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Baud is rate, the signalling rate of a line, the switching speed, or the number of transitions (voltage or frequency changes) that are made per second. Transmission speeds are often expressed in baud, though bits per second (bps) is more accurate. The speed at which your computer talks to your modem.
Short for binary digit, the smallest unit of information on a machine. The term was first used in 1946 by John Tukey, a leading statistician and adviser to five presidents. A single bit can hold only one of two values: 0 or 1. More meaningful information is obtained by combining consecutive bits into larger units. For example, a byte is composed of 8 consecutive bits.
Computers are sometimes classified by the number of bits they can process at one time or by the number of bits they use to represent addresses. These two values are not always the same, which leads to confusion. For example, classifying a computer as a 32-bit machine might mean that its data registers are 32 bits wide or that it uses 32 bits to identify each address in memory. Whereas larger registers make a computer faster, using more bits for addresses enables a machine to support larger programs.
Graphics are also often described by the number of bits used to represent each dot. A 1-bit image is monochrome; an 8-bit image supports 256 colors or grayscales; and a 24- or 32-bit graphic supports true color.
Abbreviation of bits per second, the standard measure of data transmission speeds.
Bps differs from baud when more than one bit is represented by a single cycle of the carrier.
Abbreviation for binary term, a unit of storage capable of holding a single character. On almost all modern computers, a byte is equal to 8 bits. Large amounts of memory are indicated in terms of kilobytes (1,024 bytes), megabytes (1,048,576 bytes), and gigabytes (1,073,741,824 bytes). A disk that can hold 1.44 megabytes, for example, is capable of storing approximately 1.4 million characters, or about 3,000 pages of information.
The speed with which data can be transmitted from one device to another. Data rates are often measured in megabits (million bits) or megabytes (million bytes) per second. These are usually abbreviated as Mbps and MBps, respectively.
Another term for data transfer rate is throughput.
(1) 2 to the 60th power (1,152,921,504,606,846,976) bytes. An exabyte is equal to 1,024 petabytes.
(2) When capitalized, the name of a manufacturer of mass storage devices.
Short for Gigabits per second, a data transfer speed measurement for high-speed networks such as Gigabit Ethernet. When used to describe data transfer rates, a gigabit equals 1,000,000,000 bits.
2 to the 30th power (1,073,741,824) bytes. One gigabyte is equal to 1,024 megabytes. Gigabyte is often abbreviated as G or GB.
Short for kilobits per second, a measure of data transfer speed. Modems, for example, are measured in Kbps. Note that one Kbps is 1,000 bits per second, whereas a KB (kilobyte) is 1,024 bytes. Data transfer rates are measured using the decimal meaning of K whereas data storage is measured using the powers-of-2 meaning of K. Technically, kbps should be spelled with a lowercase k to indicate that it is decimal but almost everyone spells it with a capital K.
1,024 bits for technical purposes, such as data storage. 1,000 for general purposes. Data transfer rates are measured in kilobits per second, abbreviated as Kbps, and count a kilo as 1,000 bits.
In decimal systems, kilo stands for 1,000, but in binary systems, a kilo is 1,024 (2 to the 10th power). Technically, therefore, a kilobyte is 1,024 bytes, but it is often used loosely as a synonym for 1,000 bytes. For example, a computer that has 256K main memory can store approximately 256,000 bytes (or characters) in memory at one time.
A megabyte is 2 to the 20th power (approximately 1 million) and a gigabyte is 2 to the 30th power (approximately 1 billion).
In computer literature, kilobyte is usually abbreviated as K or Kb. To distinguish between a decimal K (1,000) and a binary K (1,024), the IEEE has suggested following the convention of using a small k for a decimal kilo and a capital K for a binary kilo, but this convention is by no means strictly followed.
Refers to various techniques and devices for storing large amounts of data. The earliest storage devices were punched paper cards, which were used as early as 1804 to control silk-weaving looms. Modern mass storage devices include all types of disk drives and tape drives. Mass storage is distinct from memory, which refers to temporary storage areas within the computer. Unlike main memory, mass storage devices retain data even when the computer is turned off.
The main types of mass storage are:
- floppy disks : Relatively slow and have a small capacity, but they are portable, inexpensive, and universal.
- hard disks : Very fast and with more capacity than floppy disks, but also more expensive. Some hard disk systems are portable (removable cartridges), but most are not.
- optical disks : Unlike floppy and hard disks, which use electromagnetism to encode data, optical disk systems use a laser to read and write data. Optical disks have very large storage capacity, but they are not as fast as hard disks. In addition, the inexpensive optical disk drives are read-only. Read/write varieties are expensive.
- tapes : Relatively inexpensive and can have very large storage capacities, but they do not permit random access of data.
Mass storage is measured in kilobytes (1,024 bytes), megabytes (1,024 kilobytes), gigabytes (1,024 megabytes) and terabytes (1,024 gigabytes).
Mass storage is sometimes called auxiliary storage.
Short for megabits per second, a measure of data transfer speed. Networks, for example, are generally measured in Mbps.
(1) When used to describe data storage, 1,024 kilobits.
(2) When used to described data transfer rates, it refers to one million bits. Networks are often measured in megabits per second, abbreviated as Mbps.
(1) When used to describe data storage, 1,048,576 (2 to the 20th power) bytes. Megabyte is frequently abbreviated as M or MB.
(2) When used to describe data transfer rates, as in MBps, it refers to one million bytes.
Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk.
Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information.
There are several different types of memory:
- RAM (random-access memory) : This is the same as main memory. When used by itself, the term RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.
- ROM (read-only memory) : Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to.
- PROM (programmable read-only memory) : A PROM is a memory chip on which you can store a program. But once the PROM has been used, you cannot wipe it clean and use it to store something else. Like ROMs, PROMs are non-volatile.
- EPROM (erasable programmable read-only memory) : An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light.
- EEPROM (electrically erasable programmable read-only memory) : An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge.
Acronym for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over telephone lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.
Fortunately, there is one standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have. There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems.
While the modem interfaces are standardized, a number of different protocols for formatting data to be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, while others have been developed by private companies. Most modems have built-in support for the more common protocols -- at slow data transmission speeds at least, most modems can communicate with each other. At high transmission speeds, however, the protocols are less standardized.
Aside from the transmission protocols that they support, the following characteristics distinguish one modem from another:
- bps : How fast the modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 57,600 bps, although they can achieve even higher data transfer rates by compressing the data. Obviously, the faster the transmission rate, the faster you can send and receive data. Note, however, that you cannot receive data any faster than it is being sent. If, for example, the device sending data to your computer is sending it at 2,400 bps, you must receive it at 2,400 bps. It does not always pay, therefore, to have a very fast modem. In addition, some telephone lines are unable to transmit data reliably at very high rates.
- voice/data : Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication.
- auto-answer : An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use.
- data compression : Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique.
- flash memory : Some modems come with flash memory rather than conventional ROM, which means that the communications protocols can be easily updated if necessary.
- Fax capability : Most modern modems are fax modems, which means that they can send and receive faxes.
To get the most out of a modem, you should have a communications software package, a program that simplifies the task of transferring data.
Communications Protocols :
Maximum Transmission Rate
Bell 103 300 bps Full CCITT V.21 300 bps Full Bell 212A 1,200 bps Full ITU V.22 1,200 bps Half ITU V.22bis 2,400 bps Full ITU V.29 9,600 bps Half ITU V.32 9,600 bps Full ITU V.32bis 14,400 bps Full ITU V.34 36,600 bps Full ITU V.90 56,000 bps Full
2 to the 50th power (1,125,899,906,842,624) bytes. A petabyte is equal to 1,024 terabytes.
(1) The capacity of a device to hold and retain data.
(2) Short for mass storage.
(1) 2 to the 40th power (1,099,511,627,776) bytes. This is approximately 1 trillion bytes.
(2) 10 to the 12th power (1,000,000,000,000). This is exactly one trillion.
The amount of data transferred from one place to another or processed in a specified amount of time. Data transfer rates for disk drives and networks are measured in terms of throughput. Typically, throughputs are measured in Kbps, Mbps and Gbps.
2 to the 80th power bytes, which is approximately 10 to the 24th power (1,000,000,000,000,000,000,000,000) bytes. A yottabyte is equal to 1,024 zettabytes.
The name yotta was chosen because it's the second-to-last last letter of the Latin alphabet and also sounds like the Greek letter iota.
2 to the 70th power bytes, which is approximately 10 to the 21st power (1,000,000,000,000,000,000,000) bytes. A zettabyte is equal to 1,024 exabytes.
The name zetta was chosen because it's the last letter of the Latin alphabet and also sounds like the Greek letter Zeta.
Sources: Various books, the Internet, and various encyclopedias.
Kilder: Forskellige bøger, internettet og forskellige leksikoner.