| gauss |
| A unit of measurement of
magnetic intensity named after Karl F. Gauss (1777-1855), considered
to be one of the greatest mathematicians of all time. See degauss. |
|
| GB |
(1) (GB) (GigaByte)
One billion bytes (technically 1,073,741,824 bytes). See giga
and space/time.
(2) (Gb) (GigaBit) One billion bits
(technically 1,073,741,824 bits). Lower case "b" for bit
and "B" for byte are not always followed and often
misprinted. Thus, Gb may refer to gigabyte. See giga
and space/time. |
|
| GHz |
| (GigaHertZ) One billion
cycles per second. High-speed radio frequency applications transmit in the gigahertz
range. See RF. |
|
| GIF |
(Graphics Interchange Format)
A popular bitmapped graphics file format developed by CompuServe. It supports 8-bit color
(256 colors) and is widely used on the Web, because the files compress well. GIFs include
a color table that includes the most representative 256 colors used. For example, a
picture of the forest would include mostly greens. This method provides excellent realism
in an 8-bit image.
There are two versions of GIF. The original GIF87a was created in 1987, and GIF89a in
1989. GIF89a allows one of the colors to be made transparent and take on the background
color of the underlying page or window. GIF89a also supports animated GIFs, which are GIF
sequences displayed one after the other to simulate movement.
Macintosh users call GIF files "giff" files, while PC users call them
"jiff" files. See LZW.
GIFs and JPEGs
Both GIF and JPEG images are widely used on the
Web, are supported by Web browsers and other Web software, and both kinds are routinely
used on the same Web page. The choice is usually a simple one. Charts, screen shots and
technical drawings are compressed best as GIFs, plus GIFs only hold up to 256 colors
(8-bit color). Most all photographs are better as a JPEG, which supports 24-bit color and
has the option of several compression levels (the choice depends on how much degradation
you can tolerate). Save a scanned image in both formats and you will often see a dramatic
difference in file size, which is a critical issue when retrieving Web pages.
The Patent Issue
The GIF format uses the LZW compression algorithm that is owned and
patented by Unisys. According to Unisys, the publisher of any application that reads and
writes GIF images is required to obtain a license and pay the appropriate fees for the use
of the LZW algorithm. This does not apply to the end user downloading GIFs. It applies to
the creator of any image processing software that inputs and outputs GIFs. For example,
the publisher of the browser you use to display your GIFs would be responsible for this,
not you as a user of the browser. |
|
| giga |
| Billion. Abbreviated "G." It often
refers to the precise value 1,073,741,824 since computer specifications are usually binary
numbers. See GB. |
|
| gigabit |
| One billion bits. Also Gb, Gbit and G-bit. See
giga and space/time. |
|
| Gigabit
Ethernet |
An Ethernet
technology that raises transmission speed to 1 Gbps. Used mostly for
backbones, the first IEEE standard (802.3z) for Gigabit Ethernet (GigE)
was defined in 1997 for use over multimode optical fiber. 802.3z
provides full-duplex operation from switch to end station or to
another switch and half-duplex using CSMA/CD in a shared
environment.
In 1999, the 802.3ab standard (1000Base-T) allows Gigabit Ethernet
to run over Category 5 copper cable, enabling GigE devices to be
readily installed in 100BaseT networks without cable changes. The
maximum distance between nodes is based on the type of transceiver
and cable used as outlined below.
8B/10B Encoding
Fiber Modal
Diameter Bandwidth Range
(microns) (MHz-km) (meters)
1000Base-SX (802.3z)
62.5 multimode 160 220
62.5 multimode 200 275
50 multimode 400 500
50 multimode 500 550
1000Base-LX (802.3z)
62.5 multimode 500 550
50 multimode 400 500
50 multimode 500 550
9 singlemode --- 5000
1000Base-CX (802.3z)
Shielded twisted 25
pair copper
1000Base-T Encoding
1000Base-T (802.3ab)
Category 5 UTP 100
|
|
| gigabyte |
| One billion bytes. Also GB, Gbyte and G-byte.
See giga and space/time. |
|
| gigaflops |
| (GIGA FLoating point OPerations
per Second) One billion floating point operations per second. See
FLOPS. |
|
|
|
| GUI |
(Graphical User Interface)
A graphics-based user interface that incorporates icons, pull-down menus and a mouse. The
GUI has become the standard way users interact with a computer. The major GUIs are the
Windows and Macintosh interfaces, the Motif interface for UNIX and the GNOME and KDE
interfaces for Linux.
The First Commercial GUI Xerox's Star workstation was the first commercial
implementation of the graphical user interface. The Star was introduced in 1981 and was
the inspiration for the Mac and all the other GUIs that followed. (Image courtesy of
Xerox Corporation.) |
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