Why do Modern Motherboards Still Have PS/2 COnnectors?

[DemonDragonJ]

I have noticed that many modern motherboards still have PS/2 connectors, despite that connector being outdated. Why is this? USB offers faster data transmission than does PS/2 and is has plug-and-play functionality, which PS/2 does not. I know that PS/2 connectors are used for mice or keyboards, but most mice and keyboards use USB as their primary connector today, and since most motherboards have as many as eight or ten USB ports (with the ability to add more via the use of add-on cards or front panels of the case), I cannot imagine that using two USB ports for the mouse and keyboard would lead to a shortage of USB ports.

What does everyone else have to say on this subject? Why do modern motherboards still have PS/2 ports?

[xr4man]

i agree.

however, i have found on my msi motherboard for my htpc, if you are connected witha usb keyboard and try and get into the bios, it will stop working. or in otherwords, you can get into the bios, but then the keyboard stops. a ps/2 keyboard works perfectly though. so, my guess would be for lazily programmed bios's that don't work with usb keyboards.

i would also like to point out that my asus, biostar, foxconn, and jetway boards all work just fine in the bios with a usb keyboard.

[Aldersan]

No clue, maybe because there are still advantages using ps/2 connectors for something? I don't know anyone who does, but I know that there are advantages to ps/2 such as it has infinite key rollover, which USB is strictly limited in, but who knows.

[diluzio91]

usb does not support N key rollover, while PS2 does.

[Airbozo]

There are also a lot of ps2 based KVM systems out there still in use. From the servers I build, I see both. About 80% of the servers that pass through my hands have PS2, the rest don't. That was a shock to one of my customers and they had to buy some special adapters to be able to use their KVM.

[nevermind1534]

My keyboard is PS/2 (it's an IBM Model M)

Also, although it's not enough to even notice or make a difference when it happens, since USB is a shared bus, everything plugged in is using it and sharing bandwidth. The keyboard isn't given priority over everything else, so there can be lag (not enough to even notice, but there it's still lag).

[Drum Thumper]

Two words: Backwards Compatibility.

Similar to how USB 3.0 ports can take 2.0 devices.

[billygoat333]

I am currently using a ps/2 mouse and keyboard on my i7 rig... and a wireless keyboard mouse combo as well. lol I use the wired controls for my desk and I leave the mouse and keyboard on my bed for media purposes. It works well.

[DemonDragonJ]

usb does not support N key rollover, while PS2 does.

Why would a newer technology not have a feature that an older technology possesses? That makes no sense to me.

[Aldersan]

It has to do with how USB keyboards and ps/2 keyboards send their data, see http://goo.gl/3euRf , hope I'm not breaking any rules by linking to other forums :P

[AmEv]

You're not (around here at least). As long as you're not blatantly advertising them specifically, you should be fine. Sometimes, another forum has the answer.

[Kayin]

PS/2 is far superior, and uses less resources. USB was simply an attempt to get everyone on a shared bus, even if it sacrificed features.

Most of the top OCers use PS/2 peripherals,and they have the money to go with newer. Should look up polling rates, interesting stuff about how each works.

[DemonDragonJ]

PS/2 is far superior, and uses less resources. USB was simply an attempt to get everyone on a shared bus, even if it sacrificed features.

Most of the top OCers use PS/2 peripherals,and they have the money to go with newer. Should look up polling rates, interesting stuff about how each works.

PS/2 is not hot-swappable, and the pins on the connector are exposed to damage, unlike the embedded pins of a USB connector. If what you are saying is true, what would be a good solution to this situation? How can USB be improved to "use less resources," as you say, while still maintaining the features that make it so appealing? Plus, how much system resources could a mouse and keyboard possibly consume, especially in comparison to graphically-intense games or the playing of high-definition movies and music files?

[Aldersan]

From my understanding, USB is constantly being polled by the computer, which does use up some (however small) resources, whereas ps/2 is only sending data when a button is pressed. In order to fix the N key rollover issue, it seems like they would have to come up with custom drivers or firmware or something instead of the usual, to fix the issue. I guess they're just more interested in sticking with the normal, tried-and-true methods, and motherboards keep ps/2 for those who want it.

[Kayin]

Demon, every little bit counts when what you're doing involves strapping an LN2 pot to it. Benchmarking is a place USB simply isn't found, and since I still do it, that's what I'm using. Most good mechanicals don't come in USB either, and those that do don't support n-key rollover.

[Aldersan]

I've got the razer blackwidow ultimate :D pricey, yes but i love the backlighting and the mechanical keys are amazing, it's USB and while its made for gaming (certain keys have higher priority so that the 6 key rollover isn't as big of an issue), i could certainly go for n key rollover by ps/2 :D

[NightrainSrt4]

I still use a PS/2 keyboard. Sometimes I still have a need for parallel/serial ports too.

The way I look at it, if keeping the ports doesn't hamper performance of the board, and there is space on the back of the board, then boards should keep them. I don't need 12 rear panel USB ports. I don't have enough bandwidth starved devices that I would need that many ports, assuming each really had its own controller in the first place. People seem to forget each controller can support daisy chaining of up to 127 devices.

Variety is the spice of life. But the market segment that buys the same kind of boards I do just want to plug in a bunch of graphics cards and go play games, so what need would there be for ports besides USB, audio, and lan? The other ports look too ugly to be on the back of the case where no one can see it.

[AmEv]

I have rarely used FIVE USB. I don't need a board with 20 rear-panel USB.

[SXRguyinMA]

I'm currently using 10 USB's - KB, mouse, headphones, external HDD, flash drive, camera, 2 dev boards (Arduino and ChipKIT), wireless adapter and the ipod dock. Granted I never use them all at the same time, but it's nice to have them all already plugged in so whenever I want/need them I just hook the cable to my device and I'm good to go

[NightrainSrt4]

A hub would allow the same thing and you wouldn't need to lose variety in ports. If a group of devices don't need power they even make them in splitter type cables, so you can plug it into the back of the case as usual, and plug the devices into the hub/splitter.

[Kayin]

Why in the name of Bill Gates' furry man-ovaries are your headphones USB? You know that bypasses your onboard sound, right?

[diluzio91]

i was just thinking that i have 14 usb 2.0 ports between my case and mobo... and only 2 usb 3.... =?

[AmEv]

Very few devices are USB3. It's only a few months old. Which is why the max amount of USB3 board on a mobo is four. Need more, add-in card is currently the only way to go.

[Twigsoffury]

Didn't see it mentioned here, but ps2 cables can be long....very long....very very long. while USB is limited to about a little under 20 feet or something like that.

[AmEv]

Without some sort of hub/extender:
USB 1.1: 10 feet
USB 2.0: 16 feet
USB 3.0: ?? feet

[nevermind1534]

Why in the name of Bill Gates' furry man-ovaries are your headphones USB? You know that bypasses your onboard sound, right?

My headset is USB. The sound quality is much better than the onboard Realtek HD Audio, and the sound quality will be the same on any computer (It's the Creative Fatal1ty headset).

When I do eventually get a decent sound card, I'll get regular non-USB headphones to use with my computer. I'll probably still use the USB with my laptop and most other computers, though.

[Twigsoffury]

My headset is USB. The sound quality is much better than the onboard Realtek HD Audio, and the sound quality will be the same on any computer (It's the Creative Fatal1ty headset).

When I do eventually get a decent sound card, I'll get regular non-USB headphones to use with my computer. I'll probably still use the USB with my laptop and most other computers, though.

Don't forget there is a limit to the number of sounds a device can render at once.

most of them USB headsets are 16 sounds, with a few being 24.

Realtek HD is 32 sounds/ standard realtek is 16. and VIA being 8 (lol)

Most creative cards handle 64 voices, the X-fi's and my azuentec handle 128 voices.



Lemme tell you there is a HUGE HUGE difference between 16 voices and 128 voices.


Did you know you can hear the rain on GTA all the time, not just when your walking?

i never knew that until i installed the azuentec card and the audio of the rain wasn't cut off by people talking, walking, the car engine, skids radio and effects.....from the 24 voice limit

[AmEv]

Creative.... SBLive...

Now I want another one.

[Kayin]

I might have one in a box unused. I have to do some sorting, if I've got it I'll set it aside. Does me no good.

[Konrad]

PS/2 is not hot-swappable, and the pins on the connector are exposed to damage, unlike the embedded pins of a USB connector. If what you are saying is true, what would be a good solution to this situation? How can USB be improved to "use less resources," as you say, while still maintaining the features that make it so appealing? Plus, how much system resources could a mouse and keyboard possibly consume, especially in comparison to graphically-intense games or the playing of high-definition movies and music files?

I don't know many people who hot swap keyboards. In fact, my experience is that interface devices (specifically keyboard and mouse) sometimes work poorly and require some OS massaging or even a reboot when hotswapped, regardless whether or not they're USB.

True, USB cable connectors are physically superior ... they still can and still do break, though seemingly less often then PS/2 pins did. My anecdotal experience, however, is that USB ports themselves break far more often than PS/2 ports do - although it's possible that's just a symptom of modern industrial corner-cutting or a greater number of clumsy idiot users stubbornly forcing the connectors on "backwards". I've only seen a few mobos with broken PS/2 ports, but I've seen a great many with some broken/nonfunctional USB ports.

PS/2 always runs some kind of hardwired 8042 emulator on the (slow) "Southbridge" or "Super I/O" chipset component. USB HID services also run on the same 8042 circuitry (or on some other chip for add-on USB hubs/controllers), after enumerating and translating data through a variety of USB logic ... in theory this means that it is at best the same speed (though more likely it is slower) and automatically uses more power and circuits and mobo resources than the straight PS/2 counterpart.

Performance ... more USB functions plugged into more USB controllers means more power and more processing, the computer is busier. True, a keyboard and mouse (or even the usual pile of common USB gizmos) is fairly trivial in terms of raw number crunching and wattage ... but it all adds up, and on USB it's all dividing resources (clocks, power, bandwidth) somewhere on the mobo, no matter how cleverly things are designed. PS/2 has fixed protocol/bandwidth/power allocations, it is constant while USB busses fluctuate. A fancy gaming keyboard might advertise incredibly "fast" USB polling, which means nothing because the polling is still bottlenecked by 8042 compatibility - and by software (USB HID libraries, OS, etc). Bandwidth on PS/2 devices does not "stutter" and "burst" and get interrupted by varying loads on a shared bus, and they do not fail when other devices on the shared bus crash or lock up.

PS/2 supports true unlimited NKRO, although functionally limited to about 8KRO and ~112.25wpm max typing speed in practice (and likely much less on today's cheapass keyboards). USB is designed to support a maximum of 6KRO (although, again, this really doesn't matter much these days).

Final point for PS/2 ... no matter how wonky and screwy and busted up and cantankerous a computer might be, no matter how fried the USB services might be, even if it's at the chipset-level, the PS/2 is so deeply embedded and hardwired that you can almost always access the BIOS with a PS/2 keyboard when no USB keyboard can possibly work. If nothing else, it's at least another layer of redundancy for "bare bones" system repair.

Of course, having said all that ... a USB keyboard or mouse can provide additional functions above and beyond the basics; anything digital is possible, assuming it can be computed on 100-500mA or less. In reality this means nothing, it's basically just piggybacking multiple USB devices (such as, say, a slaved USB controller hub, an audio chipset, a little BT transceiver, or a LCD screen) within a single keyboard/mouse component. PS/2 cannot do any of this stuff, of course. Personally, I prefer to keep my hardware inside the main PC chassis plugged into proper slots on the mobo, where it belongs and where it will offer maximum performance and capability ... but at the same time, sometimes the convenience or bling or "coolness" of stuff integrated in the keyboard/mouse is nice to have.

If your PS/2 is just too offensive then plug in one of those PS/2-to-USB "keyboard" adapter thingies and use it as a constant 5V power source for recharging USB devices.

[DemonDragonJ]

Wow, another user revived this thread after more than an entire year had passed since its previous post: that is most impressive.

So, Konrad, shall I presume that you favor PS/2 over USB, and that you believe that PS/2 shall not be obsolete at any point in the near future? If you believe that, then I have another question: what potential does the PS/2 interface have to grow and improve? USB can continue to improve with each new version, but I have not noticed any revisions or upgrades to the PS/2 interface in some time, which suggests that it does not have any room for upgrading.

[Konrad]

I'll admit that PS/2 spec was never designed to be scalar, never designed to accept any other devices. It's really just another PC/AT component which worked so well it became the de-facto industry standard for many years. I don't even think any official documentation was ever published, although the tech is comparatively simple to figure out.

USB standards involve all sorts of compliance testing, engineering, and extensive intercompatibility testing, where even the most trivial details merit very serious consideration. All governed by a central "non-profit" sort of corporation which does a pretty good job of ensuring conformity and compliance. A vast number of el-cheapo USB products do exist, at least products with USB plugs which generally work well enough, but a careful observer will note the conspicuous lack of proper USB branding on these products.

The reason PS/2 is still integrated in PCs is legacy compatibility. PS/2-capable keyboards and mice are still being sold (although many are actually USB devices with some kind of internal PS/2 emulation or compatibility mode). Certainly, we are at (or soon will be at) the point where PS/2 connectors disappear from laptops and other devices, but I'm willing to bet they'll remain standard issue on desktop mobos for many years. Legacy junk may not be fancy, but it's widely available, dirt cheap, and basically always works even when the latest-greatest fancy new tech fails - and again, basic user interfaces (keyboard, mouse) are sort of critical requirements for fixing everything else, including added functionality on the basic user interfaces.

Microcontroller guys and modders/hackers/etc have developed all sorts of clever uses for PS/2 parts. Of course it would be foolish to expect major PC engineering/marketing to accommodate our puny minority if they ever decide to chop PS/2, and we're always able to modify or construct our own PS/2 interfaces when none are provided.

For the record, I deliberately chose PS/2 protocol on my "perfect" gaming keyboard, it is more responsive and more capable than USB/HID allows (I considered using a COM port approach for instant-response full NKRO, but decided I can tolerate PS/2 limitations instead, lol). But at the same time, my keyboard cable is actually a bundle with pass-through USB and audio functions, since it's just really convenient to have these functions on my keyboard ... and I also use a second keyboard (USB) for general typing/programming stuff. My uber gaming mouse and regular cheapo mouse are both USB, since PS/2 response is clearly inferior in this regard ... and the only pure PS/2 mouse I still own is an ugly biege ancient ball-mouse thingy without a scrollwheel.

The reality is that the keyboard limitations designed into USB spec already exceed anything most users will ever need or notice, unless perhaps doing some frantically extreme multikey-mashing gaming. I would expect that if it was ever perceived by the market/industry as a "serious" limitation then a faster HID standard would be officially engineered on subsequent USB specs (I think this will eventually really happen, but only when all USB keyboards force the need with ridiculously extensive features and macros and such) ... but we will not see any further changes in PS/2 spec.

Sorry about the thread necro (and walls of text haha). I think I fell for the spammer again.

[TLHarrell]

Konrad, all your posts are a huge wall of text. Of course, it's relevant and I always consider it a good read. You either have a massive electronics encyclopedia you're copy/pasting from, or you've got some serious EE chops.

I actually found it rather hilarious that when I built my current desktop system I needed a PS/2 keyboard to get into BIOS (simply because it wouldn't enable USB prior to BIOS entry in the boot cycle), as well and a floppy drive (to install RAID drivers). Of course, I keep the PS/2 keyboard around for when I occasionally work on PCs for others as it always works. Most of the time they only bring the box anyway.

[Konrad]

I think self-educated hobbyist/amateur EE people often know more (irrelevant details) about the topic than properly educated EEs. Avocational passion rather than just a plodding vocational money path.

[TLHarrell]

I have a very good understanding of a great many things, electronics included. But my knowledge is not as encyclopedic as yours seems to be. Certainly paves the way for more time spent fooling around with stuff, less time spent looking for the correct information and getting calculations right.

You should certainly look into gracing us with some EE type articles. The site could always use some content, especially good, relevant and exclusive content.

[Konrad]

This particular specific topic is one I just happen to know a great deal about after building my own "perfect" keyboard controller. lol, I wouldn't participate in discussions about topics I don't know anything about.

[Xpirate]

I actually found it rather hilarious that when I built my current desktop system I needed a PS/2 keyboard to get into BIOS

This is the reason why I still have at least one PS/2 keyboard in my small repository of computer junk.

[Konrad]

I've actually "retromodded" USB keyboards to PS/2. Real PS/2, with the old scansets and controller interfaces, not the hybrid (USB native, PS/2 emulated) types which have been standard issue for at least a decade.

I constantly need these keyboards to interface with non-PC platforms. Older peripheral tech seems to dominate industrial control panels and such. Sometimes (though with diminishing frequency), my microcontroller projects need a quick keyboard interface but don't merit the effort and complexity of integrating USB libraries.

[Azrael5]

Simple, because PS/2 connectors are better than USB for resources consumption and time responsivity, and simultaneously keys typing.

So PS/2 motherobards are better than without this conncetors.

REasons why PS/2 is preferred to USB:

1) PS/2 is hardware interrupt-based, while USB port is polling-based. When you press a key on a PS2 keyboard, it generates a hardware interrupt immediately, while USB polls your keyboard many times per second (125 Hz by default, up to 1,000 Hz in "gaming" keyboards) to see if any keys a pressed. This means that PS2 keyboards will have the lowest latency - although in all likelihood, you will never notice a difference. Perhaps more importantly, polling is more CPU-intensive, especially if high polling rate (like 1,000 Hz) is used.

2) PS2 supports full n-key rollover. USB keyboards are generally limited to 6KRO (able to recognize up to six simultaneous keystrokes). Of course, it also depends on the keyboard: most cheap keyboards are just 2KRO, and it does not matter whether you connect such a peripheral via USB or PS2 port: it will still register only 2 keys at once. Full NKRO is a feature usually found in gaming keyboards.

3) PS2 keyboards are more compatible with older hardware and software, which might be important for some users. To be perfectly fair though, turning on "Legacy USB" in BIOS means your USB keyboard will work in those cases as well, which almost makes this a moot point.

So Ps/2 input devices get a excellent latency in confront of USB.

[Konrad]

1) USB polling is based more on bandwidth than timing. ~125Hz is a fair assumption, but ~1000Hz is - at best - a marketing department's unrealistically optimistic spin of "the best case scenario" on an otherwise unoccupied USB bus caught in an unlikely series of moments of perfect timing. Keyboards advertising "1KHz" - even if/when they live up to this spec - are not realistically polled any faster than "slow" USB keyboards, and may in fact perform quite poorly (vs their PS/2 counterparts) when sharing a bus crowded by many USB devices (or even if caught sharing with just a single USB device which rudely hogs the bus).

2) PS/2 "full" NKRO is functionally limited to 8KRO, or even less on the vast majority of 8051 (compatible/emulated) keyboard controller parts. There's an "8051" in every keyboard and (somewhere in the SuperI/O chip) on every PC/AT-compatible mobo, and the slower one bottlenecks actual keyboard throughput. Kind of a moot point on most keyboards anyhow, since engineering tradeoffs and cheapest-possible matrix layouts means they're functionally limited to usually 2KRO or 3KRO (even the higher-end gaming keyboards which advertise "anti-ghosting" and such stuff are usually just cheapy 2-3KRO circuitry with WASD-optimized clusters). Another limitation imposed on PS/2 NKRO bandwidth is the theoretical limit of 112.5wpm max typing speed, while no actual limit is (theoretically) imposed by USB specs - although, again, the same cheap keyboards/parts/thinking would probably dictate much lower thresholds.

The wiki at geekhack.org is pretty definitive, although I personally find the forum leaders and their "keyboard science" are really more like stuffy "keyboard dogma". Still, if ye can't say anything nice ... then come to TBCS!