Computer Science IBHL - ALL Vocabulary
B
- Byte - 1 Byte = 8 bits, values from 0 to 255
De Morgan's law
- If A and B are Boolean expressions, then not (A and B) = (not A) or (not B) not(A or B) = (not A) and (not B) - ex: It's not (Sat or Sun) = not Sat AND not Sun; I'm not big and handsome = either I'm not big or I'm not handsome
disk cache
- RAM set aside to speed up access to a hard drive; this may be part of the disk itself or may be incorporated in cache memory - ex: typically 8 or 16 Megabytes
collection
- a class designed to hold objects (referred to in the syllabus as data structure)
database management system (DBMS)
- a computer-based system for defining, creating, manipulating, controlling, managing and using databases - ex: MySQL, MS-Access, Oracle
data member
- a data type that is a member of a class - ex: variables, arrays, objects inside a class
check digit
- a digit added to numerical data that can be recalculated and hence used to check data integrity after input, transmission and so on - ex: credit card numbers, ISBN book number
digital signature
- a digital code attached to an electronic message or document, which is unique and which can be used to authenticate the sender or owner - most often used in electronic commerce - ex: in the Internet, a large data file encrypted using a password and Public Key algorithm; could also use simpler password technology in a private network (e.g. E-banking)
fully-indexed file
- a file in which, although the records are unordered, a particular record can be found using a sequential access to the index of the file followed by direct access to the data file - ex: a telephone list is fully indexed, has an entry for each person, but could reference a more detailed file with more data; NOT a partially indexed file, with sections for each letter, or the index of a book which only contains some of the words
direct access file
- a file organized in such a way that a calculation provides the address (location) of a record so that the record can be accessed directly. The records in the file may be ordered or unordered - ex: usually large databases, such as a telephone directory for an entire country, or a database containing airline reservations; direct access makes fast access possible, which is especially important in large databases
character set
- a finite set of different characters that is complete for a given purpose, for example, the 128 ASCII characters - ex: ISO (Windows normal), System, Wing-Dings; extended characters (ASCII 128-255) are Foreign letters, may have different codes in different character set MAPPINGS
doubly linked list
- a linked list in which each node has both a head pointer and a tail pointer - ex: a line of kids holding hands - each kid is connect to both the kid before and the kid after; if used to track disk-drive sector allocation, it is possible to reconstruct the list even if one link gets broken
batch processing
- a method of processing data in which transactions are collected and prepared for input to the computer for processing as a single unit, for example, payroll - ex: recording all the SALES in a store for one day into a MASTER file; converting lots of graphics files to the same format; without loading and saving them one at a time.
data compression
- a method of reducing the size of data. All redundancy in the data is removed to reduce the storage needed or to speed up transfer - the data can be uncompressed back to its original state - ex: WinZip is a compression utility, which implements the Zip algorithm; .GIF uses LOSSLESS compression, JPEG is LOSSY (removes some details); videos use delta compression, starting with a "keyframe", and after that transmitting only the DIFFERENCES (changes) between frames
constructor method
- a method with the same name as the class that initializes the instance variables of an object of the class when the object is instantiated
client-server
- a network architecture in which a system is divided between server tasks performed on the instructions received from clients, requesting information - ex: client sends print-job to a print-server, client stores data files on the server, web client downloads pages from a Web server
bus ology
- a network in which all devices are connected to a common cable, known as the "bus" - ex: commonly uses coaxial cable and Ethernet protocol; sensible for a small office with only a few work-stations
distributed processing
- a network in which some or all of the processing, storage and control functions, in addition to input/output functions, are dispersed among its nodes - ex: SETI has a screen saver that analyses sets of radio data on millions of PCs connected to the Internet.; the PC analyses the data, and sends it's results back to a central server
BigO notation
- a notation used to describe the relative performance (speed) of an algorithm - ex: Bubble Sort is O(n^2), Binary Search is O(ln n), Merge is O(n)
arithmetic and logic unit (ALU)
- a part of the computer that performs arithmetic operations, logic operations and related operations - ALU contains Registers and circuits for arithmetic and logic - ALU does NOT contain circuits for sending addresses and data and from RAM
ALU
- a part of the computer that performs arithmetic operations, logic operations and related operations - examples: speed measured in Flops (Floating Point Operations per Second)
bar code
- a pattern of vertical lines distinguished from each other by width - It can be read by a bar code reader to provide data to a computer - ex: on cans in the grocery store, books in the library
buffer
- a portion of storage used to hold input or output data temporarily - ex: printer receives an entire page, stores it, then prints it; Web video - several second are "cached" before display starts; CD burner buffers output before writing to avoid a buffer under-run
exception handler
- a program code that handles exceptions that arise during the running of a program; an exception is thrown to the handler rather than causing a fatal error - ex: in Java, use try...catch...to handle exceptions
applet (Java)
- a program that runs in the context of a browser - examples: simple web-games, web-page menu system, price-calculator
application (Java)
- a program that runs when translated by a Java compiler - examples: Open Office, open-source projects, IB dossiers
compiler
- a program that translates a source program into machine code that can be converted into an executable program (an object program) - C++, Visual Basic, Pascal-most High Level Languages - ex: Java uses a compiler to produce p-code, which must run in an interpreter, so the Java compiler does not produce "machine code"; NOT Java-script, which runs directly in an interpreter
debugging tool
- a program used to detect, trace and eliminate errors in computer programs or other software - can pause a program in the middle and allow the programmer to investigate the contents of important variables
circular queue
- a queue in which the storage area is fixed (e.g. array) and the first item is held in a location that is logically next to the storage location for the last item of the queue - data items can be thought of as being arranged in a circle - ex: keyboard queue in a PC; like days of the week (repeat in a cycle), an array where you go back to the beginning once you reach the end
binary search
- a search in which, at each step of the search, the set of data elements is divided by two, until the searched element is found - ex: Search for "CAR" in {"BIKE", "CAR", "JEEP","TRUCK","WAGON"} Search("CAR",0,4) → Mid = (0+4) / 2 = 3 → JEEP? → CAR is smaller Search("CAR",0,1) → Mid = (0+1) div 2 = 0 → BIKE? → CAR is bigger Search("CAR",1,1) → Mid = (1+1) div2 = 1 → CAR ? → Yes, found
back-up (file)
- a second copy of a file, to be used in the event of the original file being corrupted - ex: an automatic .BAK copy of a document made by MSWord; a copy of all student's grades stored on a backup tape; an "image" of an antire hard-disk, stored on a CD-R
computer program
- a sequence of instructions suitable for processing by a computer - ex: Java application, C++ program (video game), Microsoft Word, Internet Explorer - NOT a document, web-page, or database
expression
- a sequence of symbols that can be evaluated - ex: (3*x - 4/y) is a numeric expression; (LastName + ", " + FirstName) is a string expression; ( (age >= 21) and (country.equals("France") ) ) is a Boolean expression
Byte (B)
- a set of bits considered as a unit - it normally consists of 8 bits and corresponds to a single character of information ex: 1 Byte = 8 bits, values from 0 to 255
command language
- a set of procedural operators with a related syntax, used to indicate the functions to be performed by an operating system - ex: In DOS, you can write a BATCH FILE to perform backups: COPY "*.DOC A:\" or to clean up all the useless files: DEL "*.tmp /s" - the commands COPY and DELETE are part of the command language - this is NOT a general-purpose programming language - it does not provide variables, procedures, or input/output functions.
clash (collision)
- a situation in which two or more entries in a file or other data structure are given the same memory location through the use of a hash table - In a HashTable, when two pieces of data belong in the same place (same hash key) - ex: locker numbers might be computed from the student's name: Jones gets J = 10, o = 15 → 10*26 + 15 = 235, then Johnson and Jones would get the same locker
bubble sort
- a sort in which the first two items to be sorted are examined and exchanged if necessary to place them in the specified order; the second item is then compared with the third (exchanging them if required), the third is compared with the fourth, and the process is repeated until all pairs have been examined and all items are in the proper sequence - ex: for (int pass = 0; pass < data.length; pass = pass + 1 ) { for (int c = 0; c < data.length - 1; c = c + 1 ) { if (data[c] > data[c+1]) int temp = data[c]; data[c] = data[c+1]; data[c+1] = temp; } } - this example is "inefficient": an efficient algorithm would sort after a pass with no swaps
accumulator
- a storage register in the ALU that holds data temporarily while the data is processed and before it is transferred to memory - examples: Old Intel 8086 chips had AX, BX, CX, DX as 16-bit registers; Add AX, BX --> like AX = AX + BX in Java
field (object attribute)
- a subdivision of a record containing a unit of information - ex: a payroll record might have the following fields: clock number, gross pay, deductions and net pay - this class contains two fields: class Fraction { int numerator; int denominator; }
check sum
- a sum generated using individual digits of a number and employed as an error-detecting device - ex: Internet Packets contain a check sum, the sum of all bytes in the packet
binary tree
- a tree in which each node has at most two children
balanced tree
- a tree in which the right and left subtrees of any node have heights differing by one at the most - ex: With 7, 15, 31 ... 2^n - 1 elements, the tree can be PERFECTLY balanced - Otherwise, there may be a few branches which are 1 element longer. So this tree is balanced, but not perfectly symmetrical: +--> Stevens +--> Moore | +--> Lewis | +--> King | Kelly | + --> Irving | +--> HAL | | +--> Dave +--> Babbage +--> Adams
argument
- a value or object passed to a method when it is called - examples: usually a number in a function, e.g. sin(60) --> 60 is the argument
abstract data structure
- a way of organizing data and its related procedures and functions - also called Abstract Data Type (ADT) - examples: Queue, Stack, Linked-List, Tree
DMA
- access to memory and devices without the direct control of the processor; this is most often used for hard disk access and screen display - ex: a disk-drive reads and writes directly to/from RAM, rather than sending the data through the CPU. Graphics cards can also use DMA and bypass the CPU; some cheap systems actually use the main memory RAM to store the graphics data, so there is no graphics card in the system - this is cheap but slow and not good for games
file manager
- an application software that can access, create, modify, store and retrieve files - ex: Windows Explorer, when you see the directory tree and can copy and paste files
defragmentation software
- an application that reads file segments from non-contiguous sections of a storage device and then writes the files to the same device in such a way that each file segment is contiguous - ex: defrag in Windows - there are also 3rd party tools
array
- an arrangement of data in one or more dimensions - in programming languages, an aggregate that consists of data objects, with identical attributes, each of which may be uniquely referenced by indexing - examples: String[] days = {"Sun","Mon","Tue","Wed","Thu","Fri","Sat"}; String[][] ticTacToe = new String[3][3]
Boolean expression
- an expression that has a value of True (T) or False (F) - ex: if ( (Age >= 18) and (nation.equals("US") )
BMP
- an extension given to files in bitmap form - ex: it's NOT a Web format, it's NOT compressed, uses RGB with 3 bytes per pixel
flag
- an indicator with two possible states, "set" or "not set", that can be represented by one bit - can be used to indicate that a record can be deleted, to indicate end of input/output and to sense whether an interrupt has occurred - ex: found = false // a boolean flag loop through array if String matches target found = true end loop return found
exception
- an object that is created when an abnormal situation arises in a program - ex: IOException - an error caused when a file is missing or disk is full
binary operator
- an operator that combines two operands to give a single result, for example, addition, multiplication, division, mod, div. - ex: subtraction: 8 - 2, Concatenation: firstName + lastName; NOT sqrt(100) → sqrt is a UNARY operator, has 1 operand
bar code reader
- an optical reader that can read bar codes - at cashier in the grocery store
algorithm
- an ordered set of well-defined instructions for the solution of a problem in a finite number of steps - examples: bubble-sort, binary search, merge sorted lists
file
- an organized collection of data - ex: program source code (game.java), executable (game.exe), document (game.doc), graphics file (screenshot.jpg), web-page (index.html)
A-D converter
- analog-digital converter - a device for converting analog signals into digital ones for subsequent computer processing; sometimes called a "digitizer" - a digital to analog (D to A) converter operates in the reverse direction - examples: sound card, scanner, digital camera, thermal sensor
bit (b)
- binary digit - the smallest unit of information for data storage and transmission - each bit is considered to be either a "0" or a "1" - ex: could be a TRANSISTOR, a LIGHT (LED), a PIXEL (black or white)
bps
- bits per second. - ex: 56 K Modem → 56000 bits per second, ADSL = 1 - 16 MegaBits per sec
fibre optic
- cabling used for networking that uses fine strands of glass - the medium can carry a great deal of data and it gives a fast transfer rate - ex: internet backbone, connections between servers in a server farm
CRC cards
- class, responsibility, collaboration cards - a design tool for classes that lists a class's name, its responsibilities and the classes with which it collaborates on an index card
class
- combination of data and operations that can be performed on that data; specification of the data members and methods of the object - in Java, every program is a Class - when you make a NEW object, it is a copy of a Class
cylinder
- concentric disk tracks of a hard disk (one on of the other) form a cylinder - with 2 platters, a cylinder consists of 4 tracks, one on each side of each disk
formatted output
- data prepared for output in order to be displayed in a desired format (for example, trailing zero on 7.50$ instead of 7.5$) - ex: formatting a Date as "dd mmm yyyy": 12/25/06 → 25 Dec 2006
dynamic data structure
- data structures that can change in size during program execution - ex: linked-list, tree, history list in a browser
archive
- data that represents a record of data held and processed at a specific time, which is held off-line for future research or for legal reasons - examples: usually compressed, e.g. .zip or .tar, containing multiple files
client
- desk: computer or terminal used to access a computer-based system - ex: a secretary's work-station in a LAN, a PC surfing the Web
digital data
- discrete data - ex: ages = 10, 11 , 12, 13, NOT 10½ or 11.997 years; volume levels set to 0, 1, 2, 3, ...99, using switches rather than a rotating knob
attribute
- element of data contained in an object; as specified within the object's class - examples: window.width() , font.size()
FIFO
- first-in-first-out - ex: the lunch-line in the cafeteria (when the students obey the rules) - NOT an elevator, which is LIFO (last in first out)
browser
- generally used to give interactive access to information on the World Wide Web, retrieving web pages and displaying in a multi-media format - ex: Internet Explorer, Firefox, Netscape, Opera
encryption
- in computer security, the process of transforming data into an unintelligible form in such a way that the original data cannot be easily obtained except by using a decryption process - ex: PGP (pretty good privacy) is an encryption utility; it is a Public Key system, meaning the decryption key can be given out publicly, but the separate encryption key is a secret; then a properly encrypted message can only be sent by the owner of the private key - so the receiver can be certain of the identity of the sender; this provides a "digital signature"
floating point
- in floating point arithmetic, the position of the decimal point does not depend on the relative position of the digits in the numbers (as in fixed point arithmetic), since the two parts of the floating point number determine the absolute value of the number - ex: scientific notation; Avagadro's number = 6.02 X 10^23, a million = 1.0 X 10^6, nano = 1 X 10^-9
data security
- method of ensuring that data is correct, safe and cannot be read or changed by those who have no right to access it - ex: encryption, firewall, passwords
data protection
- method of ensuring that personal data is correct and is not misused either by those holding it or others who have no right to access it - ex: encryption, firewall, passwords, physical access protection (locked doors)
accessor methods
- methods that do not alter the state or attributes of an object; their purpose is to return information - examples: getText(), getSize(), etc.
data packet
- part of a transmitted message that is sent separately - apart from containing a portion of the message it will have other data such as check digits, destination address and so on - ex: In the Internet, big data files or messages are chopped up into small packets; the packets travel through the Internet and are re-assembled at the receiving end, without needing to arrive in the same order; each packet includes a header with the IP address of the destination, IP address of the sender, and error checking code
cache
- part of the main store that is between main memory and the processor - holds a copy of data and instructions that are likely to be used next by the processor and is hence faster than main memory - ex: Level I = inside CPU, Level II = on motherboard between CPU and RAM
address bus
- pathway from memory to processing unit that carries the address in memory to and from which data is transferred - examples: 32-bit address bus can address 2^32 = 4 GigaBytes of memory
fixed-length records
- records whose size is determined in advance. All such records in a file have the same length - ex: name as a String of 30 chars + Age as 32 bit integer = 34 bytes
CASE
- see the definition for "computer-assisted software engineering"
block
- smallest unit of data that can be transferred between memory and backing store in one operation - ex: cluster for a disk drive, typically 4 KiloBytes or 16 KiloBytes
ADSL (Asymmetrical Digital Subscriber Line)
- technology that increases the data rate over existing telephone lines accommodating voice and digital data transfer - a special modem is needed for access - examples: "Broadband": 1 - 16 MegaBits per second bandwidth
computer-assisted software engineering
- the automation of well-defined methodologies that are used in the development and maintenance of products - these methodologies apply to nearly every process or activity of a product development cycle, for example: project planning, product designing, coding and testing - ex: Visual designer like NetBeans, UML designer, debuggers, run-time efficiency profiler
base
- the basis of a notation or number system, defining a number representational system by positional representation - in a decimal system the base is 10, in a hexadecimal system the base is 16, and in a binary system the base is 2 - ex: Binary = BASE 2, Hexadecimal = BASE 16, Decimal = BASE 10
encapsulation
- the combination of data and the operations that act on the data to form a single program unit called an "object" - ex: Java classes contain both variables and methods in a single package, and can protect the variables from incorrect changes by declaring them private
data integrity
- the correctness of data after processing, storage or transmission - ex: use parity checks, checksums, CRC values
formal parameter
- the local name of a parameter inside a method, e.g. number in method below - ex: double root = cubeRoot( 125 ) ; public double cubeRoot(double number) { return Math.pow(number,1/3); }
computer architecture
- the logical structure and functional characteristics of a computer, including the interrelationships among its hardware and software components - ex: Wintel, Mac, Linux, Pocket PC - includes the chips/motherboard and the OS
and
- the output of "and" is True if all statements are True, False if any statement is False
data bus
- the pathway between the memory or peripheral and processing unit that carries data for processing or data that has been processed. See also definitions for "bus" and "address bus" - ex: usually the same as the Word-Size in the machine; but a 32-bit bus can be used twice to transfer a 64-bit word; bandwidth = bus width X bus speed, so a 500 Megahertz bus with 64 bit width can transfer 500 million X 8 Bytes = 4 Gigabytes per sec
bus
- the pathway used for sending signals between internal components of a computer - components can share the same bus but cannot transmit simultaneously - ex: CPU transmits an address to RAM across the 32 bit ADDRESS bus, RAM transmits data back across the 64-bit DATA bus
fixed points
- the performing of arithmetical calculations without regard to the position of the radix point - the relative position of the point has to be controlled during calculations - ex: money always has 2 decimal points, so 5.00 EU or 99.95 EU
ASCII: American Standard Code for Information Interchange
- the primary encoding character set used in computers for textual data transfer between applications - the set uses eight bits for each character code, one of these bits being a check bit to verify the seven bits needed to represent one character - ASCII supports most European alphabets - Unicode supports most known alphabets and is increasingly used in data transfer - examples: asc('A') --> 65, asc('9') --> 57, 0..127 = standard ASCII, 128..255 = extended ASCII
analog data
- the representation and measurement of the performance or behaviour of a system by continuously variable physical entities such as currents, voltages and so on - examples: sound waves, temperature, light waves (colors)
behaviour
- the way in which an object reacts to the methods applied - Usually determined by the METHODS in the object
enqueue
- to add an item to the rear of a queue - ex: when another patient enters the waiting room in a doctor's office, or you join the end of the queue in the lunch line
dequeue
- to remove an item from the front of a queue - see also the definition for "enqueue" - ex: in the doctor's waiting room, when they call the next patient; in a network, when the server delivers the next print-job to the printer
double buffering
- two areas of memory set aside for data transfer between the processor and peripherals - as one is emptied, the other is filled up in order to speed up transfer - ex: many video games use double buffering, drawing an entire picture and then quickly swapping the finished picture to the visible screen; then it draws in the second buffer before swapping it to the screen
cable
- wire or glass fibre used to connect computers over a network - copper (coaxial and twisted pair) and glass fibre (fibre optic cable) are the most common - ex: twisted pair for Starology, coaxial for a Busology, fibre-optic for WANs
