Specifications

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Appendix A Glossary
from 655 to 2,125 scanning lines, having an aspect
ratio of 5:3 (or 1.67:1) and a video bandwidth of
30MHz–50MHz (5+ times greater than the NTSC
standard). Digital HDTV has a bandwidth of
300MHz. HDTV is subjectively comparable to
35mm film.
High Definition Multimedia Interface
(HDMI) A digital audio/video interface support-
ing uncompressed data on a single cable.
High Density Digital Versatile Disc (HD-
DVD) One of the two competing high-definition
DVD format standards. Also see Blu-ray Disc.
high frequency (HF) The frequency band
between 3 and 30MHz.
high-level formatting Formatting performed
by the DOS FORMAT program. Among other
things, it creates the root directory and FATs.
history file A file created by utility software to
keep track of earlier use of the software. Many
backup programs, for example, keep history files
describing earlier backup sessions.
hit ratio In describing the efficiency of a disk or
memory cache, the hit ratio is the ratio of the
number of times the data is found in the cache to
the total number of data requests. 1:1 is a perfect
hit ratio, meaning that every data request was
found in the cache. The closer to 1:1 the ratio is,
the more efficient the cache.
HMA (high memory area) The first 64KB of
extended memory, which typically is controlled by
the
HIMEM.SYS device driver. Real-mode programs
can be loaded into the HMA to conserve conven-
tional memory. Normally, DOS 5.0 and later use
the HMA exclusively to reduce the DOS conven-
tional memory footprint.
HomePNA A home networking standard using
existing home or office telephone wiring to obtain
speeds up to 11Mbps.
HomeRF A wireless home network using radio
waves to obtain speeds up to 11Mbps.
horizontal scan rate In monitors, the speed at
which the electron beam moves laterally across the
screen. It’s normally expressed as a frequency; typi-
cal monitors range from 31.5KHz to 90KHz, with
the higher frequencies being more desirable.
host The main device when two or more devices
are connected. When two or more systems are con-
nected, the system that contains the data is typi-
cally called the host, whereas the other is called the
guest or user.
host protected area A technique used in ATA-7
and newer ATA drive specifications for reducing the
reported size of the hard disk. The space not
reported is used to store system recovery data.
hotfix A software patch for a Microsoft applica-
tion or operating system. Hotfixes can be down-
loaded individually from the Windows Update
website or as a service pack. Microsoft also calls
them quick fix engineering (QFE) files.
hot-plug RAID memory A memory technol-
ogy used on servers to permit hot-swapping of
defective memory modules without loss of memory
contents. Memory modules form a RAID array simi-
lar in operation to a RAID 5 disk array.
HPT (high-pressure tin) A PLCC socket that
promotes high forces between socket contacts and
PLCC contacts for a good connection.
HST (High-Speed Technology) The now-
obsolete U.S. Robotics proprietary high-speed
modem-signaling scheme, developed as an interim
protocol until the V.32 protocol could be imple-
mented in a cost-effective manner.
HT technology See hyper-threading technology.
HTML (Hypertext Markup Language) A lan-
guage used to describe and format plain-text files
on the Web. HTML is based on pairs of tags that
enable the user to mix graphics with text, change
the appearance of text, and create hypertext docu-
ments with links to other documents. See also
DHTML.
HTTP (Hypertext Transfer Protocol) The
protocol that describes the rules a browser and
server use to communicate over the World Wide
Web. HTTP allows a web browser to request HTML
documents from a web server. See also hypertext.
HTTPS (Hypertext Transfer Protocol Secure)
An extension to the HTTP protocol that provides
for sending data securely over the Internet.
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