Oldskooler Ramblings

the unlikely child born of the home computer wars

Beefing up your AT&T PC 6300

Posted by Jim Leonard 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 a 7.16MHz 8086, about 1.7x the speed of the IBM PC’s 4.77MHz 8088
  • The graphics mode could go 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.

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32 Responses to “Beefing up your AT&T PC 6300”

  1. zpinzane said

    This post is ridiculous yet awesome. It is definately not Y1992 complaint. But that’s ok.

    Mmm. Rise of the Dragon.

  2. Chris said

    Back in 99-2000 or so when I was working at a computer store as a tech one of these beasts came in for repair. I remember my boss (true oldskool, he founded a company and built a line of cards for S-100 machines and even a few S-100 computers, maybe a future oldskool.org feature ;)) warning us about the whole power goes thru the monitor port deal. The only thing I can remember about the inside of the machine were two giant power leads going into the motherboard. I think Windows 1.0 supported that 640×400 video mode too.

    Whats really scary is that I still see XT class machines come in for repair at that store, particularly the Leading Edge Model D (store was a major dealer back in the day). Some people just don’t see the need to upgrade I guess.

    Jim, you still haven’t gotten those IIgs Silpheed clips up…. its been almost 10 years (ya rly!). I actually found the original samples I sent you on an old harddrive. Or put up that Copy II PC Option Board page up, I found those cards sitting with the hard drive!

  3. Trixter said

    Chris: I just ran across the clips the other day :-) I think the Sound Card Museum will have to go up first, and before that I need to finish up MONOTONE, but maybe THEN we’ll have a Silpheed page :)

  4. Carlo said

    I am trying copy II PC Option Board Central Point Software. you could help me please. Thanks Salutes

  5. [...] blanked, but moving over to that side of the room it turned out to be an AT&T PC 6300 WGS. I’m a bit fond of AT&T 63xx machines, so I went over to [...]

  6. Yuhong Bao said

    BTW, you should look at the AT&T 6300 Plus. It was a 286, but what was interesting was that it contained extra hardware that tried to work around the problems of 286′s protected mode. It was used by OS-Merge running under Unix.
    http://www.extremetech.com/article2/0,1558,1177797,00.asp

    • Yuhong Bao said

      In fact, it was completely hardware incompatible with the PC/AT, which means that protected-mode OSes written for the PC/AT will NOT run.

  7. Mr. Zorbatron said

    I have two AT&T memory boards in my machine, using both of the two 16 bit slots. Where would one obtain such .sys driver for EMS?

  8. Trixter said

    I’m afraid I don’t know; you should ask the folks over at http://www.vintage-computer.com/vcforum/

  9. really_old_geek said

    Okay, I am *really* scared I came across this post. You see, I am cleaning up and found some of my old systems. They include a 6300 and 2 6300PLUS units along with 2 monochrome (313) and 1 color (318) monitors. Now I *gotta* sse if they still work. Hope I can remember (or find) information on the switch settings, controller cards, etc.

    I just had to thank you for the smile.

  10. kaputt said

    I just pulled my PC 6300 out of the garage. It did not boot up the way I remember. The Caps Lock and Num Lock lights keep flashing. I remember this meant something, but for the life of me, I can’t remember what. How long should it take for it to boot up? I have the DOS on the hard drive, or at least that’s the way I remember it. I’m going to let the BIOS battery charge and try again later.

    One of the things I remember about this computer, is that on some games, I had to use a program called slow, to slow it down enough to play. My friends didn’t need this on there computer. :)

    • Trixter said

      I remember that too, and it’s generally not good. Give me a day and I’ll look that up in my tech ref.

      • kaputt said

        Thanks. I’ll try to find my manuals, but it might take a while.

        • Trixter said

          Okay, I have my PERSONAL COMPUTERS PC 6300 T231 Service Manual (from your friendly neighborhood AT&T Information Systems SERVICES DIVISION EDUCATION department) right here next to me and there’s an entire section on diagnostics. Let me check it a bit…

          Nothing on flashing lights specifically, but it says that you need to have, at a bare minimum, the following working for the onboard diags to start up on the display:

          8284 8-MHz clock generator

          LS244 clock driver

          8288 bus controller

          A minimum subset of the 8086 CPU’s commands must be functional

          The two ROMs, as well as the data address and control buses to the ROMs, must be functional

          Note that RAM is not part of those requirements, so even if no RAM is installed the thing should start through it’s diags. The manual states that the sequence at startup jumps to the CPU test, then the CPU is tested for basic functionality, then the keyboard peripheral interface chip (8041 or 8741) is programmed and initialized, and THAT is when the lights go off and a beep is heard. Are you getting that far at all, or do the lights flash all the time without a beep?

          …Hey, there’s a later section on maintenance that goes into troubleshooting if the system test can’t be run! Using this section and your description of “numlock and capslock lights constantly blinking”, that points to the table “no display, LED okay, fan okay, no beep” which says “Replace the motherboard”. :-( :-(

          I would reset your CPU and ROM and memory chips before you toss it. Even if you do decide to toss it, do the community a favor and sell it on ebay for a buck or something so that another 6300 owner can use it for replacement parts.

          • kaputt said

            Thanks for the reply. I reset every chip I could underneath. Still same problem. The BIOS is on EPROMs, right? Don’t they go bad after a certain amount of time? I mean, even with labels over the window, UV rays would still erase them maybe, I don’t really know.

            I certainly wouldn’t just throw it away. My intension was to get the files off the hard drive and then sell it for whatever I could get so that someone else could enjoy it. I just have to figure out how to get the files. The hard drive has an edge connector I think I remember. (I should have looked when I had it open.) That will make it difficult.

            I found my manuals. Not much help.

            • Trixter said

              Last-ditch effort, you could try asking the folks at vintage-computer.com in the forums; there might be one or two AT&T PC 6300 people still there who could help. I think the troubleshooting grid in my service manual has the correct advice, sadly (“replace motherboard”), but maybe someone there knows something I don’t.

              In any case, they can also help with advice on getting data off of the hard drive. If you have any other machine with ISA slots, you might be able to transfer both the controller and the drive to another machine (since the drive is either MFM or RLL, it’s important to keep the controller with it, as the controller definitely understands the low-level format on the drive, and other controllers might not).

  11. koz said

    While cleaning out some old junk boxes, I found a small 3-ring binder that says, “Service Manual AT&T Personal Computer 6300″ – inside, it has a bunch of 5 1/4″ floppy sleeves containing disks with DOS (Ver. 3.30), AT&T Tutorial Disk, Customer Test Diagnostic Disk (Ver.2.03, and Ver. 3.18), System Test Diagnostic Disk (Ver. 3.18), Low Level Format Utility(Ver. 3.18), and a 3 1/2″ floppy containing DOS (Ver. 3.30). Alas, I have no computer to use them with. I used to have an old Zenith computer that they may have worked with, but it’s gone now.

    • Trixter said

      If you still have the binder and disks, I’d be happy to reimburse you shipping if you’d like to donate them to a good cause. If so, email me using trixter(@)oldskool(.)org.

  12. Simtech Orlando said

    I’m judt getting my 6300 going again

  13. Alex Dillard said

    An AT&T PC 6300 has been sitting in my closet for probably 7 years or so. Before I try to get the 6300 going again (it’s a two 5.25 floppy drive model) I thought that for backup purposes I would try to make image files of the ‘critical’ 360k 5.25 floppy disks. It would be very interesting to know what sort of hardware/software arrangement was used to create the images at ‘https://sites.google.com/site/att6300shrine/Home/downloads’. Unless I am mistaken you recorded some of those images, so if you can shed any light on that please do. I don’t have any prior experience making images of anything other than hard drives, and that’s on very recent hardware. Imaging floppies is a bit more foreign to me. The software candidates that I have identified so far are: Rawrite (http://fdos.info/ripcord/rawrite/), DskImage (http://www.brutman.com/PCjr/pcjr_downloads.html) and WinImage (http://www.winimage.com/). So far I have secured a working 360k 5.25 drive and a ‘universal floppy cable’ to connect it to my Windows XP machine (who’s BIOS, to my surprise, appears to be able to correctly communicate with THE 5.25 drive). Do you think Windows XP is a good platform for imaging floppies, or should I get a copy of something else like DOS running? Any comments/advice/information you are willing to share would be greatly appreciated.

    • Trixter said

      The dskimage link on Mike Brutman’s page will do the imaging job just fine. If you’d like to use the actual tools I wrote, they are at ftp://ftp.oldskool.org/pub/misc/DISKUTIL.ZIP but the output will be the same so it’s your choice.

      You’re correct that Windows XP can talk to a 5.25″ 360K drive — in fact, so can Windows 7. You just need BIOS support for it. I would not try to image directly in Windows with the above tools; instead, I would either use Winimage (just make sure to save to an uncompressed raw format), or if you want to use the DOS tools, make a “windows xp boot disk” (it’s a pulldown option when you format) on a 3.5″ floppy in drive A:, boot from it, and then image from the 5.25″ drive to the 3.5″ disk. A 1.44mb disk will hold 3 5.25″ 360K images (possibly more if you compress them, so maybe copy pkzip.exe onto the 1.44MB floppy).

      Honestly, any method is acceptable. Winimage costs money but works fine in Windows. Rawrite is free and should also work in Windows. My util is flexible and faster than rawrite but only works properly when booted to DOS. Choice is yours.

  14. Alex Dillard said

    Here is a question that I would expect is relevant to most, if not all, 6300 owners: given that the monitor and keyboard used with the 6300 are proprietary, is there any hope of connecting a more standard monitor and/or keyboard to a 6300.

    The keyboard of the 6300 is quite specific (integrated mouse connecter and so forth…), so connecting something like a contemporary PS/2 keyboard to a 6300 is probably non-trivial. My guess is that not only are the connecters different, but the communication protocol is different as well (and right now I don’t have the slightest idea where to find documentation on the 6300’s keyboard protocol). [http://electronics.stackexchange.com/questions/7227/adaptor-to-use-old-att-keytronic-keyboard-with-db9-connector] If this is true then connecting a new PS/2 keyboard would probably require either a microcontroller or some sort of purpose-built translation circuit.

    For the monitor it would appear that the situation -may- be somewhat simpler, as connecting a modern VGA CRT or LCD looks to be simply a matter of using an appropriate interposer connecter [http://m24.museodelcomputer.org/docs/video_converter.pdf]. (I haven’t tried it yet – it isn’t clear to me what the risks to the hardware are should it not work.)

    • Trixter said

      Connecting a different keyboard is extremely difficult because it uses XT signaling (so PS/2 keyboards are out, unless you have one of the homebrew PS/2->XT adapters; check http://www.vintage-computer.com/vcforum/showthread.php?15907-AT-to-XT-Keyboard-Converter for details). The keyboard was also fed additional voltage from the computer, so you may have to account for that as well (if simply ignoring it doesn’t work). If you want one of those homebrew adapter PCBs, you’d better move quick because there was only one left as of this writing.

      You are correct that connecting any VGA monitor to a stock 6300 is not only possible, it is easy! The mode used by the M24/6300 was double-rate (horizontal is 31.5KHz) which is compatible with VGA. You can literally wire up an adapter and it will work without any modification. The site you linked to is based in Italy and is slow, but last I checked it was working. http://m24.museodelcomputer.org/docs/video_converter.pdf is the correct diagram for the VGA adapter.

  15. Dji Dji DjiBooty said

    Psion Chess also supports the PC 6300′s high-resolution 640×400 video mode. Just press “O” for Olivetti at the opening menu.

    • Trixter said

      Never knew that, thanks! I’ve added it to the 6300 shrine at https://sites.google.com/site/att6300shrine/Home

      • Dji Dji DjiBooty said

        Yeah I just found out by accident looking for DOS CGA compatible programs. You might want to start a list of software that’s compatible with the AT&T/Olivetti High-Res mode. I know Microsoft Word 5.5, and GEM and all it’s programs (1stWord Plus, Paint etc) work. Another little known fact about this video mode is that Toshiba included it on a bunch of their laptops from the late 80s/early 90s. Toshiba called it “Double Scan CGA” in its documentation, but it’s really just the PC6300 mode.

  16. JoeSnow said

    Does anyone know where to get a replacement CMOS battery for a PC6300 Plus? Mine is completely dead and I think my machine won’t boot up without it.

    • Alex Dillard said

      Interesting. I was under the impression that the battery in the 6300 was only needed to keep the clock working while the computer is off (which — I think — would be in contrast to modern PCs, where often the battery is needed to maintain all of the settings that are in the CMOS BIOS.) Anyone please feel free to correct me if I have stated something that is false. I’ll take a look later at the 6300 service manual (https://sites.google.com/site/att6300shrine/Home/downloads) and see if it says anything about the machine not booting specifically because the clock battery isn’t any good. Note that the battery you are referring to was mentioned briefly in comment #10 above, for a similar reason (“won’t boot”), although the ultimate conclusion in that instance appears to have been that the battery was not the issue.

      • Trixter said

        Unfortunately for Joe (Hi Joe! Email me for some Tandy fun!), the 6300+ was indeed a 286-based system which used a battery to maintain the CMOS. More unfortunately, I don’t have any information on the 6300+, sorry.

  17. DQ said

    ok came across this site beacuse I found an old AT&T 6300 Compaq “portable” computer that I used to use when I worked @ AT&T. It is quite large and has a handle. The keyboard comes off to reveal the screen & 2 floopy drives. I turned it on today and it started to boot up, but the date was 1984! So, I tried to enter today’s date and it wouldn’t accept it – which I knew would happen (having worked on computer programs during the big Y2K hoax!) anyway, I entered an earlier date, but then the time was showing 0:00:00 and wouldn’t let me enter any numbers. Anyone have any idea how to get past this? Saw some earlier posts about a battery for the clock… could that be the problem? Would love to get this computer booted up to show my kids. They can’t believe this is what the earlier PCs really looked like!

    • Trixter said

      I’m somewhat at a loss to answer you because you describe something I don’t think existed — there was no portable 6300 that I have ever been aware of. What you’re describing sounds like a Compaq Portable (in working condition, so kudos for that).

      It’s likely the DOS disk you’re booting is 2.x which may not support the correct date. If you boot a more recent version of DOS, such as 3.x or later, I believe dates past 2000 are possible. However, you don’t need to enter the correct date to use the machine; just hit ENTER twice when it asks for date and time, then continue to use the machine as normal. Also, there is no battery-backed clock in that model of computer.

      If you have an actual AT&T PC 6300 (not portable), then there IS a battery-backed clock on the underside of the motherboard that should have its battery replaced immediately as it is likely leaking. For that clock, the dates are limited from 1984-1992, so every time you boot up, the year is wrong. There are some hacks and fixes for that in the files section of the AT&T 6300 shrine at https://sites.google.com/site/att6300shrine/Home/downloads

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