Not sure about the technical details and price comparisons, but I believe the reason is simply that USB was developed spesifically to replace all existing peripheral connectors - and as such PS/2 goes the way of the COM-ports.
THe industry decided to adopt one standard - and therefore it makes no sense to keep the old connectors anymore.
that USB is universal (that’s what the U stands for) which means that all external appliances will fit onto all computers.
and
that USB is faster than other plugs that basically have the task of transferring info from outside the computer (be it from a digital camera, a mouse, an external hard drive or a keyboard) into the computer.
There’s really no benefit that I can see to having different kinds of peripherals plug into different ports. If the problem is that your computer doesn’t have enough USB ports, the solution would be for the computer manufacturer to give you more USB ports, not to give a whole bunch of specialized ports.
I’d argue that’s some of the benefit of everything going to USB. Instead of your computer’s manufacturer having to guess how many you want of each kind of peripheral, they just have to guess the maximum total number of peripherals you’re likely to have.
Economies of scale, I’m pretty sure: It’s cheaper to make and to buy a ton of USB hardware than smaller amounts of specialized connectors.
Also, software makers like it because all of a sudden a lot of their peripheral code is reduced to a small, well-tested piece of USB-handling code plus a little extra, as opposed to having specialized code to handle each kind of connector with much less usable overlap.
Finally, it’s easier on people putting computers together. USB connectors can’t be plugged in backwards, upside-down, or into the wrong port. They’re all completely compatible and they’re even hot-swappable (you can add and remove USB devices while the computer is running). And, if you don’t have enough, a USB hub is relatively cheap.
The AT connector replaced the original IBM PC/XT connector. The signals were basically the same. The AT keyboard just had a few more keys.
PS/2 just shrank the connectors so they weren’t so big and clunky. From an electrical and software point of view, nothing changed.
Electrically, the AT (PS/2) standard is clunky. It’s basically based off of the crude way that hardware was interfaced back in the 8086 days, and it consists of unbuffered TTL level lines that originally connected the microcontroller in the keyboard directly to the microcontroller on the motherboard. If you were lucky, someone put a fuse on the 5 volt supply line. Other than that, the only protection you had was whatever was built into the microcontroller’s I/O lines. Hot swapping (unplugging and plugging while under power) a PS/2 device in the early days was a guaranteed way to break something. As microcontrollers in general got a bit hardier with their I/O lines, later PS/2 keyboards and mice were less likely to fry if you hot swapped them, but it was still ever a good idea to do it.
A bunch of folks got together to decide the future of PCs. At that point, PCs had serial ports, parallel ports, keyboard and mouse ports. The goal of USB was to replace all of that with a single bus that was modern and had features like hot swap capability and a built in power supply for low power devices (500 mA). It also had a higher data rate, though it was still designed for relatively low speed devices (i.e. not disk drives). This would allow manufacturers to get rid of all of the different ports on the computer (and their associated interface chips on the motherboard), and would make things easier for the user as well, by having all of their peripherals on a single universal “network” of sorts. It was envisioned that there would be a single USB port on the computer. This would go to a hub (typically built into the monitor stand), to which all other devices would be connected.
Later USB standards upped the data rate, so that now you can even use it for disk drives and other high bandwidth devices. Folks also didn’t like the idea of an external hub so much, so multiple USB ports on the computer has become standard.
There was nothing “wrong” with PS/2. It was slow and a bit clunky, and required some dedicated hardware, but it worked. Same with serial and parallel ports. They all did their job. The idea wasn’t to replace them because they didn’t work right. The idea was to replace them all with something that worked better and was more uniform. Now you don’t need a parallel port for your printer and a serial port for your mouse and a PS/2 port for your keyboard. You just have one USB port that does it all.
And that’s an important aspect of it: you can daisy-chain hubs. SCSI already had the daisychain feature but it was not easy, cheap and universal on the PC bus. You can buy a cheap passive 4-port extender dongle for $15 at the store and under $10 online, so your keyboard, mouse, printer can all be plugged in and you still have all your original amount of ports open.
If there’s any connector I miss these days is the motherboard conventional telephone modem connector, missing from a lot of netbooks, under the presumption that you will always be within range of a functioning WiFi or Ethernet hub. OTOH conventional telephone modem and a fully charged battery = I could get e-mail out even when the mains power is out. Kinda nice to have if some weather phenomenon knocks out the power.
I understand that there may be some performance degradation if you put your flash drive into a USB hub shared with other devices. (Readyboost users take note.) I assume that external hard drives would also benefit from a direct connection.
Is there a relevant loss of performance with, say, plugging a mouse, keyboard and printer into the same hub? While I’m at it, do hubs vary in quality? Is the hub on my monitor likely superior to a $15 1:4 USB adapter?
[hijack/tangent]A PS2 to USB converter enables those with a bunch of old keyboards to a) use them if they prefer the feel of their old keyboards for ergonomic or other reasons and b) maintain backups for the nearly inevitable beverage spills. [/hijack/tangent]
Thanks to all for the replies.
They had to get rid of PS2 connectors because too many people were going berserk after spending $100 for a Playstation 2 on Ebay or Craigslist only to end up with a keyboard cable.
Incidentally, the new cheap desktop machine I bought last year came with a PS/2 mouse and keyboard. I was a bit surprised, since they don’t really sell them as stand-alones.
I guess there must still be some cost savings for PS/2 over USB.
We Mac folks never had PS/2 keyboards and whatever connector your mice used and so on. We had ADB (Apple Desktop Bus), a daisy-chaining serial protocol that supported up to 15 devices (give or take) and which was pretty cool in its day. Of course, as with your PCs, our Macs had other ports for other purposes: serial ports for printer and external modem and other devices such as MIDI controllers. (BTW, serial ports were DIN-9 on our computers, not DB-15 like YOUR serial ports, SCSI (which was Db-15 on the computers, although not remotely compatible with your serial devices, but Centronix 50 on the peripheral devices themselves…
Our ADB and serial port architectures were out of date by the time the original Bondi blue iMac made its debut. Your PS / 2 and etc architectures were even more so. (See above posts). USB handles far more bandwidth than ADB or classic serial port and, more importantly, it eliminates the need for a sprawling mass of ports. Some other ports persist (video, audio-in and audio-out, FireWire) but USB can accomodate many of those types of signals as well. (Audio equipment can often interface with USB; external hard disks can do so; etc)
Simplifying the chaos is a good thing. Faster bus speed is a good thing. Eliminating a totally different batch of ports for Mac and PCs and arriving at a common ground is a good thing.
For me the ability to hot swap and not restart the system if a keyboard cable needed to be moved or changed is a big deal. PS2 did not like that one bit.
The hot-swappable aspect of USB is really the “killer feature” in my book. It’s easy to pop a connector while fiddling with wires or adjusting the position of the case. Over the years, I’ve seen one too many motherboard sent to the great parts bin in the sky due to the simple mistake of pulling a cable out.
In the long term, replacing PS/2 with USB means that computers can stop building the SUPPORT in, which saves a few lines of code.
PS2 connectors sucked anyway. They had to be pin-aligned, and it was very hard to do visually without actually looking at the pins. Whoever thought of making the connector perfectly round was an idiot. Yes, there’s supposed to be a little alignment line, but those are often almost invisible or worn off. So most people would put their connectors in by trying to push them in, and then rotating the connector until it goes. The result is that the plastic facing of the female connector can get chewed up and the pins of the male connector can bend. Had they made the physical package just slightly different (say, oval instead of round), it would have been much easier to plug things in.
USB is much better, as there are only two possible ways it can physically go in, and it’s strongly keyed so you can tell instantly if you’re putting it in backwards.
It could be improved, though. They could have made it so that the direction didn’t matter, or made the physical shape of it such that it clearly only fit one way. But at least it’s better than Ps/2
The other reason it’s nice to have universal connectors is that manufacturers no longer have to make separate versions of their products for different computer systems. This keeps price down.
They could have. But it would have cost more. And maybe, people who aren’t smart enough to figure out how to plug it in (with only 2 possibilities, and one of them is correct) ought not to be working on a computer?
