Systems Architecture: Chapter 3 Data Representation

double-precision

A data format that combines two adjacent fixed-length data items to hold a single value; increases accuracy or numeric range.

doubly linked list

A data structure in which each list element contains pointers to both the previous and next list elements.

Boolean data type

A data type that can store only the value true or false; requires only a single bit for storage.

excess notation

A format that can be used to represent signed integers with a fixed number of bits; essentially, it divides a range of ordinary binary numbers in half and uses the lower half for negative values and the upper half for nonnegative values

floating point notation

A method for representing real numbers that consists of two parts: a mantissa and an exponent; the mantissa holds the bits that are interpreted to derive the real number's digits, and the exponent value indicates the radix point's position.

flat memory model

An approach to assigning memory addresses in which memory locations are described by single unsigned integers corresponding to linear positions

multinational characters

Modified Latin characters, such as Ç and ã, used by Western European languages other than English.

numeric range

The set of all data values that can be represented by a data-encoding method.

octal notation

a base-8 numbering system that uses digits from 0 to 7.

underflow

a condition that occurs when a value is too small to represent in floating point notation; also refers to overflow of a negative exponent in floating-point notation

pointer

a data element containing the address of another data element; typically used in data structures.

record

a data structure composed of other data structures or primitive data elements; commonly used as a unit of input and output to and from files or databases.

class

a data structure containing both traditional (static) data elements and programs that manipulate data; it combines related data items in much the same way a record does, but it extends a record to include methods for manipulating data items.

singly linked list

a data structure in which each list element contains a pointer to the next list element

linked list

a data structure that uses pointers so that list elements can be scattered among non-sequential storage locations

unsigned integer

a data type that stores positive integer values as ordinary binary numbers; its value is always assumed to be positive.

Boolean Logic

a formal logic system in which statements can be evaluated only as true or false; well suited to the binary numbers used in computer processing

bit string

a group of bits describing a single data value

base or radix

a multiplier that describes the difference between one position and the next in a numbering system.

twos complement notation

a notation system that represents positive integers as ordinary binary values and negative integers by adding 1 to the complement of the positive value

binary number

a number in which each digit can have only one of two possible values (0 or 1).

real number

a number that can contain both whole and fractional components; the fractional portion is represented by digits to the right of the radix point.

hexadecimal notation

a numbering system with a base value of 16; uses digits from 0 and 9 and letters A to F; which represent the decimal values 10 to 15.

data structure

a related group of primitive data elements organized for some type of common processing; it's defined and manipulated in software because the CPU can't manipulate data structures directly.

string

a sequence of characters forming a meaningful word, phrase, or other useful group.

file

a sequence of records on secondary storage; the common organization schemes for files are sequential and indexed.

Unicode

a standard 16-bit or 32-bit character-coding method that assigns non-negative integers to represent printable characters; includes alphabets, ideographs, and characters for most of the world's languages.

American Standard Code for Information Interchange (ASCII)

a standard 7-bit coding method for character data and some device control codes.

byte

a string of 8 bits; generally the smallest unit of data that can be read from or written to a storage device.

character

a symbol in a written language, including letters, numerals, and punctuation marks.

Extended Binary Coded Decimal Interchange Code (EBCDIC)

an IBM mainframe coding method for representing character data in an 8-bit format.

Latin-1

an ISO standard character coding table containing the ASCII-7 characters in the lower 128 table entries and most of the characters used by Western European languages in the upper 128 table entries

segmented memory model

an approach to assigning memory addresses in which primary storage is divided into equal sized segments called pages, identified by sequential nonnegative integers; each byte of memory has a two part address: the first part identifies the page, the second part identifies the byte in the page

overflow

an error that occurs when the result of a processing operation exceeds the format's numeric range

signed integer

an integer that uses a sign bit to indicate whether the value is negative or positive

International Organization for Standardization (ISO)

an international group with functions similar to those of the American National Standards Institute.

array

an ordered list of data elements, in which each element can be referenced by an index to its position; array elements are normally referenced by the array name and the index value.

bit

derived from the term binary digit, it represents one digit of a binary number and can have the value 0 or 1.

long integers

double-precision representations of integers.

manipulation

in computer processing, refers to working with data by executing processor instructions, such as addition, subtraction, and equality comparisons.

index

in file organization, an array of pointers to records.

integer

is a whole number -- a value that doesn't have a fractional part.

object

one instance, or variable, of a class

methods

programs for manipulating data items in a class.

truncation

the act of deleting bits that don't fit in a storage location.

primitive data types or machine data types

the integer, real number, character, Boolean, and memory address data types that CPU's can manipulate directly.

International Alphabet 5 (IA5)

the international equivalent of the ASCII coding method for character data

most significant digit or high-order bit

the leftmost digit in a bit string the represents the greatest weight.

address

the location of a data element in a storage device; often used in data structures

decimal point or radix point

the period or comma in the decimal numbering system that separates the whole and fractional parts of a numeric value.

least significant digit or low-order bit

the rightmost digit in a bit string that represents the lowest weight.

collating sequence

the specific order for assigning numeric codes to characters or symbols.