In my job, I work on multiple operating systems. Years ago, to save money, I set up my PC for "multiple boot", which meant that I could have up to four operating systems on the primary disk (providing there was sufficient room.) I did this because my work required that I use multiple versions of Windows. I was also interested in tinkering with other systems, like Netware, OS/2, Coherent (a Unix clone) and an upstart called Linux. There's a program (by V Communications) called System Commander that makes OS selection possible, but rebooting a PC has never been what I'd call "convenient" in any operating system. (System Commander not the only OS-selection program, but it's by far the best, being most flexible and easy-to-use ) Therefore I didn't tinker as much as I would have liked to, since my work and my day-to-day operations were on Windows; I tended to stay in Windows through sheer inertia.Switch Pitfalls
Luckily, technology fixed that problem for me. PC's became cheaper, and though I worked hard to upgrade the ones I had, at some point it made sense to buy a new one. In the early days, I'd give the old system away to a computer-less family member, but soon they all had their own, so I'd just keep my old systems and add them to my network. As newer systems became more common, I began to accumulate older systems from family, friends, and colleagues, all of which which I'd upgrade and put into service. Soon it was no longer necessary to put multiple systems on a PC, because I had multiple PC's. That created a new problem - what to do with all those monitors, keyboards, and mice?
The answer was obvious: since one person can only work on one system at a time, the solution was some sort of a switch which would allow me to use a single monitor, keyboard and mouse to control multiple systems. These devices are called KVM switches (for keyboard, video, mouse) and were pretty primitive in the beginning. My first switch was just that: a totally passive device in a metal box, which could switch the required multiple lines in parallel. At the back of the box were three sets of connectors: three SVGA video connectors, three AT-style keyboard connectors, and three nine-pin serial ports. It allowed the user to connect one keyboard, monitor, and mouse to two different systems. It worked, but not well- the video would jump when I switched it, and the keyboard would sometimes get locked up, caused probably by switching in the middle of a clock pulse. Clearly, something better was required.
The next generation of KVM switches were active. That is, they contained circuitry to make the switchover from one system to another go more smoothly. Since the switch hardware was electronic rather than mechanical, the device could also be smaller. My first electronic switch was a four-port model by LinkSys. It worked quite a bit better than the mechanical version, avoiding most of the "jump" and "lockup" problems. It was, of course, more than twice as expensive than the simple "box," but it was worth it. And though it was electronic, it derived its power parasitically from the system (PS/2 ports have 5V power and ground lines) connections, so it didn't require an external power source. There were other advantages as well. Because it was electronic, it didn't require a big rotary switch; all I had to do was push a single button in front, and it would cycle the display between computers 1, 2, 3, and 4, and then back to 1. It was also set up to trap a key sequence so that a particular system could be selected from a keyboard. The sequences all started with Alt-Ctrl-Shift, where the three keys were not pressed simultaneously but in quick succession . The fourth keystroke was the number of the desired PC - 1, 2, 3, or 4. This made switching between different systems pretty convenient. Of course, I should note that technology had changed since I bought the original switch; this one now had PS/2 connectors for both the mouse and keyboard ports.
Figure 1 - LinkSys 4-Port KVM switch with two systems attached. Cables to monitor, etc. at back.
I still use that switch; though I've updated my newer systems to a Belkin 4-port switch (for technical reasons that I'll list later.) It's a great convenience to me. I have two tower systems, one running Windows 2000 and one running Linux. I also have two notebook PC's in this setup. One of the notebooks is the one I currently use while on the road; but when at home, it's nice to be able to use it with a better screen and a more ergonomic keyboard and pointing device (personally, I prefer a trackball to a mouse, but I admit that's an eccentric acquired taste.) The other notebook is so beat-up that it's no longer good for traveling, but it still works, and it's useful as a test platform.
But I must admit that there are drawbacks, tradeoffs and gotchas with the use of a KVM switch. It's probably not the right solution for everyone, and there are alternatives (though those have their drawbacks as well.)
What type would I recommend? As far as electronic switches, I have investigated several, but have actually used only Linksys and Belkin. Although this is by no means an exhaustive list, the two types illustrate some typical features and options. KVM switches most commonly come in two or four-port versions, though I have seen up to eight ports on a single switch. You can utilize more switches by selecting a switch with a master/slave option. The Belkin model I have can be used to daisy-chain up to four banks of switches, for a total of sixteen PC's controllable by a single monitor, keyboard and mouse. Because of its additional features (especially the serial-to-PS/2 mouse converters) the Belkin requires its own power supply, a standard "wall wart" transformer.
The Linksys switch was less expensive, but is not designed to be extendable. As I said before, it doesn't have its own power supply. But its simplicity allows for easier operation when switching between screens. Since it handles only four screens, the screen number is specified by a single digit (hot key sequence Alt-Ctrl-Shift-N) Because the Belkin can be extended, you must specify a bank number, even if there's only one bank, thus the more complicated hot-key sequence: ScrlLock-ScrlLock-Zero-N. Of course, you could extend the Linksys by connecting the output of additional switches to one or more of the its four inputs, but I wouldn't recommend it, since the switches would then have to draw their power from each other.
As I said before, another consideration is the vintage of your PC's. Since everything seems to be going to USB, newer KVM switches incorporate USB connectors instead of PS/2. Most still have SVGA connectors for monitors, but the newer monitors use USB as well. Many people may be tempted to use a simple four-port USB switch and daisy-chain the monitor, keyboard, and mouse on the other side, but I wouldn't recommend that. The switch must be able to emulate all of your USB devices so that when a particular PC is selected, the devices do not "disappear" for the other systems. And of course, if you want to add a Macintosh to the mix, you will require an adapter cable for the video, and (for older systems) ADB-to-PS/2 adapters for mouse and keyboard.
So, although KVM switches have their problems, I'd definitely
recommend them to anyone who is into multi-platform development, or even
just experimenting with different distributions. They're also good if you
end up installing or re-installing on a regular basis. Best of all, they
save space, and don't require you to move from one desk to another when
operating in cross-platform mode.
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This page Copyright 2002, Nakota Software, Inc.
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