What is a KVM Switch?

KVM stands for Keyboard, Video and Mouse, and a KVM Switch allows you to control two or more computers from a single keyboard, monitor and mouse. KVM Switches are sometimes also known as PC Switches, Server Switches and CPU Switches.

Why do I need a KVM Switch?

It is becoming increasingly common for users to have a group of servers that they only access infrequently and providing each server with its own keyboard, monitor and mouse requires the purchase of unnecessary hardware as well as taking up valuable space and using power. But anyone needing to control more than one computer will benefit from a KVM switch, savings in hardware alone will cover the purchase price plus the hidden savings in time and energy. There are several other substantial benefits from using a KVM switch: you can access all your computers through your best monitor, keyboard and mouse; KVM makes life easier - you work from one desk simply switching between computers and KVM helps improve productivity by running different applications on different computers simultaneously.

KVM switches vary, from small compact desktop models that can be sited on or near a desk to larger sophisticated rack-mounted switches that have multiple ports and are designed for complex server management applications.

Why can't I use a manual switch?

The technology used for manual switches is crude and the physical switching soon wears out the contacts causing poor video quality. Manual switches don't have a two-way communication with the mouse and keyboard, when the computer powers on it looks for a response from the mouse and keyboard, an intelligent KVM switch emulates the connection electronically and sets their functionality and characteristics. With a manual switch the connection is lost every time it's switched off, the switches have very limited functionality and are not recommended for a professional environment or where the switch is in constant use.

How does a KVM switch work?

A KVM switch is two devices in one box: It comprises a video switch that switches analogue video and sync pulses between shared monitors and computers and a microprocessor controlled system that sends and receives keyboard and mouse data and emulates the presence of keyboards and mice when they are not connected directly to the computer.

Will installing a switch cause problems with my existing software and hardware?

A KVM switch is a hardware device that is software independent so connecting it to a computer is the same as connecting a keyboard or a mouse, it doesn't require any software to install it and will not interfere with any programs that are running. Occasionally there are compatibility problems with connectors on older PCs. Most PCs have PS/2 mini DIN connectors but some old systems have 5 pin DIN and RS232 mice. To ensure compatibility with all combinations of computers, it is very important to purchase a KVM switch that supports both types from the same keyboard and mouse.

All Adder KVM switches support mixed RS232 PS/2 mice and PS/2 and 5 pin DIN keyboards in a seamless system.

How do the Extender products work?

KVM cables are usually coaxial video and keyboard/mouse cables that are bulky and expensive and limit the distance from the computer to about 30m to achieve an acceptable quality. Twisted pair cables are a more cost effective option for transmitting video but show high loss of video signal over distance and the video becomes unusable. A twisted pair extender overcomes this loss by amplifying the degraded signal to exactly match the loss.

AdderLink and AdderLink GOLD CAT 5 extenders work in pairs using a transmitter to receive the KVM signals from the CPU and sending the signal, across a twisted pair CAT 5 cable, to the receiver connected to a remote KVM station. AdderLink GOLD is unique in providing the flexibility of an integrated KVM switch in the receiver to connect a local CPU as well as KVM control at the transmitter for local control and it also provides stereo audio and microphone connections at both transmitter and receiver.

Which KVM Switch do I need?

There is a considerable choice of KVM Switches designed and developed for different end user needs. The key factors in choosing the right Switch for your needs are:

• How many computers do I want to control?
• Do I need a high screen resolution for my application?
• Do I want the switch on my desk or remotely controlled from a rack?
• Am I likely to increase the number of computers under my control so I'll need to cascade multiple switches with no loss of data quality?
• Do I need an on-screen display to make channel selection easier?
• How far from my desk do I want to site my computers?
• Do I need a local keyboard, monitor and mouse connection for controlling the computers when I'm in the server room?
• Do I operate in a multi-platform environment and need to switch seamlessly between systems?

Use the table below to check out the key features and help you decide which type of KVM Switch is right for you:

Product	No Ports	Screen Resolution	Desktop or Rackmount	Cascadable	Max cable distance	Local KVM control	On screen menu	Operating Systems
AV2	2	1900x1440	Desk	Yes	3m > cpu 2m > kvm or up to 200m with AdderLink			Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware
AV4	4	1900x1440	Desk	Yes	With PSU 30m > cpu 10m > kvm or up to 200m with AdderLink			Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware
AV4OSD	4	1900x1440	Desk or rack	Yes, 300 computers supported on OSD	3m > cpu 2m > kvm or up to 200m with AdderLink		Yes	Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware
AV8OSD	8	1900x1440	Desk or rack	Yes, 300 computers supported on OSD	3m > cpu 2m > kvm or up to 200m with AdderLink		Yes	Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware
AV4USB	4	1900x1440	Desk	No	3m > cpu 2m > kvm or up to 200m with AdderLink			Windows 98, 2000. Mac 8.6 on
AV4USB Mac	4	1900x1440	Desk	No	3m > cpu 2m > kvm or up to 200m with AdderLink			Windows 98, 2000. Mac 8.6 on
SV2	2	1900x1440	Desk	Yes	30m > cpu 10m > kvm or up to 200m with AdderLink			Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware
SV4	4	1900x1440	Desk or rack	Yes, 300 computers supported on OSD	30m > cpu 10m > kvm or up to 200m with AdderLink			Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware
SV4Pro4	4	1900x1440	Rack	Yes, 300 computers supported on OSD	30m > cpu 10m > kvm or up to 200m with AdderLink	Yes	Yes	Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware
SV4Pro8	8	1900x1440	Rack	Yes, 300 computers supported on OSD	30m > cpu 10m > kvm or up to 200m with AdderLink	Yes	Yes	Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware
SV4Pro12	12	1900x1440	Rack	Yes, 300 computers supported on OSD	30m > cpu 10m > kvm or up to 200m with AdderLink	Yes	Yes	Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware
SV4Pro16	16	1900x1440	Rack	Yes, 300 computers supported on OSD	30m > cpu 10m > kvm or up to 200m with AdderLink	Yes	Yes	Windows 3.x, 95, 98, NT, 2000, Unix, DOS, OS2, Netware

What are the important features I should look for when purchasing a KVM Switch?

Hot pluggable - you can connect to running PCs without needing to re-boot, this is particularly important in a busy multi-server environment

Keyboard and mouse emulation - some computers shut down if they don't detect keyboard and mouse connections, this allows the computer to 'see' the keyboard and mouse as though they were connected directly

Automatic mouse translation - lets you use a PS/2 type or Intellimouse with any attached server whether the computer has a serial mouse port or a PS/2 port

SmartBoot - continuous keyboard and mouse emulation ensures reliable bootup of all machines

Non-proprietary cables - no need to buy special cables, uses standard cable connections. Best results are achieved using high quality tri-coax cables.

On-screen display - facility to name each connected computer, very important if you are connecting more than four servers. Adder's OSD also has a menu to give a positive confirmation when you have connected to a selected computer

Front panel button, hot key and mouse channel switching - when using a KVM switch all the time the ability to make a 'quick fire' change becomes very important.

Video Quality - High screen resolution with no loss of quality over extended distances

Size and construction - for convenience look for switches that are designed to be rack mounted or are robust enough to stand a monitor on

Data activity indicators - you need to know if there is no activity from a connected computer

Prompt and Stream mode mouse operation - Some KVM switches operate mice in prompt mode only, Adder KVM switches operate both prompt and stream mouse communication allowing portable computers such as the IBM ThinkPad to be supported.

I now know that I need a KVM Switch, I know the size of my installation and what type of Switch I need and I understand the importance of the various features. Which other factors should I take into account when purchasing a KVM Switch?

If you are using a KVM switch to access and control mission critical servers then you need to ensure you chose a highly reliable switch - it needs to be more reliable than the computers it controls! If one computer goes down it's only a single problem, if your KVM switch fails you lose control of all the connected computers.

When a KVM Switch is doing its job then the Switch itself has little importance to the user, how it looks or what it cost are not really very significant in the long run. However, if your Switch fails to deliver on its functionality or breaks down frequently then you will have a major problem as the Switch is the access to your computers.

There are subtle differences to be found between PS/2 communications signals in different products, leading KVM switch manufactures will have developed products that overcome incompatibilities caused by signal variations but not all KVM switches are developed and manufactured to the same standard so it is important to buy from a company with a reputation for product performance and reliability.

Pros and Cons KVM Switches

Daisy chaining

Many KVM switches let you daisy chain to increase the number of servers under your control. Daisy chaining is a linear configuration and as well as limiting the physical distance between machines you also lose video quality as the signal travels down the chain. Cascading switches in a tree configuration is more flexible, there is little loss of video quality and units under control can be placed further away from the controlling KVM station.

Keyboard and Mouse re-set feature

These are put on KVM switches as a 'fail-safe' for users but shouldn't be needed if the KVM switch is working properly.

No power supply unit

Switches that don't have the facility to add a PSU should be avoided. At some time you may need to run video only from your switch and a KVM switch derives its power from the connected mouse and keyboard. If you want to control your computers at a distance a PSU will be needed to boost the signal.

Single processor per port

A good processor should support all ports simultaneously, having a processor for each port means paying for more resources than you need.

Automatic compensation on extender products

Although it can be useful, automatic compensation takes the control out of the users hands, with manual control you can set the compensation to your own requirements.

Self-powered

All Adder KVM switches are designed to be powered by a single connected computer, beware self-powered switches that don't make this claim because if you switch the computers off, leaving one on, you'll crash!