Oldskooler Ramblings

the unlikely child born of the home computer wars

The Care And Feeding of the M24/6300/6060/1600

Posted by Trixter on December 9, 2021


The Olivetti M24 was a fantastic PC compatible that was double the speed of the IBM PC, had built-in expansion ports, a smaller footprint, and special hi-res graphics, all at a price cheaper than the original PC. AT&T brought the M24 to the USA and sold it as the AT&T 6300, and it was very popular over here as an alternative to the PC. (Xerox also imported it to the USA and sold it as the Xerox 6060; in France, it was sold as the Logabax 1600.)

As the vintage computing hobby continues to grow, a lot of people have been coming across these and wondering if they should take the plunge. While the 6300 is among my most favorite systems ever made, I usually don’t recommend it for beginners because it uses a proprietary keyboard and monitor, and if you don’t have both, it can be extremely difficult to adapt a traditional keyboard and monitor for use with the system unit. But, if you see one for sale for cheap, and it has everything and works, I’d like to offer some modern tips on the care and feeding of these unique beasts. These hints can help get your system up to speed as a useable and practical member of your collection. (Note: When I write “6300”, I’m talking about all versions of the Olivetti M24, as they were identical hardware.)

Preparation

First and foremost: If you have a working system, IMMEDIATELY power it off, open it up, disassemble it, remove the motherboard from the bottom of the system, and carefully desolder and remove the barrel battery. It’s not needed to operate the system, and can only cause permanent failure if it corrodes the motherboard. (You can try to snip the battery off with snips, but I have broken a motherboard this way so I usually recommend the gentler option.)

If your system boots up with a ROM BIOS other than 1.43, flash the 1.43 ROM BIOS and install it. It fixes some bugs. There is an associated PAL that came with the ROM BIOS upgrade kit, but in my experience it wasn’t necessary to operate the machine (some of the hardware support introduced by 1.43 won’t work without the updated PAL, but the rest of the BIOS enhancements will work). One thing the upgrade gives you is the ability to run Microsoft Word for DOS 4.x and higher in graphical mode using the 6300’s high-res graphics.

If you don’t care about running GeoWorks Ensemble, replace the 8086 with an NEC V30 for a 20% speedup. Ensemble will no longer work for some reason, but everything else will feel zippier.

Storage

If you want to add an XT-IDE, you need to use any XUB BIOS made in the last 2 years or newer, because it has speed-optimized code that deals with the bus issues of the AT&T. The speedup is minimal, so if your XT-IDE card works as-is, it’s using the slow compatible mode and you may want to leave it that way so you can use it in any system.

Bus issues? Yes, unfortunately on the 6300, doing a word-sized read or write will accidentally transpose the values. This causes some software to break. A “bus correction kit” was available that fixed this, but they are rare. An effort on the VCF forums was made to reproduce them, but I don’t know where that project landed; sorry. If your XT-IDE card is using the wrong BIOS that tries to do word-sized reads, you may see it start up with endian-swapped lettering when it identifies the CF card: Instead of your transcend CF card showing up as “TRANSCEND”, you’ll see “RTNACSNE D” and then it will hang. Flashing a new XT-IDE XUB BIOS using the most compatible options will fix this.

You can put any 3.5″ drive in the system and get free 720K DSDD support by ensuring you have a DEVICE=DRIVER.SYS line in CONFIG.SYS with appropriate params for 720K. But that’s it; the built-in controller does not support high-density drives. You’ll have to get a replacement floppy controller and disable the onboard one if you want to do that, but IMO it’s not worth it when XT-IDE makes transferring files with modern systems easy.

Networking

Intel Etherexpress 8/16 network cards don’t work in an AT&T because of the bus issue mentioned above. Xircom parallel-port ethernet adapters work fine, albeit slowly. I’ve used other period-appropriate ethernet cards with success, although I prefer to use anything with an RJ-45 connector as I find 10 base-t ethernet transceiver dongles cumbersome.

Keyboard

The keyboard, and it’s plug and signaling, are proprietary. It is nearly impossible to use a different keyboard. There is someone on the VCF forums who came up with a hardware design to translate the signaling between the 6300 keyboard port and a PS/2 connector, but I also don’t know where that project landed, sorry.

Display

The display adapter is proprietary; it outputs a high-res 25 KHz horizontal signal, but that can only be used with select AT&T monitors. It also provides voltage (!) to power AT&T monochrome monitors. Trying to replace it with something like VGA is difficult and frustrating, especially if you don’t have the bus conversion kit mentioned earlier. My advice is to try to keep the original monitor running, as that is part of the system’s charm.

If you can’t find a working monitor, you can use an RGB2HDMI and a custom adapter to translate the signal to HDMI. It’s an RGB TTL signal that runs at 56Hz vertical and (if memory serves) 25KHz horizontal, and provides a 640×400 display.

Speaking of that display, it had more support than people realize. You can run Windows 3.0 in real mode, Geoworks Ensemble, and GEM in 640×400 if you like graphical environments.

Power

The power supply is very odd (24 V?) and is difficult to repair because it is built in two halves. It also houses voltages that can injure or even kill you if you open it up and try to repair it. Be careful, and refer to the Olivetti M24 technical reference or the 6300 Sams Computerfacts to know what you’re getting into.

Enhancement

The dimensions of the system are proprietary; they will not take replacement motherboards. In fact, the motherboard and the bus interface are two separate backplanes that interface through the display adapter (you read that right: The display adapter) so it’s impossible to adapt the case to house anything else.

I do not know which accelerator cards (ie. 286 or 386 speedup cards) work in a 6300. My guess is that most of them would not work because of the aforementioned bus issue and/or expecting an 8088 when the system uses an 8086. The only accelerator cards that are likely to work are those that didn’t use a ribbon cable to replace the CPU, such as Applied Reason’s “PC-elevATor” board.

Most, if not all, 8-bit sound cards work just fine in a 6300 as they didn’t require word-sized accesses. I recommend an 8-bit Sound Blaster clone, or a Sound Blaster Pro. DMA on those cards works fine and you can even play MOD songs on a 6300 at 24Khz or higher with one. You can also use an LPT sound dongle (ie. Covox) as there is nothing particularly odd about the 6300’s built-in parallel port.

You can put EMS cards in 6300s and they work. EMS boards are slow in the 6300 unless you get the AT&T-specific, AST-made, EEMS 3.2 board, which uses the proprietary 16-bit wacky interface unique to the AT&T, and then the EMS memory is the same speed as the main memory (and enables some other neat tricks, like expanding lower DOS RAM from 640K to 736K). Desqview also runs very well with this board installed, although a regular EMS board helps with that too.

One Response to “The Care And Feeding of the M24/6300/6060/1600”

  1. The 6300’s 640×400 graphics mode was also supported on the GRiD 1500-series portable’s internal plasma/LCD display (BIOS video modes 40h, 48h, and 74h). The technical reference documented them as being “compatible at the ROM-BIOS level” rather than exposing the same hardware registers.
    https://github.com/philip-searle/gridcase-bios/blob/main/src/video.inc#L40

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