On this blog, we previously looked at the original IBM PC 5150 as well as the much more advanced IBM AT 5170, but in this post, we are going to look at the machine IBM released in between those two iconic computers of the 1980s, the IBM XT 5160.
The IBM XT or IBM eXtended Technology was released in 1983, about two years after the original IBM PC 5150. Overall, the XT is more or less a small upgrade and refinement of the original PC. Many of these improvements were either refinements to the motherboard or simply included things in the stock configuration, such as a higher amount of base memory or the inclusion of a hard drive. The most impactful change from the PC to the XT, in my opinion, was the increase in ISA slots from the PC’s five to the now-standard eight. This increase of three 8-bit ISA slots gave a lot more wiggle room for expansion and set the standard for all IBM compatibles to come.
The case is extremely similar to the 5150 case in style and function, and you would be forgiven for confusing the two at first. There is a prominent IBM badge on the left side if you need to quickly confirm.
There are also two full-height drive bays on the right side of the case. Mine are taken up by two half-height floppy drives, a 360k 5 1/4 drive, and a 720k 3 1/2 drive, as well as a full-height 10MB MiniScribe MFM hard drive. Most models came stock with a full-height 360k 5 1/4 drive, as well as either a 10MB or 20MB hard drive.
Take note, most IBM XTs do not have screw holes for half-height drives, so you’ll need an adaptor or you’ll need to rig something up to secure the drives.
Looking at the rear, we again have mostly the same basic setup as the original 5150. The main difference is, of course, three more slots for expansion, but also the cassette deck connector port that was found on the 5150 has been removed on the 5160.
Before we take the top off the XT and look inside, let’s quickly talk about the monitor.
The monitor I chose to pair with my XT is the IBM 5153 CGA color monitor. The 5153 launched in 1983, the same year as the XT, and allows games to be played in 16 color digital RGB in CGA mode or low resolution EGA mode. Overall, it’s a great early color monitor and pairs well with an IBM PC or XT.
Taking the cover off reveals the inside of the case, which is very similar in appearance to the 5150.
The first image is the XT as I originally found it. The second image is the XT after I added the 720k floppy drive, as well as a few other upgrades.
After removing all the expansion cards, we can get a better look at most of the motherboard.
1 ) CPU – The CPU of the XT is the venerable 8088 running at 4.77MHz, which is the exact same CPU as was found in the original IBM PC. The CPU is even running at the same speed, with not even a built-in turbo option to 7 or 10MHz. It’s a great CPU, and there are a lot of early 80s games that run fine on it, even at stock speeds, but it’s one of the factors that make the 5160 not much of a step up from the 5150. For an easy and cheap upgrade, the 8088 can be easily swapped out with a 4.77MHz NEC V20 chip, which will slightly increase performance and retain extremely high compatibility with software.
2) FPU – Like the 5150, and many other 8088-class PCs, the IBM XT does provide a socket next to the CPU socket for the addition of an optional 8087 math co-processor. As far as gaming purposes go, adding an 8087 will have little to no effect in most circumstances, though there are a small handful of titles that an 8087 may improve performance.
3) Opps! I accidentally went straight to 4.
4) RAM – The 5160 originally came with a maximum RAM amount of 256k on the motherboard; later revisions of the motherboard allowed a full 640k on the board. My motherboard is an earlier revision with a maximum of 256k installed. ISA memory expansion cards could be used to increase the maximum memory to 640k on older revisions like mine. 640k was mostly sufficient for any games from the early 80s. Overall, memory limits are the same as they were on the IBM PC, with the difference being that the lowest stock XT came with 128k of memory, as opposed to the PC’s lowest stock configuration being 16k
5) Expansion slots – The increase in 8-bit ISA expansion slots is perhaps the most impactful and helpful upgrade the XT introduced. The slots available jumped from five on the PC to eight on the XT. This is especially helpful when you take into consideration that nothing was built into either of these machines, so you were already losing an expansion slot to a floppy drive controller, a video card, and possibly an HDD controller. Seeing as this was the early days of the PC and things like sound cards and such wern’t a necessity you certainly could manage with the five ISA slots but if you did want to push your systems usefulness and add more cards like a sound card, a hercules card to compliment the CGA card or add things like memory expansion cards, having the extra ISA slots of the XT was really nice.
Take note that slot 8 (closest to the power supply) is slightly different from the other seven slots and expects a “card selected” signal. This means not all expansion cards are 100% compatible with slot 8.
6) switch block – The XT was able to cut down the number of switch blocks from two in the 5150 to only one in the 5160. This block of switches is used to set things like memory amount, floppy drives, math co-processor, and video card type.
7) AT Power connector
8) PC Speaker
Cards and Upgrades
The first two expansion cards we will look at are the floppy controller and hard drive controller cards. They are basically the same cards that were found in the IBM PC. Since the XT did not have these features built into the motherboard itself, it required expansion cards.
The standard floppy controller uses an edge connector to connect the inner floppy cable, but supports both 360k and 720k floppy devices.
The stock hard drive for the XT was the MFM Seagate ST-412 10MB full-height drive; later models of the XT included a larger 20MB drive.
On my machine, the original drive was replaced with a Microscribe hard drive at some point.
Video
For a video card, you’re probably going to want to throw the same options as an IBM 5150 due to the same 4.77MHz CPU. Without an accelerator, the XT can’t handle most EGA or VGA games very well, so your best bet is a monochrome or CGA card.
My particular XT has a Paradise EGA card installed due to my accelerator upgrade that we will talk about shortly.
AST SixPakPlus
One of the best upgrades for an older 8088 IBM is something like the AST SixPakPlus or similar card. These cards offer more RAM so you can easily expand your machine to the full 640k, as well as adding serial and parallel ports, as well as a real-time clock.
I used a SixPakPlus in my machine so I could max my memory up to the full 640k. The card is also relatively small and easy to setup and use with its own jumper block.
Sound
I would say sound isn’t really necessary on an IBM XT, as the PC speaker is more than enough for games of the time. Sound cards didn’t really make an appearance until the late 80s, and by then, the 8088 was a little long in the tooth for games that supported sound. Nonetheless, if you do want sound or are using an accelerator, the most appropriate sound card would likely be an original AdLib card.
My original Adlib was being used in another machine, so I installed this excellent clone card that pretty much recreated the original card 1:1.
joystick/gamepad
For using a gamepad, I also installed an 8-bit joystick port card.
Accelerator
The final addition I made to my machine was an Orchid Tiny Turbo accelerator card.
The Orchid Tiny Turbo was specifically designed to work in machines like the IBM XT. It installs in the 8-bit ISA slot next ot the CPU and uses a cable to connect to the CPU socket once the CPU is removed and installed on the card.
The Tiny Tubro has a 7.2MHz 286 on board as well as a 287 math co-processor, which can be enabled via a switch on the card. This won’t make the machine quite as fast as a true 286 PC like the IBM AT, but it will give a SIGNIFICANT boost in CPU power, allowing the machine to play some of the more intensive games running EGA color and sound.
The Tiny Turbo can be set back to 4.77MHz 8088 mode so you can retain 100% compatibility with older software. Keep in mind, flipping the CPU switch while the XT is in operation shouldn’t cause any harm, but it will reset your PC.
That was a look at the IBM XT, IBM’s second machine for the home market. The XT is certainly an improvement on the original PC, but quite incremental. The most significant improvement is the addition of three more 8-bit ISA slots, making expansion much easier. If you love the classic IBM machines and want something for the early years, there’s no reason to go with the IBM PC over the IBM XT except nostalgia. That said, if you were having trouble running a particular game on the IBM PC 5150, you will have the exact same issues running it on the XT 5160. Overall, I’d still strongly suggest an IBM PC compatible clone over IBM’s offering for early 80s DOS gaming.
ancientelectronics 