In the 1990s most IBM-compatible computers had a couple of PS/2 ports, one for the keyboard and one for a mouse or other pointing device. These were supplanted by USB connectors, which are used not only by keyboards and mice but pretty much every other kind of peripheral you can think of.
Back in the day, was the PS/2 connector ever used for consumer peripherals other than human interface devices (keyboards, mice, joysticks, trackballs, and the like)?
The PS/2 connectors are basically the original IBM PC keyboard connector electrically, just shrunk down a bit for the IBM PS/2. Back in the day, you could get adapters to convert between the two different sized connectors. The connectors were originally driven by a microcontroller on the motherboard which was dedicated to keyboard and mouse functions. It was not a generic port and did not have any kind of generic driver for it, which would have made it difficult to connect something to it that wasn’t a keyboard or mouse or some sort of human interface that functioned similarly to one of those. If you wanted something else, that’s what the serial and parallel ports were for.
KVM switches usually got their power from the PS/2 port and also often monitored the keyboard for the command to switch. Other types just had a switch or button on the KVM switch and didn’t monitor the keyboard, and some had both keyboard commands and a manual switch…
There were a few oddball things back in the day that plugged into the PS/2 port (or the old XT/AT style keyboard port) just to get power from that port. You would then plug your keyboard into the device’s plug so that your keyboard still worked. Actual communication to the device would usually be through the serial or parallel port. These types of things weren’t common. I remember a prom programmer and a modem that got their power that way.
The connector itself is a mini DIN variant which is used in other applications. You may remember S-video cables. We sell an instrument at work that uses miniDIN for a serial connection to a label printer.
We still use them in the warehouse. It’s a nice wireless rugged scanner in a keyboard wedge application for data collection from a browser to cloud storage. Eventually, we’ll have to replace it but only because the batteries are getting scarce.
Even more clever (although a feature of the scanner units, not the PS/2 interface, so a bit off topic) - many keyboard wedge barcode scanners are configured (for switching on/off options like ‘emulate the return key at the end of a scan’) by scanning one of a set of control barcodes that were supplied in a booklet with the device.
It sounds obvious, but it’s a lovely design idea - recursively use the function of the machine to configure the machine.
The as mentioned barcode scanners are about it.
the ports only deal with certain data types.
Most desktops, the ports are dedicate keyboard or mouse, not both.
The keyboard port is only looking for keyscan codes.
The barcode scanners work, because they transmit keyscan codes, basically act like they are typing.
The mouse port only looks for mouse data packets, which consist of axis input for X Y and Z, and bit states for the buttons, i think 5 was the max with intellimouse drivers.
The standard with no special drivers is just X and Y axis and 3 bit states for buttons.
The only thing i ever saw plugged into them were some robotic controllers, which were really just glorified mice in the form of a joystick.
Some laptops have/had auto sensing PS/2 ports where they would sense if it was mouse or keyboard and switch accordingly, could be some desktops also.
Those kinds usually have only 1 PS/2 port.
The data the port can deal with, as you can see, is too limited in nature to do anything cool like take scanner input etc.
Serial and parallel ports got the cool stuff, printers scanner modems even game controllers and lots of commercial stuff.
Now, usb does everything, wish it did back then, i still have tons of various cables and adapters for hooking stuff up to serial ports
At the time, most systems still had serial ports, which were more flexible and better understood by electronics/computer engineers. So I’d wager that most niche or oddball devices used serial for familiarity, ease and avoiding the newfangled one-off non-standard port.
Lots of things still do this. It makes them very easy to use with existing applications. Just rooting around what’s in my drawer now, I’ve got a laser pointer presentation thing (you know, for PowerPoint) that simply sends PgUp and PgDn, and a digital vernier caliper that sends numerals, decimals, and newlines (great for capturing data into Excel or NotePad++). These are both USB (well, the pointer uses a dongle).
I thought PS/2 had died out but in a recent issue of PC Gamer magazine they review some of the latest motherboards and 4 out of the 7 reviewed have one. The port is coloured half blue and half green to show (I guess?) that it supports either mouse or keyboard. Are there still PS/2 mice and keyboards being produced?
They’re certainly still being sold as new products. Go to any online electronics retailer, such as Amazon, and search for “PS/2 keyboard”. You’ll get plenty of hits. I suppose this means that they’re still being manufactured.
PS/2 mice are obsolete (though may still be produced), but PS/2 has advantages for keyboards. It supports NKRO (n-key rollover), that is registering an unlimited number of keys pressed at one time, has lower latency than USB, and since it’s on a single port instead of a bus can’t have congestion issues with other devices. Realistically I’m not sure if you’ll ever hit the limits in practice and the only people I can think of that care about this are hardcore gamers, but hardcore gamers are a major customer group for high-end keyboards and non-assembled motherboards, so I don’t think you’ll see PS/2 go away anytime soon.