Early IBM machines and parts

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Re: Early IBM machines and parts

Postby TheRevva on Sat Jul 21, 2012 11:07 am

Thanx for the welcome people...
OK, I'll see what I can do about throwing up a post about myself in the intro area. Truly though, I am NOT that interesting... Just a little eccentric perhaps... <Grins>
I'll keep my eyes open for that AT case & PSU for ya, but don't hold your breath. They've become fairly scarce.
As for the production machine, I doubt it really warrants a separate new thread, but I'm sure Terry can 'migrate' this post if he thinks it's relevant enough.
Since I'm not the 'owner' of these two 'production' machines, I have to be a little 'vague' so that I avoid any embarrassment due to the fact that they still need to run 1980's technology.
Here's a quick and dirty description:
The two machines are Pentium-1 (133MHz IIRC) each with 64MB of SIMM and a 130MB IDE HDD. (They're both from Dell... Optiplex I think). There's a VGA chipset on the motherboard as an onboard PCI based VGA.
They each have a couple of highly proprietary ISA cards in them (built using wire-wrap technology). This is one of the primary reasons that they need to run on 'State-Of-The-Ark' iron.
(There's also a couple of empty PCI slots on the motherboard).
The O/S used on them is CDOS (Concurrent DOS) which I recall was the successor to CCPM86.
In their original form, they also have an LPT + MDA combo card in them, and this is where my 'issue' sprang from.
The onboard VGA is used primarily as an independent output screen. Text only using VGA mode 03H (80x25 colour). The application suite appears to write directly to the VGA RAM at B800:0000.
The add in MDA+LPT card is the primary head and is used as the primary system input. (OK, there's also an ancient Wyse-60 dumb terminal attached to a serial port, but that's of lesser importance)
Sooooo, I can almost hear people asking: "What the heck is the 8-bit VGA for?"
Well, we ALL know that it's getting a little difficult to find an MDA capable monitor and those old CRTs take up a decent amount of desk-real-estate.
Furthermore, the 'quality' of the text that's output to an MDA monitor is... Well... It's very '1980-ish' (I hope that's suitably subtle?)

The last of the MDA monitors was about to die (the LOPT was beginning to do STRANGE things, no doubt due to the fact that about half of the electrolytics in the thing were oozing out all manner of foul gunk).
I guess I COULD have given that monitor a birthday, but I wanted something 'better'.
To start with, I began looking for a suitable replacement MDA monitor and came to the conclusion that I couldn't just go out and buy a NEW one anymore. <Sigh>
My next step was to give serious consideration to grabbing a small LCD Television and 'butchering' it into accepting the TTL MDA input. (The MDA line frequency was 'in the ballpark' to within a few kHz).
Amazingly enough, that actually WORKED on the second attempt, but it still just LOOKED ugly so it got ditched in favour of the the almost dead MDA screen.
My next thought was to try a scan doubler so that I could use an easily available current technology LCD VGA monitor.
I did find one that worked (I cannot remember the make / model), but it was still UGLY.
About that time, a small lightbulb in my vintage cranium started flashing.
Any VGA card can 'emulate' an MDA card (by using video more 07). In doing so, the video RAM is 'switched' to be at B000:0000 and the CRTC is switched from 03D4/5 to 03B4/5.
The OUTPUT of the VGA when in mode 07 is still at a VGA line frequency though (31 or so kHz) meaning that a nice VGA LCD can be used.
I tried all manner of PCI VGA cards, but I simply could not get it to work. (Due to constraints of the proprietary software, I could not just throw the PCI card into a text-based framebuffer mode. The video RAM HAD to 'exist' at the usual B000 or B800 segment). I'm fairly certain that the MoBo BIOS itself had setup the PCI bridge to exclude one or other VGA as BOTH appeared to be PCI cards)
I just happened to have an old 8-bit trident ISA VGA card so I threw that in.
The 'problem' was that the MoBo BIOS would either allow the MoBo VGA _OR_ the add-in VGA, but not BOTH at once.
After a little 'head-scratching'. I came to the conclusion that I could 'FOOL' the BIOS on the MoBo into believing the add-in card simply wasn't present. (I yanked out the BIOS from the add-in card).
Sure enough, the MoBo BIOS stopped believing in the existence of the add in VGA card.
However, BOTH of the VGA subsystems were still 'listening' (and responding) to I/O at the normal VGA ports (Eg: 03Bx thru 03Dx).
Whenever I tried to setup ONE card, BOTH cards would get setup... NOT exactly what I wanted, but a lot closer!!!
(Furthermore, this whole exercise was somewhat risky to say the least. Technically speaking, TWO devices were simultaneously replying to I/O and VGA memory accesses. I had to assume the PCI to ISA bridge was somehow arbitrating?)
After a LOT of 'digging', I found that I could place ONE of the VGA subsystems 'to sleep' using I/O port 46E8 such that it stopped listening to all of the normal VGA I/O and memory R/W activity. (I cannot recall which one).
Initially BOTH VGAs are 'awake' and BOTH get setup into VGA text mode 03.
I put ONE VGA 'to sleep' using I/O 46E8
Then I switch over the VGA that's still 'awake' to mode 07 (MDA emulation mode)
I then 'wake up' the sleeping card (which is still in VGA mode 03.
It's a HUGE kludge (from a software perspective), but amazingly, it works!
Posts: 4
Joined: Thu Jul 19, 2012 12:42 pm

Re: Early IBM machines and parts

Postby RdM on Tue Aug 14, 2012 12:50 am

RdM wrote:Sorry to take so long to reply!

- MFM hard drives and controllers

Apart from a jet engine-sounding Rodime brick, marked intermittent sector not found, no MFM drives left; sadly ISTRC also throwing out old Kalok octagon & early IBM? RLL drives much earlier.
That Rodime maybe 5MB is likely not really useable except as an artifact.
But I do have some few MFM/RLL controller XT boards, I think.

- any IDE hard drive below 500Mb - smaller the better

Ah, now, (after all this time, checking them out ;-) - quite a choice!]
[Listed without prejudice, or intent to treat; - just a list, so far! ;=})]
[and I'm considering testing them, what it takes, & so forth ... ;-) ]
2x Seagate ST351A/X 40MB (stepper motor)
(jumpers for XT/AT operation)
http://support.dell.com/support/edocs/d ... 000003.htm

1x Seagate ST3144A 130MB

1x Miniscribe 8051A 40MB

1x Quantum ProDrive LPS 52AT 50MB

1x Quantum ProDrive ELS 127AT 120MB

1x Quantum ProDrive ELS 210AT 210MB

1x Quantum ProDrive ELS 420AT 420MB

1x Conner CP30104H 120MB

1x Conner CP30201 212MB

2x Conner CP30254 250MB

1x Conner CFS850A 850MB

1x Fujitsu M2681TAM 264MB ATA2 Fast (256kb cache)

1x Maxtor 7120AT 120MB

1x Maxtor 7540AV 540MB

1x Western Digital Caviar 140 42.6GB

3x Western Digital Caviar 1210 212MB (128kb cache) (one noisy)
(other two have Win95 installs from note) (need to check what else)


- Normal CGA or EGA display

Sad to report I tossed a CGA a few years ago; I still have some EGA boards, not sure on CGA

- Monochrome 9 pin display (I have one working now, but it gets shared)

Ah well, now here's where it gets more interesting...

You might like this perfectly functioning item I spray-painted satin black from beige years ago, all dismantled to do so & even a green metallic spot for the on-off knob, & years later stored since seems still fine ... an Intra brand mono monitor:



front - off.jpg

lower front CU-sm.jpg


Anyway, I'll see about testing some or all of the hard drives - let me know what you might be interested in.

The Intra monitor I had stuck on TM last year, to no interest - I'd be happy to see it go to a good home for a modest amount - what offer?


I've re-listed the monitor on TM - had thought lost for a while; - & since Jono found IBM's since, is up for grabs!

http://www.trademe.co.nz/Browse/Listing ... =503467052

Negotiation possible.

Meanwhile, if any wanted interest in the above HD details, please let me know!
Posts: 27
Joined: Thu Mar 24, 2011 7:13 pm


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