2007 ATEN Technology, Inc. www.aten-usa.com
Why Network Administrators Should Explore the “V” in K-V-M Switches
Video Display Formats – Which one is Best?
-P04-
CRT Paves Way for LCD
The biggest impact in computer video has been the shift from CRT (cathode ray tube) to fl at screen
monitors. Typically, the fl at screen used in a data center is an LCD (liquid crystal display) though some
plasma and other technologies are used for larger screens. These monitors have emerged as an at-
tractive option due to lower energy usage, reduced footprint, and greater edge-to-edge sharpness.
The combination of its resilience (LCDs last three times longer than a CRT) with affordability over the
last few years has made the LCD a much more affordable alternative. LCDs are now the de-facto stan-
dard for the desktop, server room and data center. This swing towards LCDs has contributed to a
resurgence of digital video output cards.
Analog Returning to Digital?
While early LCDs almost universally included VGA input connections, the LCD monitor is an inherently
digital display device with specifi c transistor junctions controlling each pixel on the screen; this differs
from the CRT, where early digital signals had to be reconverted back to analog to drive the electron
gun and defl ection magnets that ‘painted’ the electron beam across the phosphor-coated screen sur-
face. To address this issue, many LCDs, particularly larger screens, now offer both DVI (Digital Video
Interface) and VGA (analog) connections.
Display Data Channel
The Display Data Channel or DDC describes a digital link, or a channel between a computer display
and a graphics adapter, that allows the display to communicate its specifi cations to the adapter. The
DDC standard was created by the Video Electronics Standards Association (VESA). DDC uses 3 pins
(data/clock/ground) which may be carried in a VGA, DVI or HDMI connector.
Which display format is best? Then answer depends on the application and the source of the video. In
terms of KVM technology, the VGA input is the best choice – the white paper will discuss this in more
detail in the next section.
Analog-Only VGA vs. DVI-I Combination Digital-Analog Video Male Connectors
(Dual link DVI sources have higher resolution than Single link DVI sources)
(23 Seiten)
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