Online Computer Terms Dictionary - B

bit slice

<architecture> A technique for constructing a processor from modules, each of which processes one bit-field or "slice" of an operand. Bit slice processors usually consist of an ALU of 1, 2, 4 or 8 bits and control lines (including carry or overflow signals usually internal to the CPU). For example, two 4-bit ALUs could be arranged side by side, with control lines between them, to form an 8-bit ALU. A sequencer executes a program to provide data and control signals.

The AMD Am2901 is an example.

(1994-11-15)

bits per inch

<unit> (BPI) A measure of the recording density of a magnetic tape or disk.

(1995-04-13)

bits per pixel

<hardware, graphics> (bpp) The number of bits of information stored per pixel of an image or displayed by a graphics adapter. The more bits there are, the more colours can be represented, but the more memory is required to store or display the image.

A colour can be described by the intensities of red, green and blue (RGB) components. Allowing 8 bits (1 byte) per component (24 bits per pixel) gives 256 levels for each component and over 16 million different colours - more than the human eye can distinguish. Microsoft Windows [and others?] calls this truecolour. An image of 1024x768 with 24 bpp requires over 2 MB of memory.

"High colour" uses 16 bpp (or 15 bpp), 5 bits for blue, 5 bits for red and 6 bits for green. This reduced colour precision gives a slight loss of image quality at a 1/3 saving on memory.

Standard VGA uses a palette of 16 colours (4 bpp), each colour in the palette is 24 bit. Standard SVGA uses a palette of 256 colours (8 bpp).

Some graphics hardware and software support 32-bit colour depths, including an 8-bit "alpha channel" for transparency effects.

(1999-08-01)

bits per second

<communications, unit> (bps, b/s) The unit in which data rate is measured.

For example, a modem's data rate is usually measured in kilobits per second. In 1996, the maximum modem speed for use on the PSTN was 33.6 kbps, rising to 56 kbps in 1997.

Note that kilo- (k), mega- (M), etc. in data rates denote powers of 1000, not 1024.

(2002-03-23)

bit string

<programming, data> An ordered sequence of bits. This is very similar to a bit pattern except that the term "string" suggests an arbitrary length sequence as opposed to a pre-determined length "pattern".

bit stuffing

<protocol> A protocol which guarantees the receiver of synchronous data can recover the sender's clock. When the data stream sent contains a large number of adjacent bits which cause no transition of the signal, the receiver cannot adjust its clock to maintain proper synchronised reception. To eliminate the possibility of such a pathological case, when a preset number of transitionless bits have been transmitted, a bit which does cause a transition is "stuffed" (transmitted) by the sender. The receiver follows the same protocol and removes the stuffed bit after the specified number of transitionless bits, but can use the stuffed bit to recover the sender's clock.

The advantage of bit stuffing is that only a bit (not a byte) is inserted in the data stream, and that only when the content of the data stream fails to provide a timing signal to the receiver. Thus very nearly 100% of the bits transported are useful data. In contrast, asynchronous transmission of data "throws away" a start bit and one or more stop bits for each data byte sent.

(1996-04-23)