Saturday, July 16, 2011

Detour #2 - The PC/XT Clone

One of the best times of my career was working with IBM PC/XT systems. Like many things we retro nerds play with, it seems quite primitive by today's standards. But this machine really did usher in the age where business got done with personal computers. And I had the good fortune to be right in the middle of it.

At Hughes Aircraft in the mid 80s, we were pretty much standardized on true-blue IBM. There was a small installed base of Compaq systems, and eventually clones got good enough to rely upon. While the clone dealer we worked with made very good systems, nothing really ever beat the tank-like quality of PC/XTs. I'm not convinced anything short of mil-spec equipment ever will. They were very nearly indestructible, and I can attest to this firsthand.

For this reason, using my PC Portable 5155 has been a joy. It's basically a PC/XT in a portable case, with 9" amber screen, dual 5.25" 360K floppy drives and CGA video in a very well-built case. The 5155 does have some inherent limitations, though - most notably, room for expansion. The form factor of the case makes it difficult to upgrade, since much of the card slot area is blocked by other components. Many of the card slots will only accept half-length cards, and 2 of the 3 full length slots are blocked by the built-in cards (CGA, floppy controller). I was able to get an AST SixPak Plus in there, luckily - otherwise I would have been stuck at a listless 256K of RAM.

Years ago, a buddy of mine gave me a turbo XT clone that he had used back in the day. To the best of his knowledge it was working, but it was missing parts. I had thought a couple of times of robbing parts from the PC 5155, since the clone case would be much more expandable, and more like the desktop machines I used back in the day. But I couldn't bring myself to gut a perfectly working piece of history.

Until it died.

I have a pretty pragmatic approach to my vintage computing. I don't buy something unless it works - no museum pieces. I also don't buy anything so expensive that I'm hesitant to play with it. So when it dies, I either repair it, or give it away. This time was weird and different, since I decided to harvest parts. But it was clear from troubleshooting that something on the motherboard was amiss, so I knew I could get working boards, etc.

It was a challenge to extract the keyboard. The keyboard just snaps off the unit, but the connector is an RJ-style hookup. Inside the 5155, the cable is translated to a standard 5-pin DIN cable by an adapter. I had to extract that adapter, which required some careful disassembly.

Here is the keyboard cable and attached adapter (extracted from within the 5155):

Here is the clone box open:

Card from left to right: CGA video adapter (from 5155), AST SixPak Plus (recovered from 5155), Western Digital FileCard hard drive on a card (10 MB), D-Link 10 Mbps ISA Ethernet card (yes, it networks!), and floppy controller (from the 5155). That's a single 5.25" 360K floppy on the right.

This case and power supply has a very PC/XT reminiscent feel. However, it is clone hardware, lacking a bit of the fit and finish of a real XT. It is pretty nice, though.

I connected it all and fired it up - success!

I did have to install DOS and other related software onto the hard card - more on all that later.

Here's a close-up shot of the computer with DOS running, showing the memory usage:

(Sorry that last pic is a bit dark - the screen doesn't show up well with a flash.)

That's all for now - I need to get started on my real Retrochallenge project! More later on the hard card, networking with Novell Netware 3.12, etc...

1 comment:

Stew said...

It wasn't too long ago that the future of aircraft hardware relied heavily on IBM computers. Now its the battle for the best software that will work "out there" in forms of apps, tools, and systems. Gone are the days of those XT series.