Lecture Notes CGS1570 - Kbrown, Sum03

Lecture Notes – CGS1570 - KBrown, Sum03

DATA REPRESENTATION

Computers are electronic – need to be able to discern discrete signals of a predefined type (size, intensity, nature) Computers are digital – have discrete elements that can be counted/divided into subsets of discrete sizes All commands, data, flags, interrupts must be discernable in an electronic environment.

Best method is the simplest – ON / OFF - discrete and unambiguous

Two-state system = binary-state system – two conditions can be implemented in many ways: electronic impulse (high/low), magnetic charge (positive/negative), presence or absence of something (on/off)

BIT = binary digit = smallest discernable unit of representation (data) BYTE = grouping of 8 binary digits = to form the basic unit of encoding in microcomputers - can represent a number or part of a number, character, or instruction  Numbers: binary number system, base 2, for calculations  Codes: characters, digits, symbols, special characters o ASCII – American Standard Code for Information Interchange . each is an 8-bit representation of 1 & 0 (uses 128 patterns: 52 alpha, 10 digits, +special characters/punctuation/symbols/codes) . max - 256 unique ordered patterns of 8 bits o Unicode – 16-bit (double byte) character set; based on ASCII code . 256 * 256 = 65,536 patterns possible . international standard for multi-lingual computing  Instructions: commands, flags, interrupts

BINARY NUMBER SYSTEM – (see p 54-58, Computer Confluence)

1024 512 256 128 64 32 16 8 4 2 1 210 29 28 27 26 25 24 23 22 21 20 0 1 0 0 0 1 0 0 0 0 1

example: 01000100001 base2 = 29 + 25 + 20 = (512 + 32 + 1) = 545 base 10

1 binary digit = 1 bit = 1b 8 bits = 1 byte = 1B 1,024 bits = 1 Kilobit = 1Kb 1,024 bytes = 1 Kilobyte = 1KB 1,024 KB = 1 Megabyte = 1MB 1,024 MB = 1 Gigabyte = 1GB 1,024 GB = 1 Terabyte = 1TB

Important distinction: Data = raw data, has no value by itself

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Information = data organized in a meaningful way

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