Computer users soon become familiar with the use of bits (or more commonly bytes) as a measurement of the capac-ity of computer memory (RAM) and storage devices such as disk drives. They also speak of such things as “16-bit color,” referring to the number of different colors that can be specified and generated by a video display.
In the digital world a bit is the smallest discernable piece of information, representing one of two possible states (indicated by the presence or absence of something such as an electrical charge or magnetism, or by one of two voltage levels). Bit is actually short for “binary digit,” and a bit cor-responds to one digit or place in a binary (base 2) number. Thus an 8-bit value of
11010101
corresponds, from right to left, to (1 * 20) + (0 * 21) + (1 * 22) + (0 * 2 3) + (1 * 24) + (0 * 25) + (1 * 26) + (1 * 27), or 213 in terms of the familiar decimal system.
in terms of bytes. A byte is 8 bits or binary digits, which amounts to a range of from 0 to 255 in terms of decimal (base 10) numbers. A byte is thus enough to store a small inte-ger or a character code in the standard ASCII character set (see character). Common multiples of a byte are a kilobyte (thousand bytes), megabyte (million bytes), gigabyte (billion bytes), and occasionally terabyte (trillion bytes). The actual numbers represented by these designations are actually some-what larger, as indicated in the accompanying table.
With regard to computer architectures the number of bits is particularly relevant to three areas: (1) The size of the basic “chunk” of data or instructions that can be fetched, processed, or stored by the central processing unit (CPU); (2) The “width” of the data bus over which data is sent between the CPU and other devices—given the same processor speed, a 32-bit bus can transfer twice as much data in a given time as a 16-bit bus; and (3) The width of the address bus (now generally 32 bits), which determines how many memory locations can be addressed, and thus the maximum amount of directly usable RAM.
The first PCs used 8-bit or 16-bit processors, while today’s PC processors and operating systems often use 32-bits at a time, with 64-bit processors now entering the mar-ket. Besides the “width” of data transfer, the number of bits can also be used to specify the range of available values. For example, the range of colors that can be displayed by a video card is often expressed as 16 bit (65,536 colors) or 32 bit (16,777,777,216 colors, because only 24 of the bits are used for color information).
Since multiple bits are often needed to specify meaningful information, memory or storage capacity is often expressed.
With regard to computer architectures the number of bits is particularly relevant to three areas: (1) The size of the basic “chunk” of data or instructions that can be fetched, processed, or stored by the central processing unit (CPU); (2) The “width” of the data bus over which data is sent between the CPU and other devices—given the same processor speed, a 32-bit bus can transfer twice as much data in a given time as a 16-bit bus; and (3) The width of the address bus (now generally 32 bits), which determines how many memory locations can be addressed, and thus the maximum amount of directly usable RAM.
The first PCs used 8-bit or 16-bit processors, while today’s PC processors and operating systems often use 32-bits at a time, with 64-bit processors now entering the mar-ket. Besides the “width” of data transfer, the number of bits can also be used to specify the range of available values. For example, the range of colors that can be displayed by a video card is often expressed as 16 bit (65,536 colors) or 32 bit (16,777,777,216 colors, because only 24 of the bits are used for color information).
Since multiple bits are often needed to specify meaningful information, memory or storage capacity is often expressed.
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