Distribution amplifi er see Amplifi er, distribution.
Dot bar generator A device that generates a specifi ed output
pattern of dots and bars. It is used to measure scan linearity and
geometric distortion in video cameras and monitors. Also used for
converging cathode ray tubes.
DRAM Dynamic random access memory A type of computer
memory that is lost when the power is turned off.
Drive pulses Synchronizing and blanking pulses.
DSL Direct Subscriber Line A digital phone service that pro-
vides full voice, video, and digital data over existing phone systems
at higher speeds than are available in typical dial-up Internet
sessions. There are four types: ADSL, HDSL, SDSL, and VDSL. All
operate via modem pairs: one modem located at a central offi ce
and the other at the customer site. Asymmetric DSL technology
provides asymmetrical bandwidth over a single wire pair. The
downstream bandwidth from network to the subscriber is typi-
cally greater than the upstream bandwidth from the subscriber to
the network.
DSL Modem A modem that connects a PC to a network, which
in turn connects to the Internet.
DTV Digital Television Refers to all formats of digital video,
including SDTV and HDTV.
DVD Originally called Digital video disks, now called digital
versatile disk. These high-capacity optical disks now store every-
thing from massive computer applications to full-length movies.
Although similar in physical size and appearance to a CD or a
CD-ROM the DVD signifi cantly improves on its predecessors’
650 MB of storage. A standard single layer single-sided DVD can
store 4.7 GB of data. The two layer, single-sided version boosts the
capacity to 8.5 GB. The double-sided version stores 17 GB but
requires a different disk drive for the PC.

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