When choosing a KVM switch, the task can become difficult if you do not know exactly what you need. When you are shopping around, you will need to know how many different computers or servers you are trying to control. Keep the future in mind. This will allow you to get a KVM switch that has enough room for your current needs and expansion. Typically KVMs come in 4 port KVM switches, 8 port KVM switches, and enterprise switches can have upwards of 64 server ports or more.
If you think you are going to expand your data center, a KVM switch with the ability to be cascaded can give you the ability to control 10s of thousands of servers from one location! Another important factor is whether or not you have USB or PS2 connections. If you have purely USB, a USB KVM switch may be your best option. If you have a mixture of PS2 and USB keyboard and mouse connections, you will want to make sure that you have a KVM switch that can do the conversion. So now you have your correct sizing needs covered, your peripheral needs covered, and next thing would be what platform your servers are.
KVM switches are most typically PC based in their more basic forms, but multi-platform KVM switches can handle SUN, UNIX, and MAC platforms. When the KVM switch is emulating the keyboard and mouse to the system, it is dependent on the platform to provide the correct type of emulation. Also as with USB KVM switches and PS2 KVMs you can mix and match, and a very good KVM switch will be able to handle all of these. Also another key area of choosing a KVM switch is knowing how many users will need to have independent access to the KVM switch. If you need four people controlling your sixteen servers, then you will need a KVM switch that can handle 4 users. If you would like for a user to be able to view the server from anywhere in the world you will need a KVM over IP solution, as described in detail on my blog which can be found in the link below.
KVM over IP solutions can be very versatile in many applications, and can cut down labor costs of having to pay someone to be on site with your equipment. Outside of the KVM realm there is a whole line of different data center products that you can control over IP. With a very sophisticated setup you could control servers, power, and even monitor all of your server rooms environmental factors all through an IP address.
A less common KVM solution, but one that I still get asked about is secure KVM switching. Secure KVM switches isolate electrical paths on the ports of the KVM switch and leave no traces of interference for snoopers to pick up on. A secure KVM switch can be very useful for a computer switching between secure and unsecure networks. These are usually only recovered by the government. For more KVM education please check my blog.