Specifications

Video DynaSync™

-P03-

Background – The Evolution of KVM Switches

KVM (Keyboard-Video monitor-Mouse) switches are a mature feature in modern data centers and now are com-

mon in the SOHO (Small Ofﬁ ce/Home Ofﬁ ce) desktop environment. Originally developed in the early 1990s as

Keyboard-Video monitor (KV) switches, and updated to include Mice when graphical operating systems with

mouse-controlled GUIs (Graphical User Interfaces) became popular in the mid 1990s, the KVM switch contin-

ues to offer the beneﬁ ts of both space and power savings. Instead of needing one monitor, one keyboard and

one mouse for every computer, a single set of these peripherals can be shared with a few or even thousands of

computers in ofﬁ ces and large data centers. The saved ﬂ oor and rack space and the saved electricity (for the

reduced number of monitors and for cooling their heat output) is substantial. Modern KVM switches also save a

lot of valuable time by offering users remote access up to 1000 feet away via Cat 5 cables, or up to thousands of

miles away via TCP/IP so busy, highly paid personnel don’t have to leave their desks to manage distant servers

and other computers.

Trends

While KVM switches have been evolving for almost two decades, in recent years the nature of the monitor itself

and of the video electronics in the computers have signiﬁ cantly changed. The “plain vanilla” VGA video outputs

and the simple multi-sync monitors of say 1999 have given way almost exclusively to LCD monitors and a vari-

ety of video interconnect schemes that include VGA as well as its higher resolution derivatives such as QXGA,

etc. Today we also ﬁ nd DDC (Display Data Channel) signals on VGA outputs, plus DVI (Digital Visual Interface),

and HDMI (High-Deﬁ nition Multimedia Interface) video, each of which incorporates different connectors, logical

handshakes and video formats.

Several aspects of this migration of video have made simple KVM switching a bit less than simple if one is to

be able to quickly and easily switch between a variety of computers without running into video roadblocks. For

one thing, LCD monitors typically have one “ideal” display resolution, unlike the older CRT video monitors. While

a given LCD may be able to display alternate resolutions, these will not be as sharp as its optimum resolution.

Consequently, the computers should, ideally, be set to drive the connected monitor at its optimum resolution. A

data structure known as EDID (Extended Display Identiﬁ cation Data) allows this automatic, optimized video set-

ting to be obtained when a suitably equipped computer graphics card and monitor are directly connected to one

another and the computer is booted up. Additionally, an increasing number of computers and digital peripherals

are equipped with HDCP (High-bandwidth Digital Content Protection) which involves a handshake between the

display port of the computer or peripheral and the monitor; this is intended to discourage unauthorized copying of

protected programming material. When a KVM switch is used with an HDCP-equipped system, this handshake

may fail to occur or may be broken when the display is switched among computers, thus frustrating legitimate

use of the system.