Someone asked me recently to help them identify the type of keyboard they needed. And I realized that some of the keyboard connector types that used to be easy to find, common, and common knowledge are no longer any of those things. And then I realized that this is an area that is still changing. So let’s go over the common keyboard connector types or types of keyboard connections.
Keyboard connector types
There are a relatively small number of types of keyboard connections, at least when it comes to the plugs. But just because the keyboard fits doesn’t necessarily mean it’s compatible, so you need to be careful. In a few cases the pinouts are different enough to cause damage to the system. I’ve noted these instances where I am aware of a potential problem.
Once you venture outside the realm of PC keyboards, exercise caution when you don’t have a keyboard original to the system. You can make an expensive mistake if you aren’t careful.
USB is the most common keyboard connector type today. This is a standard that’s been around since the late 90s, and it replaced several legacy connectors that were used for various peripherals, not just keyboards.
The most common connector is still USB-A, the connector that has been around since the ’90s. Keyboards don’t care about the speed, just whether the connector fits.
USB-C is just a newer form of USB. It’s faster, not the speed matters for keyboards. The nice thing about USB-C is you can plug it in upside down, and it fits, and it works. With USB-a, you have a 50% chance of getting it right, but it sure seems like we manage to get it wrong more like 75% of the time.
The other advantage to USB-C is that it is much smaller, which is an advantage on portable devices. You can fit more USB ports into the same space, or you can make the device smaller.
You can get an adapter from USB-A to USB-C to convert a keyboard from one to the other. I don’t especially like typing on my phone, but if I’m going to type anything of any significant length, I use a USB-C adapter so I can use any USB keyboard to type.
The PS/2 connector made its debut in 1987, and it quickly became the most common type of keyboard, at least on name brand computers. It used a small round connector with a plug called a mini DIN plug that had six pins. The connector only fit one way. It is still one of the most common types of keyboard connections.
Confusingly, the PS/2 mouse used exactly the same connector, but the two were not compatible. I never broke anything by reversing the two, but neither of the keyboard nor the mouse worked if you did.
The other disadvantage was that the PS/2 port was not designed to be hot pluggable. You really weren’t supposed to plug and unplug a keyboard while the computer was on, although we certainly did. USB, on the other hand, was always designed to be hot pluggable.
Electrically, the PS/2 connector worked the same way as its predecessor, the plug was simply smaller. The design goal was to allow smaller, more compact, and sleeker looking desktop computers.
Computer manufacturers have been phasing out the PS/2 connector basically since the turn of the century, but to say it has been a slow ramp down is an understatement. Not all desktop computers have PS/2 ports anymore, but if you ask for one, you can almost always still get one as an option.
Converting between PS/2 and USB keyboard connector types
There was a time when keyboards that spoke both the PS/2 and USB protocols were available, and they came with an adapter that just changed the connector, and the keyboard would auto sense which protocol to use. These types of keyboards aren’t very common anymore, so if you find one of those adapters and plug it in to any random USB keyboard you have laying around, don’t be surprised if it doesn’t work.
You can get adapters that convert PS/2 to USB using active components, and the compatibility with those is nearly 100%. Just keep in mind those adapters cost more to make, so they cost around $15. If you find an adapter for, say, $5, it’s probably passive and compatibility will be very hit and miss.
The AT keyboard standard dates to 1984. It originated with the IBM PC/AT, from which it got its name. Early AT keyboards had a different keyboard layout then today, with 84 keys or thereabouts, and no separate cursor key pad. Later AT keyboards used the now familiar 104 key layout, or something similar, depending on when it was made.
AT keyboards use a round five pin DIN connector. Electrically it is the same as the PS/2 connector, so you can get an adapter to change between the two, and compatibility isn’t an issue. The PS/2 connector has an extra pin, but that extra pin isn’t used for anything.
There was a prior, and incompatible, standard that used the same five pin plug. The way to distinguish them is to look at the keypad. An AT keyboard will have LED indicator lights above the keypad for numb lock, caps lock, and scroll lock. The other keyboard type (XT) will not.
The XT keyboard standard dates to 1981. It was the keyboard standard that the IBM PC and its successor, the XT, used. The plug is the same and so is the pinout, but the protocol is different. You generally cannot interchange the two. I know I had a friend who used an XT keyboard on a computer with an AT connector, and it worked, but I do not know if it was a fluke.
XT keyboards are not at all common today, and for some reason, it seems an awful lot of XT computers got separated from their keyboards over the years, and for some reason, it seems like more of the CPUs survived. It is possible to buy an adapter to convert an AT or PS/2 keyboard to work on an XT, and that is usually cheaper than buying a proper XT keyboard if you need one.
The Tandy 1000 used an 8-pin DIN connector similar to the XT and AT, but of course, it wasn’t compatible with either. There was a time when millions of these keyboards existed, because it was incredibly popular, possibly the second best selling computer of all time.
If you have an early Tandy 1000 model with a round connector with 8 pins, don’t make the mistake of overpaying for an XT keyboard, because it will fit but it won’t work. Either overpay for a Tandy keyboard, or you can get a converter that adapts a cheaper PS/2 keyboard to work.
Later Tandy 1000 models from 1989 to 1992 adopted the PS/2 connector, and fortunately, a regular PS/2 keyboard will work with those later models.
IBM PC Junior
The ill fated PC Jr used its own keyboard, because of course it did. The connector books like and RJ11 phone jack on the keyboard side, and pin headers on the computer side. This is one of the more obscure types of keyboard connections today, since about half a million PCjrs sold through the years.
There were some aftermarket keyboards produced in the 1980s, but they aren’t exactly easy to find today. Generally speaking, I have less trouble finding a PC Junior keyboard than I do finding an XT keyboard. A lot more of those were produced, but there is a lot more demand for them as well.
Selected non-PC types of keyboard connections
I am going to miss a number of these, so if I miss the keyboard connector type for your favorite vintage computer that isn’t a PC, I apologize.
Apple used a keyboard connector it called ADB, for Apple Desktop Bus, for about 10 years. It was the keyboard connector type for the Apple IIGS as well as the Macintosh SE and later Macintoshes, up to the last beige G3 model of the late 1990s.
This connector has a round mini DIN plug somewhat similar in appearance to the PS/2 plug, but the layout and function of the pins is different. Physically, the connector is the same as the connector we use for s video. Don’t try to interchange ADB and PS/2 keyboards. The number and layout of the pins is all different, so you’ll mangle the plug.
Unlike the PS/2, Apple’s ADB connector works for either a keyboard or a mouse, and even allows you to daisy chain the mouse to the keyboard, making cable management more than just a little bit easier. Apple replaced ADB with USB starting with the first of the models that weren’t beige. Adapters existed to let you convert ADB to USB to use them on newer models if you wanted.
Mac 128 and 512
Early models of the Macintosh use a phone style RJ10 connector and plug, but please don’t make the mistake of using a phone handset cable. The pinout is not the same on both sides, and you will damage your keyboard. The chip that takes the damage is no longer produced and no longer available, so you will be shopping for a new keyboard. If you are missing the original cable, be sure to get a replacement cable designed expressly for Apple Mac keyboards.
And don’t try to plug a Mac keyboard into an Amiga 1000, or an Amiga 1000 keyboard into a Mac. Besides being incompatible, the power and ground connections are reversed, so you will damage the keyboard.
Much like the early Macintosh, early Amigas also used a phone style RJ10 connector. I don’t know what will happen if you try to plug an Apple keyboard into an Amiga or an Amiga computer into a Mac, but I don’t recommend you try it. The power and ground pins are reversed so you’ll damage something. I just don’t know what.
Commodore change to the keyboard connector type three times, so not quite every generation, but the protocol stayed the same, so if you make an adapter to change the connector type, you can mix and match keyboards and Amiga computers of different generations.
Amiga 2000, 3000
The Amiga 2000 and later 3000 use the same five pin DIN plug as a PC/AT or XT keyboard. But you guessed right, they aren’t compatible with each other. At least Commodore was nice enough to keep the ground and power pins consistent so you shouldn’t break anything, but I still don’t recommend you try it.
Northgate made an Amiga compatible version of one of its popular keyboards, but they are very scarce today. Adapters do exist to translate keyboard protocols so that a PC AT or PS/2 keyboard works.
The last and most powerful of the big box Amigas used a round mini DIN connector just like the PS/2 connector. But you guessed it, it’s not compatible.
It’s possible to adapt an Amiga 2000 or 3000 keyboard using the same adapter that lets a PC/AT keyboard work on a PS/2.