM used this method for DC power connectors in its  5100,
5110, and 5120 computers. Here are images of this specific connector:
http://stepleton.com/connector/
taken as still images from a YouTube video on the IBM 5120 by Jerry Walker (
https://www.youtube.com/c/JerryWalker-JMPrecision/videos).

I've designed and built a device that monitors DC power supply voltages for
overvoltage and undervoltage excursions and cuts off all power rails if any
voltage goes out of spec. I hope to use it to protect my own IBM 5100 from
major power supply faults like the one CuriousMarc encountered with his
9825T:
https://www.youtube.com/watch?v=b-eN93L6yX8

In order to put my device between my 5100's power supply and the logic card
backplane, I need to recreate a plug and a socket so that I can fashion a
cable that goes out to my device. If anyone has created dependable modern
versions of these connectors, would you mind sharing any pointers?

Thanks for any help,
--Tom