What's a KVM? Using the Aten CS22U Keyboard Video Monitor switch

I wrote here about running Anti Virus and Quicken 98 on an old Windows 98 PC.

I wanted to run that old PC via a keyboard-video-monitor (KVM) switch so that I could share my main PC’s monitor, keyboard and mouse between both PCs. I chose the Aten CS22U USB cable KVM from Amazon. It’s got two sets of moulded USB/ VGA leads that connect to two USB ports and video on each PC: some KVMs simply have ports that need separate leads to connect, adding to the cost and hassle.

Aten CS22U KVM has a separate changeover switch (circled) to toggle between PCs. Click to view.The monitor, keyboard and mouse connect to VGA and USB input ports on the KVM. I also chose this device because it has a separate selector switch on a flying lead to stick on your desk, to change from one PC to the other. Two LEDs confirm the state of the KVM.

Many KVMs poll for a sequence of keystrokes to switch over. In the past I’d been hit by stupid problems such as a Linksys KVM needing a double scroll-lock keystroke, only to find that there’s no scroll lock button on the keyboard (eg some Logitech models). In that case I managed to separately program a key as a scroll lock key, using a second ‘temporary’ keyboard and the workaround found at http://www.diy-forum.net/re-kvm-switch-t178986.html

Many “intelligent” keyboards and mice with extra features (hot keys, extra function keys, volume controls etc.) don’t work fully using a KVM, but the basic features should hopefully work OK.

My main (XP) PC has a Logitech MX1000 Laser USB wireless mouse and wired Microsoft USB keyboard, so the first question was whether they would run on W98. I found that Logitech's Setpoint V3.1.116 driver software installed and worked fine with the Logitech mouse. Infact it looks better than the later bland-looking Logitech software.

All Logitech's drivers including legacy ones are online at their FTP site here.

I also found that the W98 default keyboard driver provided the basic functionality I needed.  Some features (eg the keyboard volume control) are ignored though.

The keyboard and mouse connections were easy, thanks to the KVM’s flying leads. However my main PC runs a DVI display, but the old W98 PC has a VGA output. The KVM has a VGA port only (I have yet to find one with a DVI port.)  So how to configure this lot to work together?

Luckily, my Viewsonic VP2250 monitor has dual inputs, DVI and VGA. Eventually I worked out a scheme as follows:

1. The Windows 98 VGA card was hooked directly to the Viewsonic monitor’s VGA input, with one of the KVM’s  VGA leads.*
2. The DVI port of my main PC was connected directly to the Viewsonic’s DVI input.
3. The Aten KVM push button switch therefore toggles the keyboard and mouse only;
4. The monitor’s input select switch toggles the display between VGA and DVI.

*The KVM’s unused VGA lead was blanked off with a plastic cap.

Happily, I found that the video signal changed automatically when the KVM was switched from one PC to the other, but the monitor’s input select switch needed pressing to revert the display back the other way.

I do notice immediately the W98’s fuzzier VGA image compared with the DVI image running in the monitor’s resolution. However it’s tolerable.

LED indicators on the KVM show (if you’re near enough) which channel is selected, and of course the Windows XP machine will “bing bong” or “bong bing” audibly depending on whether the USB keyboard and mouse are being connected or disconnected, respectively.

The Aten CS22U KVM proved to be ideal for switching a USB keyboard and mouse between two PCs, using DVI and VGA video signals on a dual-input monitor. Without the dual video input capability of my monitor I doubt that there’s a solution to this problem.

Make sure that both PCs will work with your keyboard and mouse before investing in a KVM though.

You can buy the Aten CS22U from Amazon.

Updated in 2014:

In May 2014 I upgraded to a (great!) iiyama XB2380HS monitor which has DVI and VGA inputs. My problem is still how to use an Aten CS22U KVM to switch between an old PC with a legacy VGA video, and a newer PC with a DVI video card.

The answer is to use the monitor’s Input Select to switch between VGA and DVI and so I continued with my KVM scheme as follows:

1. The Windows 98 VGA card was hooked directly to the iiyama monitor’s VGA input, using one of the KVM’s VGA leads. That’s also because I didn’t have a long enough VGA lead to go end to end.
2. The DVI port of my Windows 7 PC connects directly to the iiyama DVI input.
3. The Aten KVM pushbutton switch therefore toggles the keyboard and mouse. At the same time it toggles the VGA signal.
4. The monitor’s input select switch toggles the display between VGA and DVI.
5. As a bonus, the W98 sound output was fed into the monitor’s audio input using a 3.5mm stereo extension lead. I could then hear that PC over the screen.

The iiyama’s main Menu system is used to select ‘Auto’ as the Input source. Then the left-hand button labelled Auto, is used to choose between VGA (D-sub) or DVI. It toggles between the two PCs perfectly, but there is a few seconds time lag.

Using a KVM with a VGA and DVI PC (click to see)

The Aten CS22U is perfect for this and has saved the cost of upgrading everything to DVI.

Comments

[SimpleCAD]

I have one of these and I am trying to switch video as well. Everything 'works' except that one PC (XP64) recognises the monitor as only 1280 x 800 when it is actually 1680 x 1050. The other pc (XP32) recognises the monitor as 1680 x 1050.
I have rebooted a heap of times but the 1280x800 resolution is the highest that I can select if I go to change resolution manually.
Any ideas?

[Alan W]

It might be down to the capabilities of the video cards themselves. If they can't resolve down to that resolution then maybe a driver upgrade might help, but I doubt it. Compare the specs of the video cards.

[SimpleCAD]

Thanks for your feedback. Although Windows' setup would not allow it, I was able to manually set the resolution to 1680x1050 from within Nvidia's setup software. Have rebooted a few times and everything appears alright. (My other monitor is 2560x1440 and both cards drive this ok.)

[PM]

Does anyone knows if data could transfered accidently from one pc to the other during use or during switching so that viruses can transfered ?

[Alan W]

Virus-infected files could be transferred that way [if they share a network and files are accessed over the LAN - the KVM won't prevent that happening], you just have to hope that your anti virus software will intercept them if/ when they are opened. I have had that happen to me between two PCs over a LAN. I rebuilt a PC from scratch and hooked it onto my network before I'd managed to put AV in, and it got infected. That taught me a lesson.

[I added the bit in brackets on 16th August.]