4.2 Representing Data Electronically

Data is represented in a computer by binary code.

Binary System: the basic data-representation method for computers uses just two numbers: 0 and 1, representing the off/on states of electricity or light pulses.

      

                          

Measuring Capacity

All data and program instructions in the computer are represented as binary.

•Bit: each 0 or 1 is a bit

•Byte: a group of 8 bits = 1 character, digit, or other value

•Kilobyte (KB): 1,000 (1,024) bytes

•Megabyte (MB): 1 million (1,048,576) bytes

•Gigabyte (GB): 1 billion (1,073,741,824) bytes

•Terabyte (TB):  1 trillion (1,009,511,627,776) bytes

•Petabyte (PB):  1 quadrillion bytes

•Exabyte (EB):  1 quintillion bytes

•Binary coding schemes assign a unique binary code to each character.

•ASCII (American Standard Code for Information Interchange)

•Requires 7 or 8 bits per character, depending on the version

•8-bit Extended ASCII provides 256 characters

•Commonly used for microcomputers

•Unicode

•Requires 16 bits per character

•Handles 65,536 characters—used for Chinese and Japanese

•EBCDIC (Extended Binary Coded Decimal Interchange Code)

•Requires 8 bits per character

•Used for IBM mainframes

•Machine Language: The computer’s “native language”

•A binary-type programming language (0s and 1s) built into the CPU that is run directly by the computer.

•Each CPU type has its own machine language; thus each computer’s machine language is brand-dependent.

•Language Translators: The computer’s system software converts higher-level language instructions and data into machine language so that the processor can “understand” what to do.