The difference between an original IBM PC and a PC/XT seems subtle today. The XT wasn’t a huge upgrade over the PC, but the improvements were enough to be significant. The changes IBM made greatly extended the lifespan of the XT, and that’s one reason XTs are so much more common than PCs today. Let’s take a look at the IBM PC vs XT.
The PC/XT had the same CPU running at the same speed and couldn’t take any additional memory over the PC. But the XT was more expandable, and in the late 1980s, that was everything.
IBM PC vs XT: Similarities
Similarity-wise, the PC and XT had a great deal in common. Both of them were powered by Intel 8088 CPUs running at a modest 4.77 MHz. Both of them were expandable to 640K. They ran exactly the same software. The hardware was compatible too, since the expansion slots were electrically compatible and the cases were still the same size, so you didn’t even run into physical incompatibilities that you could run into with certain clones.
XT stood for “eXtended Technology,” and that was appropriate. The XT was just an extension of the PC that offered improved expandability. From a software standpoint, the machines were the same. And from the front, the machines looked almost exactly alike too. The easiest way to tell the difference between the two was from looking at the badge. The PC’s badge said “IBM Personal Computer.” The XT’s badge said “IBM Personal Computer XT.” The model numbers were similar too. The PC was model 5150, while the XT was model 5160.
In the mid 1980s when the XT was first introduced, the expandability was a luxury, not an absolute necessity. But as the decade wore on, it became more and more necessary. XTs has a longer useful life because you could plug more into them, even though they had painfully slow CPUs.
IBM PC vs XT: Differences
The PC came with a cassette port, which IBM removed from the XT. IBM figured some people might want a tape drive as a cheap storage option when it released the PC. It turned out people willing to pay for the IBM name were willing to buy disk drives, so the tape port went away with the XT.
But the most important differences between the PC and the XT were the power supply and the number of expansion slots.
The power supply
The PC came with a 63 watt power supply, which was adequate for up to two floppy drives, but not enough to reliably power most hard drives available in the early 1980s. The conventional wisdom was that if you wanted a hard drive in a PC, you needed to replace the power supply. It turned out that some hard cards, which consisted of a controller card and a 3.5-inch hard drive mounted right on the card, were low enough power to work in a PC. But that option came later.
The PC/XT came with a 130-watt power supply, which is wimpy by today’s standards, but was large for 1983.
IBM also gave the XT eight expansion slots, rather than the mere five the PC gave you. This was important, since neither the PC nor XT had much built into its motherboard. Putting everything in expansion slots made the machine very upgradeable, but five expansion slots quickly proved not to be enough.
Why not? You needed one slot for your video card and another one for your disk controller card. Initially, both the serial and parallel port usually came on their own cards. Once you added a memory expansion card, your machine was full.
Multifunction cards, which combined the serial and parallel ports and memory expansion onto a single card, opened up a couple of slots. But if you added a hard drive, its controller chewed up one of your slots. So you were full again, or close to it.
Why XTs had a longer useful life
The XT had a 130 watt power supply, which was more than enough to power a hard drive and a case full of expansion slots. With an XT, you could load a system up with two floppies, upgraded video card, a hard drive, a parallel port for a printer, a modem, a mouse, memory expansion, and still have a slot left over for a network card or sound card. Or two slots, if you used multifunction cards. Such a system was anything but state of the art but was useful into the early 90s. Even once they weren’t tolerable as a primary computer, offices would keep such XTs around as spares to use if another computer went down and needed service. And it was surprising how many DOS games into the 90s would still work on an XT if it had souped-up graphics and sound. It wasn’t optimal, but it worked. When I was working Best Buy in 1994, we still carried some interesting titles that would work on XT-class machines.
The PC is older and more scarce today, and therefore, more valuable, although there’s fairly substantial interest in any 1980s IBM computer these days.