Oldskooler Ramblings

the unlikely child born of the home computer wars

Archive for April 22nd, 2008

Beefing up your AT&T PC 6300

Posted by Trixter on April 22, 2008

No, this is not an extremely well-researched elaborate April Fool’s joke; I’m actually serious this time. In this post, I’m going to illustrate ways you can beef up your AT&T PC 6300, just stopping short of throwing it in the garbage and replacing it with an XT clone.

The AT&T PC 6300 was AT&T’s attempt to get into the personal computer market in 1984. AT&T bought the rights to sell the Olivetti M24 in the USA and made it available as the “PC 6300” in late 1984. It exceeded the IBM PC in just about every way:

  • It used an 8MHz 8086, about 2.2x the speed of the IBM PC’s 4.77MHz 8088
  • An extended graphics mode went as high as 640×400 (which also resulted in sharper text in normal text modes)
  • It had special expansion slots that could be used to turn it into the 6300+, which would run AT&T UNIX, or install expanded memory boards (usually required to run AT&T UNIX :-) although the memory could be used as EMS under DOS)
  • It had a few aesthetic improvements: it was smaller and lighter than the IBM PC, and the floppy drives were whisper-quiet
  • It contained a battery-backed internal clock chip that would remember the time and date even if powered off
  • Like Sun machines, the keyboard had a special mouse port on it, so you could buy a 6300 mouse and attach it to the keyboard. Not only did this save desktop area from cable mess, but the “keyboard mouse” had a wicked cool property: If you had no mouse driver loaded, moving the mouse would automatically press up/down/left/right arrow keys for you! You could use the mouse to navigate any program, regardless of whether or not it supported a mouse.

The problem with the 6300 is that those enhancements required many proprietary changes to the unit; they also didn’t predict how long the computer would be useful into the 1990s. These two factors led to some nasty surprises the longer you owned one:

  • The enhanced video required special monitors, and could not easily be replaced with an EGA or VGA card without extreme hardware preperation. Repairing the special monitors was also quite costly; I remember a $300 charge to repair a blown flyback transformer on mine. That repair took two very long months…
  • To support the mouse attachment, the keyboard had a non-standard 9-pin DIN, so you could only hook up AT&T keyboards to it. (Thankfully, there is a schematic on the web you can use to build an adapter to hook up PC/XT keyboards to it.)
  • The motherboard, in an attempt to save space, has slots on the top side but the components and headers on the bottom side. This was a major pain in the ass if you had to reroute cables through the machine (as I had to do when installing a Central Point Option Board).
  • To properly support the 6300 100%, you were strongly encouraged to use AT&T MS-DOS. Other DOS variants, including IBM’s true blue PC-DOS, wouldn’t support the built-in clock chip and other 6300 features.
  • Tweaking CGA, at Seven Spirits of Ra extremes, did not look right with the higher-resolution text mode.
  • The aforementioned clock chip was worse than not being Y2K-compliant — it wasn’t even Y1992 compliant! AT&T used only 3 bits for the year, starting at 1984, which limits the machine to the years 1984-1991. Trying to set the date to anything past January 1st 1992 has the year locked at 1991.

While the above prompted most owners to punt them past 1992, the PC 6300 remains a very interesting compatible in every sense of the word. I still own mine 23 years later, and for those who would like to restore theirs to prime game-playing condition, I am happy to share my secrets on how to “mod” your AT&T PC 6300:

  • Replace the 8086 CPU with an NEC V30. This will boost the machine to 2.1x the speed of an IBM PC.
  • Try to find the 1.43 BIOS chip upgrade if your machine doesn’t already have it (you can see what BIOS revision you have when booting the machine). The enhanced BIOS chips (there were two in the upgrade package) obviously improved program compatibility, although the major players such as Flight Simulator and Lotus 1-2-3 already ran fine. They’re also required if you want to run Microsoft Word for DOS in high-res WYSIWYG mode (see below), but be careful when you install them: They’re not notched, and putting them in backwards will release the magic smoke in about 3 seconds. Please don’t ask me how I know this.
  • Run programs that support the 6300’s special 640×400 graphics mode so you can feel good about maintaining a proprietary clone and monitor. For example, lots of graphical viewers like CSHOW will display B&W gifs at that resolution (and before GIF we had MacPaint images, and the 6300 had a 640×400 MacPaint viewer). There were also some games that could use 640×400, like The Colony. Also, FRACTINT (fast fractal exploration program) will use the special graphics mode. As previously mentioned, Microsoft Word for DOS 4.0 and later will use 640×400 for on-screen WYSIWYG (ie. you italicize a word and it actually shows up italicized. Look, we had it really rough in the 1980s, ok? Please stop laughing!)
  • If you don’t care about 5.25″ floppy compatibility and have a hard drive, flip the DIP switches on the motherboard to enable 96 TPI mode for the floppy drives. You won’t be able to read 5.25″ regular DSDD 40-track disks any more, but you will be able to format 5.25″ disks to 720K (the drives pack 80 tracks onto a disk in that mode). This is really for personal yucks only, as you will only be able to read such disks on a 1.2MB drive.
  • The speaker in the 6300 sucks; make a cable with alligator clips you can use to clip onto the speaker leads and run it to a set of speakers or a stereo.
  • Install an 8087 math coprocessor and run some of the more crazy fractals on FRACTINT (see above) without waiting overnight.
  • If you’re handy with a dremel and have the hard drive model (one floppy drive and one hard drive), cut a vertical 3.5″ drive bay into the front of the case, about one inch to the left of the drives. You can then add a second drive, a 720K 3.5″.
  • Install a hardcard for a 2nd hard drive (or first, if you don’t have one). I used a Plus HardCard 40 myself.
  • Install a Sound Blaster for some audio fun. For maximum enjoyment, use an original Sound Blaster 1.0 at IRQ 2 or 3, so you can get early programs with buggy SB support playing digitized sound, like Rise of the Dragon, Stellar 7, or Tongue of the Fatman.  (Rise of the Dragon has particularly nice opening digitized audio.)
  • If you can find one, try to obtain an AT&T PC 6300 memory board (with software .sys driver!) so you can have 2MB of EMS in the machine. It helps with Lotus 1-2-3, but it really helps as a giant disk cache.
  • For that matter, try to find the 6300 mouse. Moving the cursor around with a mouse in text apps that don’t support mice is a trip.

All of the above modifications will enhance your enjoyment of the 6300 while still keeping it distinctly 6300-ish. Some are difficult (dremel’ing a drive bay), but the effort is worth it.

Or, you can buy my 6300 off of me. For one meelyion dohlaars.

PS:  Original color or mono monitor broken?  The video output is analog, not digital, so you can wire up a VGA converter cable and use a VGA monitor.

Posted in Vintage Computing | 42 Comments »