That is a limitation of the keyboard not PS/2. Unlike USB which is limited to 10 simultaneous key presses, PS/2 supports full n-key rollover.
This, it’s why I still use the PS2 interface. Full n-key rollover is impossible for me to do without.
Out of curiosity, what is the practical use of full N-key rollover? I can't think of many things that require me to press more than maybe five keys at a time.
Used to have these problems when we were children and playing fighting games with my brother with one keyboard or guitar hero clones that need you to press multiple buttons at the same time, that's the only use case I could think of. I don't know if there's any modern software that requires you to mash more than 2 or 3 buttons at the same time
How about a fancy IBM keyboard? The Model F from 1981 features n-key rollover. Don't ask me why they needed it at the time though. It probably wasn't important as the Model M from a couple of years later dropped that feature.
Nothing to do with the interface. If your keyboard can only do 4 it means that the manufacturer has cheaped out on diodes and couldn't even be bothered to stagger the matrix enough to make you not notice.
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I think you're confusing USB and PS/2. USB has (or used to have?) a limit on the number of keys you could press, whereas PS/2 supports n-key rollover.
Historically computers only supported punch cards, it feels weird to only focus on past capabilities. https://www.devever.net/~hl/usbnkro
I recall NKRO was the selling point on some of those keyboards, my old steel series mechanical will absolutely let you mash all the keys with a ps2 adapter.
Try playing a rhythm game on a most PS2 keyboards 😟
Also with certain button combinations it was less than 4. You could only hold 2 arrow keys down at a time.
USB: Many designs and revisions, none of them perfect
Nah, USB 3.2 Gen 2x2 SuperSpeed is the best! And it took me only 30 minutes of reading articles and wiki pages to get that information! ^although^ ^I’m^ ^not^ ^sure^ ^what^ ^USB4^ ^Gen^ ^3×1^ ^is,^ ^but^ ^it’s^ ^only^ ^x1^ ^so^ ^can’t^ ^be^ ^that^ ^good,^ ^right?^
although I’m not sure what USB4 Gen 3×1 is, but it’s only x1 so can’t be that good, right?
It's the initialisation mode of USB 40Gbps, luckily not something users will have to deal with
I know this is a shitpost, but what's interesting is that even though USB doesn't directly interrupt the CPU it's still faster. USB is able to get the entire packet sent before PS2 even sends one. It's very interesting. So if you ever see anyone unironically saying there is less latency call them out!
Are PS/2 ports still operating on hardware interrupts these days? I would expect these to be emulated as USB devices at this point, depending on whatever I/O chipset is in play.
The bit about USB asking the CPU is kinda true? My understanding is that it's a packet protocol of sorts, so it's really just writing post-it notes for each button press and leaves them on the CPU's whiteboard for later.
Yes, it's true the the USB protocol has to "wait" but it gets the message sent so much faster that it doesn't matter. Still interesting stuff though!
I recently bought a motherboard with a N100 processor, that had two 3.0 USB Ports, two 3.1 USB Ports, an HDMI and a DisplayPort. Because of that I was surprised to learn that it had also two PS/2 ports for a keyboard and a mouse.
My mechanical keyboard came with a USB-to-PS/2 adapter, and I use that instead of the USB one. Feels good
Same as VGA, shit just works, don’t need to worry about drivers or OS. So if your server shits the bed, you don’t need to worry about these things not working so you can can figure what went wrong.
Ok but Vega is still standard for servers, because you don't have to use proprietary bullshit like HDMI.
Why? Nobody needs high definition from a server. Vega is literally unbreakable, super reliable and cost efficient. Display port would be a absolute waste just like HDMI. Same with most hardware applications that don't need high definition displays. The server ports are literally only used to set up the server.
This isn't just a royalties issue, its a issue of necessity.
IDK man, it would be great if my crash cart or KVM only needed one cable. I can’t wait for USB-C on servers to be everywhere
USB-C on servers is a good thing. But you seriously don't need a HD capable port on a server.
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There is really no reason not too though. Displayport also takes up less space that would be used for cooling or whatever.
The only reason other than compatibility is probably that the screws are nice to have if you hook it up to something permanently like a KVM. Displayport have latches but imo they suck and I usually buy cables without them.
VGA is flaky and prone to issues. It doesn't have a way of reliability relaying information such as display metadata.
Everything in the world is hdmi or DisplayPort. VGA is essentially now a specialty connector used only in data centers.
HDMI has their fees, but DisplayPort doesn’t. Plus at this point implementing analog to digital converters is probably more expensive than just putting DP on it.
I don’t know what server you’re running, but I have never had any issues with USB keyboards. They just work, including in the firmware. No drivers needed. Besides, a proper server motherboard will have IPMI so you can just remote into it.
I've had KVMs that don't like the 'fancier' USB keyboards with NKRO. It would work, but it wouldn't listen for its own 'switch to different console' hotkeys. Reconfiguring the keyboard to run in 6KRO-only mode addressed it, but not every keyboard can be configured that way.
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In a server environment it's perfect. Have multiple baremetal servers in the rack?
No problem, all you need is a PS/2 + VGA KVM and you can control them easily without fiddling. No protocol handshake, no HDCP in the way.
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PS/2?
I'm not completely sure but I'm pretty sure that at least the majority of our servers only have USB and no PS/2 port. And while our servers aren't very old some of them still have a few years on them.
For most workflows, especially text, 720p is more than enough.
That said, DisplayPort >>>>> HDMI
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You've just gotta dig out the mouse/keyboard combo that came with the Packard Bell you bought in 1996 from some dusty box in the attic / storage room at work
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If there is a fault in the PS2 device it literally breaks the rest of the computer.
A little more than 15 years ago I had to fix my PS2 keyboard because it crashed everything. Not even a BSOD, just colors.
looks nervously at my 3070ti and ibm model m haha so was there any permanent damage or like
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No. It was when I was younger and I smacked the keyboard at some point. The whole computer crashed with random pixels all over the screen. I tried rebooting many times. I came to the conclusion the cable inside of the keyboard must have been slightly disconnected and pushed it further back into it, and my PC worked again.
Computers are really resilient to permanent damage to be honest. I once dropped a screw into a running computer and it short-circuited with sparks and all. I was still able to boot it, but it was extremely slow. After a few reboots it was back to normal.
Likely tripped some PTC "fuses". Often, with time to cool, they'll mostly return to normal.
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Your story reminded me of when I set my pc on fire!
No idea how or what happened but the PSU shot sparks, lit up and tried setting the house on fire. Amazingly everything worked right after replacing the PSU, but the Mobo was the next thing to blow up.
So while they are indeed resilient af, you're likely not coming out unscathed if sparks fly.
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PSUs aren't too hard to fix by yourself if you know your electronics.
Except maybe that one PSU I got for free that had safety stuff bypassed.
But yeah, a fire might be a pushing the limits.
If there is a fault in the PS2 device it literally breaks the rest of the computer.
That must be OS dependent
I think it's because PS2 has very low level support. It'd have to be pretty borked, and there's not too much to bork, so pretty rare.
My keyboard uses PS/2 and although I do have a PS/2 to USB adapter, i prefer using my computers PS/2 port because it means one more USB port can be used for something else.
30+ years old and it runs flawlessly.
Isn't almost any keyboard able to last that long?
I make sure any motherboard I buy has at least 8 USB ports, so I know I'll have enough. It does make sense to use the PS/2 port if you have the peripherals. What advantage does USB have over it anyway?
I go through a cheap Logitech keyboard just about once every three years. I replace them when a a couple of keys stop working or when the nubs wear off of the center keys and can no longer blindly find where my hands go.
Isn’t almost any keyboard able to last that long?
In theory, yes. In reality... not so much. Bluetooth keyboards are a joke for longevity, and a lot of wired keyboards these days just have piss poor build quality.
I don't think PS/2 inherently has major advantages over USB but as someone who uses a small PC with few USB ports, I appreciate having a PS/2 port available.
I had a Razer Blackwidow keyboard, lasted only like 6 years before the switches started dying. Or it got into a cult. Sometimes pressing k would type out kkk.
Usb keyboards can have n-key rollover which let's you press more buttons simultaneously, whereas PS2 has a hard limit of like 5 or so
Refer to below comment
It's actually the other way around. Check out Ben Eater's awesome videos for technical details.
TLDR: PS/2 sends separate key up and key down events, sequentially - like #1 Down - #2 Down - #1 Up - #2 Up - each in separate message, allowing for theoretically infinite rollover (excluding certain edge-cases). USB, on the other hand, polls only for keys being pressed at the moment. By default, the keyboard responds with a 8-byte message, with 1 byte being the bitmask for 8 modifier keys (4 on each side), a spacer, and 6 bytes/slots for identifiers of keys being held down. If one identifier is present in one response but is missing or replaced in next one, the system assumes a key-up event. It is possible by USB spec to negotiate connection in such a way that the keyboard responds with a bitmask for every single key it has. But this is not well supported by things like BIOS and KVM's, so very few keyboard manufacturers bother implementing it. Most keyboarrds advertising NKRO are actually only capable of doing so via the PS/2 adapter.
I've often thought this about older or less generally useful ports, but then it just keeps coming back to the fact that, if I had the same number of spare ports, plus one more USB that I useD for this keyboard instead of a dedicated PS2 or an old USB 2, I'd be in the same situation but with at least one more useful and fast USB that maybe I might for some reason want to use without my wired keyboard plugged in.
It makes sense in terms of cost, because the older more narrowly useful port is hopefully cheaper, but otherwise it's just unnecessary and more limiting than the same overall number of ports where all of them are the most widely useful and fastest possible throughput.
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I actually use a keyboard with that connector with a converter ( to USB ). It works pretty well.
Fyi, I’m using a very old happy hacking keyboard my father gave me
Here’s the picture of the keyboard I found on the Internet:
Model-M from 1992 checking in, with all its PS/2 to USB adapter glory. Works great, and is heavy enough for home defense, removing unwanted fingerprints from walls, and smashing produce.
Control in the right place! I always have to use registry hacks to get caps lock to be Control in Windows.
Hahaa.. laughed at this, checked my computer only to see my keyboard is using this... It didn't at all bothered me all these years, so.. Long live
I'm glad to have it. I have to keep my old PS/2 keyboard plugged into that slot so I can get into the BIOS. My USB keyboard isn't recognized until it's too late to interrupt the boot process.
I had the same problem until I learned motherboards tend to prioritize the top usb slots or specific ones for the boot process. Switching to those fixed it for me. Any such luck?
I did try that but unfortunately it didn't work on my system. There is also an option for the systemctl reboot command that I haven't tried yet but plan to next time I need to get into the BIOS. IIRC it's --firmware-setup. It's supposed to reboot you into the BIOS, but whether it works or not depends on if your hardware supports it.
I had to mess with an old laptop the other month, and the built in keyboard didn't activate until after the deadline for getting into the BIOS.
But plug in a USB keyboard, and away it goes.
Like, who designs this shit?
We asked our Dell sales guy this question years ago now, when they had been removed one year and quickly added back the next year.
They are there mostly for government builds, and other places with high security requirements. Usually the requirement is that they need to prevent any unauthorized USB devices from being plugged in. With the PS2 m&k ports they can disable the USB ports entirely in the BIOS.
That makes sense! The convenience of USB means that this single point of entry is now a critical security risk.
So you want to connect your mouse and keyboard, but all your usb slots are taken? I got your back, fam!
Not necessarily, modern having keyboards can operate at upwards of 1khz polling speed. The main difference is, that usb needs polling in the first place, whereas ps/2 is interrupt based.
That essentially means that ps/2 tells the computer "hey a key was just pressed" instantly and usb waits to be asked whether a key was pressed or not. If the latter is done often enough the difference becomes negligible.
Higher than that, I have a keyboard with 8000hz polling and a mouse with 4000hz polling. Anything over maybe 2k at most is hard to perceive, at least for me
I think a high polling rate matters more with N-key rollover (lots of successive keypress messages in one bunch), which in turn matters for some gaming scenarios.
but the protocol is slow. with high speed usb and fast polling rates, even though ps/2 starts sending instantly, usb will often have had time to poll and send its whole packet before ps/2 has finished sending.
Not necessarily. Even though PS/2 operates with a superior protocol, latency-wise, the clock speed is atrocious, resulting in an effective polling rate of about 1500hz, give or take. We could account that it doesn't need to wait for request to send keystrokes like USB keyboard do, effectively doubling it even more, but then we'd have to account for whatever delay Super I/O chips introduce and I'm not qualified to talk about that. But, if your keyboard is not from a dollar store shelf then it probably runs on at least 1000hz, at which point we are talking about sub-millisecond differences which would be quite hard to notice. 4000hz keyboard definitely beats PS/2 though.
Went to Disney recently and had a lot of time to wait in line. I found a ton of old tech recycled into decorations in their Star Wars area. I got to explain circuits, hard disks, and old connectors to my kids.
NGL I literally still use a PS/2 port for my decent yet extremely old membrane keyboard from circa 2007.
I meant to upgrade to a customized mechanical keeb a few years back, got a bunch of sample key caps and switches, got really overwhelmed by the choices, and never bought anything permanent.
In my dream scenario this choice pays off when some fed agency tries to install a hardware keylogger and can't because I'm the last idiot still using a PS/2 keyboard in 2024.
I'm currently using a PS/2 Dell AT101W while I procrastinate fixing my AT Leading Edge DC-2214