 The magazine of the Melbourne PC User Group The Hare and the Tortoise - Upgrading Your Old XT Greg Eden |
Are you reading all the magazines and lusting after 33 MHz 386 machines, but can't afford or justify the expense? Still, the old 4.77 MHz 8088 is getting a bit tired. Well, for around $400 you can do wonders. I recently upgraded my motherboard to a 286 XT. That's right - XT, not AT. This modification will not make your computer into an AT, but it will make it into a Hare that will leave the Tortoises in the dust.
The Octek XT 286 is a motherboard replacement for XT's. I purchased mine from Pacific Microlab in Box Hill. They are also available from several other outlets around Melbourne. The board is only half the size of a normal XT motherboard, although it fits in any standard case. I have mounted one in an old XT and one in a small footprint box and both fitted without problems. The CPU is a 10 MHz 286 and the bus is an 8 bit XT bus. It can be fitted with up to one megabyte of RAM. Unfortunately your old chips will not fit, as 424256 memory chips are required. The price of these chips is dropping. If you shop around they can be obtained for $20 a chip (one megabyte is 8x20=$160). The motherboard is priced at $249. These prices are current at time of writing (March '90). The RAM chips may be cheaper by the time you read this article.
Your old box probably does not have a Turbo Light or a Turbo Switch. The simplest solution is to connect the power light to the turbo light connector and put a jumper on the turbo switch connector. Then use <Ctrl><Alt><+> or <-> to turn the turbo on and off. Use the grey + and - keys on the numeric keypad. You can buy LEDs and switches and start drilling holes, but it is not necessary. <Ctrb<Alt><Esc> resets the system speed to the system default defined by the turbo switch, generally that would be turbo. This is occasionally required after prolonged floppy access. One oddity is that the BIOS turns off the turbo when the system accesses a floppy drive. This leads to the turbo light flashing as a floppy formats or data is read. At first I thought that a fault existed, however the board is designed that way.
The RAM above 640 kB is not EMS or AT extended memory and as such can only be used by the utilities that come with the board. The memory is physically identical to AT extended memory, however the BIOS does not support the AT specific calls required to use standard AT utilities. The utilities provided are a print spooler, a RAM disk and a hard disk cache. They all seem to work fine, although the disk cache has failed to operate on other machines I have seen. Another problem is with old clock and CGA cards, they may not cope with the speed of the system, it depends on their age. EGA and VGA cards work well.
It is possible to use an EMS emulator on the extra 384 kB of memory (I will upload one to the Bulletin Board). This fix is neither as fast nor as flexible as the real thing. If you use EMS you would be better off to move up to a NEAT AT and ignore this board. The system also includes a Shadow BIOS. A Shadow BIOS is a system of relocating the system BIOS in RAM, to speed up access. However I scrambled my hard disk when I defragmented it under the Shadow BIOS, so I reset the DIP switch that sets the board to default to Shadow BIOS. Many causes could be to blame, but I have left it off just in case. The Shadow BIOS can be turned on with software through a line in CONFIG.SYS. This is the method I now use, so I can override it by booting from a floppy.
Does this modification do much for your computer? You bet!! How does a Norton SI of 11.0, and a Landmark Speed of an AT at 12.3 MHz grab you. The manufacturer of the board claims it is the functional equivalent of a 31 MHz XT. The hard disk cache also speeds up my old Seagate to a rating of 3.7 on the Norton SI test.
With the cost of ATs dropping you need to think carefully before grabbing your Bankcard and rushing out to buy the XT 286 board. Remember the tortoise won the race. You may be able to sell your old XT and buy a base AT for not much more than the cost of this upgrade. Of course your old XT is also worth a lot less than it was, a 4.77 MHz machine is worth almost nothing when a new
10Mhz XT is selling for $750. If you have a fair bit invested in a XT, such as a hard disk and maybe an 8 bit VGA, then the Octek XT 286 may be the upgrade for you. Then watch out tortoises!
Reprinted from the May 1990 issue of PC Update, the magazine of Melbourne PC User Group, Australia
