Bauds, Bits and Bytes. The basics to understanding telecommunication systems.
A bit is an abbreviation for binary digit, which is the smallest unit of information in a
computer. A bit is represented by the number 1 or the number 0, which corresponds to the
states on or off, true or false, and yes or no.
The term bit was first introduced by John Turkey, an American statistician and early
computer scientist, who used the term in 1946 as a shortened form of binary digit.
Bits are the basis for all information processing that goes on in digital electronics and
computer. They actually represent the state of a transistor in the switching and timing
circuits in the computer. The number 1 (meaning on, yes or true) is used to represent a
transistor with current flowing through it (a closed circuit), while the number 0 (meaning
off, no or false) is used to represent a transistor with no current flowing through it (an
open circuit). All computer information processing can be understood in terms of vast
arrays of transistors (3.1 million transistors on the Pentium Chip) switching on and off,
depending on the bit value they have been assigned.
The value of a bit is usually stored as either above or below a designated level of
electrical charge in a single capacitor within a memory device. Every digit in a binary
number is referred to as a bit and represents a power of two. For example, in the binary
number 101, the 1 at the right represents 1 x 2º; the 0 in the middle represents 0 x 2¹;
and the 1 to the far left represents 1 x 2². The decimal equivalent of 101 is (1 x 2²) +
(0 x 2¹) + (1 x 2º) = 4 + 0 + 1 = 5.
Computers are often classified by the number of bits they can process at a time, as well
as by the number of bits used to represent pixels (short for picture elements), the
smallest identifiable parts of an image. In monochrome images, each pixel is made up of at
least 24 bits. Bits are usually combined into larger units called bytes.
A byte is usually composed of 8 bits, although 16 bits are also used. The term byte was
first used in 1956 by computer scientist Werner Buchholz to prevent confusion with the
word bit. He described byte as a group of bits used to encode a character. The eight-bit
byte was created that year and was soon adopted by the computer industry as a standard. In
some systems, the term octet is used for an eight-bit unit instead of byte. Half
a byte (four bits) is called a nibble.
The values that a byte can take on range from 00000000 (0 in decimal notation) and
11111111(225 in decimal notation). This means that a byte can represent 2 to the power of
8 or 256 possible states (0-255). Bytes are combined into groups of 1-8 bytes called
words. The size of the words used by a computer's Central Processing Unit depends on the
bit-processing ability of the CPU. For example, in many systems (32-bit systems), four
eight-bit bytes or octets form a 32-bit word. In such systems, instruction lengths are sometimes
expressed as full-word (32 bits in length) or half-word (16 bits in length).
The particular sequence of bits in the byte encodes a unit of information such as a
keyboard character. One byte represents a single character such as a number
("5"), a letter ("A") or a typographic symbol ("?"). For
example, the letter "A" is represented in a byte as 01000001. Most computers
operate by manipulating groups of 2, 4, or 8 bytes (words).
Software designers use computer and software to combine bytes in complex ways and create
meaningful data in the form of text files or binary files (files that contain data to be
processed and interpreted by a computer). Bits and bytes are the basis for creating all
meaningful information and programs on computers. For example, bits form bytes, which
represent characters and can be combined to form words, sentences, paragraphs, and
eventually, entire documents.
Bytes are also the key unit for measuring quantity of data. Data quantity is commonly
measured in kilobytes (KB - 1024 bytes), megabytes (MB - 1,048,576 bytes) or gigabytes
(about 1 billion bytes). A regular floppy disk usually holds 1.44 MB of disk-space, which
is equal to about 1,400,000 keyboard characters among other types of data. At this storage
capacity, a single disk can hold a document approximately 700 pages long, with 2000
characters per page.
Storage is measured in bytes, while transmission capacity is measured in bits per second.
A 28.8 Kbps modem is one that operates at 28.8 thousand bits per second.
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Baud was the prevalent measure for data transmission speed until replaced by a more
accurate term, bps (bits per second). The term baud was named after a
French engineer, Jean-Maurice-Emile Baudot, and was first used to measure the speed of
Baud rate is commonly a reference to the speed at which a modem can transmit data. It is
often incorrectly assumed that Baud indicates the number of bits per second transmitted.
It actually measures the number of events, or electronic state changes that occur in 1
second. Since a single state change can involve more than a single bit of data in
high-speed digital communications, the bps unit of measurement has replaced it as a better
expression of data transmission speed.
For example, a so-called 9600-baud modem that encodes 4 bits per event actually operates
at 2400 baud, but transmits 9600 bits per second (2400 events times 4 bits per event) and
thus should be called a 9600bps modem.