USB KVM vs. PS/2 KVM switches

Is one of those types of KVM switches better than the other in any way?

Depends what you want to do, but for the most part they are equal. I often use a USB adapter on my PS/2 KVM switches with no problem. In most modern computers that still have PS/2 ports, the PS/2 bus is actually part of the USB bus. ---EDIT--- After doing some more research I found that the HIDs themselves are actually responsible for making the connection via USB or PS/2, not the motherboard. Please read comments.

One faster than the other?

No.

Is the switching instantaneous?

For the most part. The speed of switching has more to do with how fast your monitor reacts than anything else.

Transparency for the OS: Does the OS even know about the switch?

No.

Does it know when the switching is performed?

It may know that 'something' happened because several events will have taken place (i.e. you might have pressed keys on your keyboard to make the switch happen, the monitor connection might have been lost due to the switching, ect.), but it does not know that the events were caused by the KVM switch.

Is it just like plugging and unplugging the devices?

Yes and no. The result is just like unplugging and plugging in the devices, but without the side effects (for instance your computer will not have to recognize your USB keyboard again when you use a KVM switch, but it probably will if you unplug your keyboard then plug it back in). Hotswapping PS/2 connectors is not recommended because it can cause I/O controller damage.

(if it is, then switching PS/2 is clearly faster than USB) Or it's a more elaborated signal handling?

It is more than signal handling, it is magic.

---EDIT---

The first picture below is my primary KVM switch. I have a wireless keyboard and mouse combo attached to it. The wireless adapter has both a USB (for keyboard) and PS/2 connector. You can see that I use a passive USB to PS/2 adapter for the keyboard and then I plug the mouse in normally. If you had both USB keyboard AND mouse then you would just use two passive adapters instead of one. From here for normal purposes (only one KVM switch) you would just plug the leads of the KVM switch into your machines and go.

With that said, my particular setup is a bit more elaborate. I have three monitors and three computers that I access all the time (two servers and my workstation). I have it set up so that normally all three monitors are connected to my workstation, but I can use the far left monitor for server one when needed and the far right monitor for server two when needed. I can view all three computers at once with this setup since the first KVM switch controls the leftmost monitor, the second KVM switch controls the rightmost monitor, and the center monitor is dedicated to the workstation via HDMI.

The second picture shows how I accomplish this with a second KVM switch. The first lead of the second KVM switch is attached to a dual PS/2 to USB adapter (because I have no more PS/2 ports) which is attached to my workstation. The first lead of my first KVM switch is also attached to my workstation. The second lead of my second KVM switch is attached to my second server and the second lead of my first KVM switch is attached to my first server. My second KVM switch does not have a dedicated keyboard, instead I use the fourth lead of my first KVM switch as the input of my second KVM switch (no adapters required because the leads of the first KVM switch are PS/2 as are the inputs to the second KVM switch). To avoid any device changing conflicts I had to change the escape sequence of my second KVM switch (from CTRL -> SHIFT -> ALT -> DEVICE_NUMBER to something different (I used ALT -> SHIFT -> CTRL -> DEVICE_NUMBER)).

Please let me know if any of this is unclear.

FIRST PICTURE alt text

SECOND PICTURE alt text

ubiquibacon

Posted 2010-09-08T06:05:47.447

Reputation: 7 287

1@typoknig Can you provide a source for "In most modern computers that still have ps2 ports, the ps2 bus is actually part of the USB bus."? – AndrejaKo – 2010-09-08T13:06:56.490

Magic, uh? i dont know what to think about that. Probably you dont know? – GetFree – 2010-09-08T19:08:17.033

Have you used both USB and PS/2 switches? I've heard that in USB switches the switching is not instantaneous, that it takes some time for the other computer to grab the input from mouse and keyboard. Have I heard wrong? – GetFree – 2010-09-08T19:12:08.180

@AndrejaKo, In was told that by an Asus tech who seemed to know what he was talking about at the time, but after researching the issue (due to your request for a source) I found that the the devices HID devices themselves are actually responsible for determining if they are connected to a USB or PS/2 port. I got this information from the Human interface devices (HIDs) section of the Wikipedia article on USB here http://en.wikipedia.org/wiki/Universal_Serial_Bus

– ubiquibacon – 2010-09-08T20:07:17.830

@GetFree, I have used both PS/2 and USB KVM switches and I have not noticed any difference between switching speeds. Right now I am using two PS/2 switches and I am running USB devices on both of them with no problems. I don't know how many ports you need on your KVM switch, but if you just need one extra port I would recommend the two port IOGear switch found here http://www.newegg.com/Product/Product.aspx?Item=N82E16817107407 I have the four port version of this switch and it is fast, small, and has been working good for over 5 years.

– ubiquibacon – 2010-09-08T20:15:13.963

@typoknig Thank you for taking time to look up a source for that. – AndrejaKo – 2010-09-08T20:31:02.307

@typoknig, USB devices on a PS/2 switch? How's that? – GetFree – 2010-09-08T23:02:30.007

@GetFree see my edited answer. – ubiquibacon – 2010-09-09T05:21:50.303

@typoknig, you could've just said that your switch supports both USB and PS/2 devices. It wasn't neccessary such a big explanation. Thanks for showing anyway. – GetFree – 2010-09-09T06:09:19.820

My switch does not support USB, it has no USB port, thus the adapter. There are switches that have both USB and PS/2 though. I didn't think you were understanding what was going on (due to your multi-part question) thus the thorough explanation :) I hope it helped you figure out whatever you are doing. – ubiquibacon – 2010-09-09T06:24:10.523

Then your keyboard is the one that supports both ways of communication, right? – GetFree – 2010-09-09T07:42:04.883

Yes, according to Wikipedia the HID (keyboard, mouse, ect) is what recognizes if it is plugged into a USB port or a PS/2 port. I think that the actual values sent when you press a key on your keyboard are the same for most keys regardless if the keyboard is USB or PS/2. I say this because I use to run a program called Grider, and it can provide you numeric values of the keys you press. The values of keys were always the same for me regardless if I was running a USB keyboard or a PS/2 keyboard EXCEPT for media keys like play, FF, FR, stop, volume knob, ect. In any event my KVM figures it out. – ubiquibacon – 2010-09-09T13:16:00.297

Alright, if you say they both switch equally fast, then I think I'll go for a USB switch. Here is a cheap one: http://cgi.ebay.com/270502954289

– GetFree – 2010-09-09T23:30:51.010

Your right, that is cheap. Make sure you account for the cost of extra VGA cables (unless you already have some) since that KVM does not come with leads attached... the one I gave you a link to does. – ubiquibacon – 2010-09-10T02:39:33.293

@typoknig, I just need the KM part of the KVM. So I just need two USB A/B cables which I already have. I just hope these cheap switches can handle the USB bus correctly so no weird things happen when pressing the button. – GetFree – 2010-09-10T07:34:11.067

It depend on switch model. Good ones present itself as keyboard and mouse for all PC even if real keyboard mouse not connected. – Mikhail Moskalev – 2010-09-10T11:25:20.167

@mmv-ru, I have yet to see a USB switch that does that correctly. – GetFree – 2010-09-11T01:03:26.947

@mmv-ru you are correct... even the PS/2 KVM switches do as much. – ubiquibacon – 2010-09-27T05:48:48.943

So does anyone have a recommendation for a USB/KVM switch that has drivers that present itself as an actual mouse/keyboard device to the PC it's connected to? In my opinion, if there's a 3-5 second delay in switching it's unusable. – boltup_im_coding – 2013-09-24T04:33:21.883

USB KVM vs. PS/2 KVM switches

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