Operating instructions

DPI (dots per inch) A measure of printer resolution that counts the dots the
device can produce per linear (horizontal) inch.
DRAM (dynamic random access memory or dynamic RAM) The memory used
to store data in most personal computers. DRAM stores each bit in a “cell” com
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posed of a transistor and a capacitor. Because the capacitor in a DRAM cell can
only hold a charge for a few milliseconds, DRAM must be continually refreshed,
or rewritten, to retain its data.
DS3D (DirectSound3D) Introduced with DirectX 3.0, DS3D is a command set
used to create positional audio, or sounds that appear to come from in front, in
back, or to the side of a user. See also DirectX.
DSL (digital subscriber line) A high-speed Internet connection technology
that uses a regular telephone line for connectivity. DSL comes in several variet
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ies, including Asynchronous (ADSL) and Synchronous (SDSL), and many
speeds. Typical home-user DSL connections are ADSL with a download speed
of up to 1.5 Mbps and an upload speed of 384 Kbps.
DSP (digital signal processor) A specialized microprocessor-like device that
processes digital signals at the expense of other abilities, much as the FPU is op-
timized for math functions. DSPs are used in such specialized hardware as
high-speed modems, multimedia sound cards, MIDI equipment, and real-time
video capture and compression.
DTS (Digital Theatre Systems) A technology for sound reductions and chan
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neling methods, similar to Dolby Digital.
dual boot Refers to a computer with two operating systems installed, enabling
a user to choose which operating system to load on boot. Can also refer to kick
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ing a device a second time just in case the first time didn’t work.
dual-channel memory A form of DDR and DDR2 memory access used by
many motherboards that requires two identical sticks of DDR or DDR2 RAM.
duplexing Also called disk duplexing or drive duplexing. Similar to mirror
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ing in that data is written to and read from two physical drives, for fault toler
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ance. Separate controllers are used for each drive, both for additional fault
tolerance and additional speed. Considered RAID level 1.
Duron A lower-cost version of AMD’s Athlon series of CPUs.
Passport / Mike Meyers‘ A+ Certification Passport / Meyers / 226308-3 / Glossary
24 MIKE MEYERS’ A+ CERTIFICATION PASSPORT
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