Computer Restoration Ramblings
Resurecting an old PC-XT
I wanted to bring my old PC-XT into operating condition to be able to use it instead of trashing it or letting it sit on the shelf just taking up space.
Most of the hardware was operational. Software was available as well with plenty of spare boards and parts. It seemed a shame not to bring it all together and make it operational again. There was enough hardware to end up with a delux PC-XT configuration. Monochrome and color graphics, two monitors, a full 640k of ram, 50meg hard drive (configured as 30meg for C and 20meg for D), basica in rom, two serial ports, two parallel ports, real-time clock and a couple of 360kb 5.25 inch floppy drives all running at 4.7mhz on an 8088 processor.
A 1980 dream machine. Easily worth nearly $10,000 in 1980. Of course that was 25 years ago. Even ten years is an eternity in computer development years.
I finally found a standard MFM controller card and was able to properly install an old Tandon 10meg hard drive. The RLL cards did not work with the old MFM drives. I tried five of them and all drives failed to boot after an initial boot.
So what can you do with a 1980 dream machine? Whatever you do, it is very slow. Lotus2, Wordstar, a few games, Wordperfect, all running under DRDOS5 and the hard drive is already half full with only 5 meg of free space left.
Programs are installed using 360kb 5 inch floppies. Communications are through the serial ports. Modem and Laplink crossover cable to a second computer.
All programs are single applications and single user. There are some TSR programs but using them just eats up memory. With only 640k ram, programs have to be fairly small to run well. Even then the 4.77mhz speed is painfully slow.
All features other than the basics require .SYS files be loaded in memory at boot. These include any CDrom drivers, mouse drivers, joystick drivers, special floppy drive drivers, and ansi drivers. It is not unusual to eat up several hundred k of memory on the drivers alone. This risks leaving insufficient memory to run applications that require these drivers. It is almost always these driver hungry applications that also require the most memory to run.
The main features going missing are networking, good fast graphics, and high speed execution of programs. There are considerable lag times for any disk access including hard drive. No email or internet browsing. Outside communications are limited to serial modem dial-up services and small efficient terminal programs. No fancy color graphics or modern browsers.
The speed can be improved somewhat by using a turbo board running at 8mhz, but that is still very slow divided by two. There are also some software incompatibilities when using a turbo board.
The good news is that all those old basic programs work very well. Basica, GWbasic, and other versions are available to run and easily create all kinds of programs.
Where do we go from here. Well, the computer industry thought that the 286 was a natural improvement. Going from 8 bits to 16 bits is an immediate X2 speed improvement. 286 machines were also capapble of higher clock speeds with some of them going as high as 20mhz. So you got twice the computing power by going to 16 bits and up to five times that by multiplying the clock speed by five. That would get you a computer almost 10 times faster than an 8088 XT and it was also possible to add extended memory.
I have a 286 motherboard with coprocessor, and 1meg on-board memory. I also have a 2meg ems memory expansion board. Clock speed on this processor is 16meg and it will help solve the speed problem but it will still be a single user, single application computer.
It needs a case, power supply, cmos backup battery, and a some configuration work.
True multitasking and useful extended memory was not possible until the 386 processor. I have one 386 board and one 486 board. Both of these would build a computer far more capable than the 286.
It may be useful to build a 286 into the old, large, 286 computer case. At least that would provide the case and power supply.
Although there is ELKS linux which claims to work on a 286 processor, Linux is really better suited for 386 processors and better, with at least 16meg of ram. Linux solves the network problem and the more capable processors solve the speed and ram limitations.
The easiest solution to the networking problem is to use win95, win98 or Linux. Smaller and older versions of Linux can run on as small as a 100meg hard drive. Puppy Linux requires at least 250meg of fat32 hard drive space on a windows partition. This is not normally a problem because the minimum sized hard drive space required to create a fat32 partition is 520meg. Win95, and Win98 will need at least 250meg of hard drive space. All of these operating systems also require a CDrom drive and a 3.5 inch floppy drive. Windows also needs at least 32meg of ram and a minimum of 65meg of free hard drive space for a swap file. So, although windows can be installed on a 250meg hard drive, you need at least twice that to build a usable system.
Solving the file support problem for a non-networked computer, like the PC-XT, is best handled by having other computers that support the PC-XT floppy disk format. The PC-XT has two 360k floppy drives (one of these may soon be removed, only need one). The NONE computer now has a 1.2 meg 5.25 inch floppy drive which is accessible over the network. The SPEEDY computer now has a 360kb 5.25 inch floppy drive which is accessible over the network. Software can now be downloaded on any of the networked machines from the internet. That software can be shared over the network and written to either 1.44meg 3.5 inch, 1.2meg 5.25 inch, or 360kb 5.25 inch floppy disks. The 360kb disks can be read directly by the PC-XT. Also have software tha will split files between disks. So if there is a file too large to fit a single 360kb floppy, it can be split between two or more disks.
All three floppy formats can be read and written from any of the networked computers. Floppies can only be formatted on the machines where the drives are installed. Care must be taken to ensure that there is a floppy in the drive before network access can be accomplished.
Just spent far too much time on an old 486DX-66 motherboard. The memory was bad. This board is a good candidate for another router/firewall.