Best Practices Feature Set

By Nigel Dickens  |  Posted 2009-05-14 Print this article Print

Best practices feature set

Even though traditionally a technology for larger server rooms, you want a "CATx" switch. When you really look at the feature set, it's perfect for a small server room. These switches use a small "dongle" that connects to the computer, and cheap, thin, ubiquitous CATx (for example, CAT5, CAT5e, CAT6, etc.) cable to connect the dongle to the KVM switch. This approach has several advantages.

First, the dongles enable the KVM switch to be connected to any computer by simply choosing the right dongle (for example, PS/2, USB, Sun, etc.). Second, internal "keep alive" circuitry within the dongles means that the KVM switch can be disconnected or repowered without affecting the computers.

Third, the CATx-style cables mean that the KVM switch itself can be physically small, rather than half the size of a bus-always important in small server rooms that quickly become cramped.

Last, but by no means least, the CATx cables are much thinner and easier to manage than more traditional, bulky KVM cables-which are cumbersome to route around and under racks and equipment shelves. If you pile up the number of KVM cables you may need to connect, say, 10 computers, the space that traditional cables occupy can be quite astonishing. With more computers, the problem just gets worse.

In comparison, CATx cables take up relatively little space, and have the advantage of being disconnected at both ends, neatly fed through small holes and routed easily around corners.

A few more pieces of shopping advice: It's always worth getting a KVM switch with an On-Screen Display (OSD) because you won't always remember which computer you've connected to which port. And if you're planning to use a USB keyboard, it's worth checking that your new KVM switch supports USB on the KVM console end. Most CATx-style KVM switches support a choice of connections, so you shouldn't have a problem.

Also, make sure you get a switch with expansion or cascade ability. The number of servers you have will likely grow, so don't think that you can just connect one to another. This may be electrically possible, but if it's not a fully-designed cascade strategy, it will leave you with a whole load of operational confusion.

Potential problems

One potential problem to be aware of is Display Data Channel (DDC) support, which can cause significant frustration. Some switches offer no DDC support; others switch the DDC signals to the monitor when the computer is selected. Others present fixed DDC Extended display identification data (EDID) data. But the most sophisticated will clone the EDID data from the connected monitor.

These distinctions really matter if you want the computer to output the right video mode and you don't want to have to switch to each computer as they power up. The safest option is to choose a KVM switch that clones its DDC EDID data. One aspect that you won't often see on a KVM switch vendor's spec sheets is the switch's latency characteristic but it's nevertheless important.

Nigel Dickens has been Adder's Technical Director since 1991. He has over 20 years experience in the electronics industry. Nigel has a strong background in electronic engineering and a keen interest in mechanical engineering and design. He is a Chartered Engineer and a graduate in Electronics from Cambridge University. He can be reached at

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