What Is 64 Bits

[Carlito Roby]

Abit (binary digit) is the smallest unit of data that a computer can process and store. A bit is always in one of two physical states, similar to an on/off light switch. The state is represented by a single binary value, usually a 0 or 1. However, the state might also be represented by yes/no, on/off or true/false. Bits are stored in memory through the use of capacitors that hold electrical charges. The charge determines the state of each bit, which, in turn, determines the bit's value.

Although a computer might be able to test and manipulate data at the bit level, most systems process and store data in bytes. A byte is a sequence of eight bits that are treated as a single unit. References to a computer's memory and storage are always in terms of bytes. For example, a storage device might be able to store 1 terabyte (TB) of data, which is equal to 1,000,000 megabytes (MB). To bring this into perspective, 1 MB equals 1 million bytes, or 8 million bits. That means a 1 TB drive can store 8 trillion bits of data.

Each bit in a byte is assigned a specific value, which is referred to as the place value. A byte's place values are used to determine the meaning of the byte as a whole, based on the individual bits. In other words, the byte values indicate what character is associated with that byte.

The place values are used in conjunction with the bit values to arrive at the byte's overall meaning. To calculate this value, the place values associated with each 1 bit are added together. This total corresponds to a character in the applicable character set. A single byte can support up to 256 unique characters, starting with the 00000000 byte and ending with the 11111111 byte. The various combinations of bit patterns provide a range of 0 to 255, which means that each byte can support up to 256 unique bit patterns.

For example, the uppercase "S" in the American Standard Code for Information Interchange (ASCII) character set is assigned the decimal value of 83, which is equivalent to the binary value of 01010011. This figure shows the letter "S" byte and the corresponding place values.

The "S" byte includes four 1 bits and four 0 bits. When added together, the place values associated with 1 bits total 83, which corresponds to the decimal value assigned to the ASCII uppercase "S" character. The place values associated with the 0 bits are not added into the byte total.

Because a single byte supports only 256 unique characters, some character sets use multiple bytes per character. For example, Unicode Transformation Format character sets use between 1 and 4 bytes per character, depending on the specific character and character set. Despite these differences, however, all character sets rely on the convention of 8 bits per byte, with each bit in either a 1 or 0 state.

The term octet is sometimes used instead of byte, and the term nibble is occasionally used when referring to a 4-bit unit, although it's not as common as it once was. In addition, the term word is often used to describe two or more consecutive bytes. A word is usually 16, 32 or 64 bits long.

The relation between these values and the physical states of the underlying storage or device is a matter of convention, and different assignments may be used even within the same device or program. It may be physically implemented with a two-state device.

A contiguous group of binary digits is commonly called a bit string, a bit vector, or a single-dimensional (or multi-dimensional) bit array.A group of eight bits is called one byte, but historically the size of the byte is not strictly defined.[2] Frequently, half, full, double and quadruple words consist of a number of bytes which is a low power of two. A string of four bits is usually a nibble.

In information theory, one bit is the information entropy of a random binary variable that is 0 or 1 with equal probability,[3] or the information that is gained when the value of such a variable becomes known.[4][5] As a unit of information, the bit is also known as a shannon,[6] named after Claude E. Shannon.

The symbol for the binary digit is either "bit", per the IEC 80000-13:2008 standard, or the lowercase character "b", per the IEEE 1541-2002 standard. Use of the latter may create confusion with the capital "B" which is the international standard symbol for the byte.

The encoding of data by discrete bits was used in the punched cards invented by Basile Bouchon and Jean-Baptiste Falcon (1732), developed by Joseph Marie Jacquard (1804), and later adopted by Semyon Korsakov, Charles Babbage, Herman Hollerith, and early computer manufacturers like IBM. A variant of that idea was the perforated paper tape. In all those systems, the medium (card or tape) conceptually carried an array of hole positions; each position could be either punched through or not, thus carrying one bit of information. The encoding of text by bits was also used in Morse code (1844) and early digital communications machines such as teletypes and stock ticker machines (1870).

Ralph Hartley suggested the use of a logarithmic measure of information in 1928.[7] Claude E. Shannon first used the word "bit" in his seminal 1948 paper "A Mathematical Theory of Communication".[8][9][10] He attributed its origin to John W. Tukey, who had written a Bell Labs memo on 9 January 1947 in which he contracted "binary information digit" to simply "bit".[8]

A bit can be stored by a digital device or other physical system that exists in either of two possible distinct states. These may be the two stable states of a flip-flop, two positions of an electrical switch, two distinct voltage or current levels allowed by a circuit, two distinct levels of light intensity, two directions of magnetization or polarization, the orientation of reversible double stranded DNA, etc.

Bits are transmitted one at a time in serial transmission, and by a multiple number of bits in parallel transmission. A bitwise operation optionally processes bits one at a time. Data transfer rates are usually measured in decimal SI multiples of the unit bit per second (bit/s), such as kbit/s.

In the earliest non-electronic information processing devices, such as Jacquard's loom or Babbage's Analytical Engine, a bit was often stored as the position of a mechanical lever or gear, or the presence or absence of a hole at a specific point of a paper card or tape. The first electrical devices for discrete logic (such as elevator and traffic light control circuits, telephone switches, and Konrad Zuse's computer) represented bits as the states of electrical relays which could be either "open" or "closed". When relays were replaced by vacuum tubes, starting in the 1940s, computer builders experimented with a variety of storage methods, such as pressure pulses traveling down a mercury delay line, charges stored on the inside surface of a cathode-ray tube, or opaque spots printed on glass discs by photolithographic techniques.

In the 1950s and 1960s, these methods were largely supplanted by magnetic storage devices such as magnetic-core memory, magnetic tapes, drums, and disks, where a bit was represented by the polarity of magnetization of a certain area of a ferromagnetic film, or by a change in polarity from one direction to the other. The same principle was later used in the magnetic bubble memory developed in the 1980s, and is still found in various magnetic strip items such as metro tickets and some credit cards.

In modern semiconductor memory, such as dynamic random-access memory, the two values of a bit may be represented by two levels of electric charge stored in a capacitor. In certain types of programmable logic arrays and read-only memory, a bit may be represented by the presence or absence of a conducting path at a certain point of a circuit. In optical discs, a bit is encoded as the presence or absence of a microscopic pit on a reflective surface. In one-dimensional bar codes, bits are encoded as the thickness of alternating black and white lines.

The bit is not defined in the International System of Units (SI). However, the International Electrotechnical Commission issued standard IEC 60027, which specifies that the symbol for binary digit should be 'bit', and this should be used in all multiples, such as 'kbit', for kilobit.[11] However, the lower-case letter 'b' is widely used as well and was recommended by the IEEE 1541 Standard (2002). In contrast, the upper case letter 'B' is the standard and customary symbol for byte.

Multiple bits may be expressed and represented in several ways. For convenience of representing commonly reoccurring groups of bits in information technology, several units of information have traditionally been used. The most common is the unit byte, coined by Werner Buchholz in June 1956, which historically was used to represent the group of bits used to encode a single character of text (until UTF-8 multibyte encoding took over) in a computer[2][12][13][14][15] and for this reason it was used as the basic addressable element in many computer architectures. The trend in hardware design converged on the most common implementation of using eight bits per byte, as it is widely used today.[as of?] However, because of the ambiguity of relying on the underlying hardware design, the unit octet was defined to explicitly denote a sequence of eight bits.

Computers usually manipulate bits in groups of a fixed size, conventionally named "words". Like the byte, the number of bits in a word also varies with the hardware design, and is typically between 8 and 80 bits, or even more in some specialized computers. In the 21st century, retail personal or server computers have a word size of 32 or 64 bits.

The International System of Units defines a series of decimal prefixes for multiples of standardized units which are commonly also used with the bit and the byte. The prefixes kilo (103) through yotta (1024) increment by multiples of one thousand, and the corresponding units are the kilobit (kbit) through the yottabit (Ybit).

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