Barrons Publishing Dictionary of Computer and Internet Terms 10th
.pdf
BSD |
66 |
FIGURE 41. Browser displaying a web page
BSD a version of UNIX that was developed at the University of California at Berkeley (UCB). (See UNIX.) BSD UNIX introduced the vi full-screen editor and a number of other enhancements. SunOS (Solaris) and System V are combinations of BSD UNIX with the original AT&T UNIX.
BSOD see BLUE SCREEN OF DEATH.
BTW online abbreviation for “by the way.”
bubble sort an algorithm for arranging items in order, as follows: First, examine the first two items in the list. If they are in order, leave them alone; if not, interchange them. Do the same with the second and third items, then with the third and fourth items, until you have reached the last two. At this point you are guaranteed that the item that should come last in the list has indeed “bubbled” up to that position. Now repeat the whole process for the first n – 1 items in the list, then for n – 2, and so on.
Bubble sort is not a particularly fast sorting algorithm on conventional computers, but it works well on parallel computers that can work on different parts of the list simultaneously.
Figure 42 shows a Java program that performs a bubble sort. For clarity, this version of the algorithm does not use element 0 of the array.
buddy list a set of online friends, with contact information. Most instant messaging programs have buddy lists, which not only keep track of your chatting buddies but show whether or not they are presently logged in.
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buffer |
class |
bubblesort |
{ |
|
/* This Java program performs a bubble sort */ /* Array to be sorted and number of items in it.
Element a[0], which contains 0 here, is ignored. */ static int a[] = {0,29,18,7,56,64,33,128,70,78,81,12,5}; static int n=12;
public static void main(String args[])
{
/* Perform the bubble sort */
for (int i=1; i<=n; i++)
{
for (int j=1; j<=(n-i); j++)
{
if (a[j]>a[j+1])
{
int t=a[j]; a[j]=a[j+1]; a[j+1]=t;
}
}
}
/* Display the results */
for (int i=1; i<=n; i++)
{
System.out.println(a[i]);
}
}
}
FIGURE 42. Bubble sort
buffer
1.areas in memory that hold data being sent to a printer or received from a serial port. The idea here is that the printer is much slower than the computer, and it is helpful if the computer can prepare the data all at once, and then dole it out slowly from the buffer as needed. Similarly, a serial port needs a buffer because data may come in when the computer is not ready to receive it.
2.an area in memory that holds a file that is being edited. Some editors allow you to edit more than one file at once, and each file occupies its own buffer.
3.an area in memory that holds data being sent to, or received from, a disk. Some operating systems allow you to adjust the size or number of disk buffers to fit the speed of your disk drive. See also UNDERRUN.
4.an area in memory that holds signals from keys that have been pressed but have not yet been accepted by the computer.
5.an electronic device whose output is the same as its input (e.g., an amplifier for driving long cables).
bug |
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bug an error in a computer program. The term is somewhat misleading because it suggests that errors have a life of their own, which they do not. Bugs fall into at least three classes: syntax errors, where the rules of the programming language were not followed; semantic errors, where the programmer misunderstood the meaning of something in the programming language; and logic errors, where the programmer specified some detail of the computation incorrectly. Nowadays there is beginning to be a serious problem with a fourth class, which can be called infrastructure errors, where the programmer fell victim to something wrong with the operating system or a programming tool.
build
1.(verb) to put together a piece of software from its components by compiling, linking, and doing whatever else is necessary to make a working, deliverable version. See COMPILER; LINKER.
2.(noun) the result of building a piece of software on a particular occasion. Some software developers keep track of build numbers, which change much more rapidly than version numbers.
built fraction a fraction that is composed by setting the numerator and denominator as regular numerals separated by a forward slash (1/2, 1/4).
Contrast CASE FRACTION; PIECE FRACTION.
FIGURE 43. Built fraction (center) vs. case and piece fractions
bullet a character such as • used to mark items in a list.
bulletin board a message board; an online service where people can post messages. See MESSAGE BOARD.
bundled software software that is sold in combination with hardware. For example, software for processing speech and music is often bundled with sound cards.
burn (slang) to record information on a CD or DVD disc or an EPROM.
bus the main communication avenue in a computer. For a diagram, see
COMPUTER ARCHITECTURE.
The bus consists of a set of parallel wires or lines to which the CPU, the memory, and all input-output devices are connected. The bus contains one line for each bit needed to give the address of a device or a location in memory, plus one line for each bit of data to be transmitted
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button bar |
in a single step, and additional lines that indicate what operation is being performed.
Most personal computers today use a 32-bit bus, but on PC-compati- bles, the bus can also work in 8-bit and 16-bit mode.
Here is how an 8-bit bus works: If the CPU wants to place the value 00011001 into memory location 10100000, it places 00011001 on the data lines, places 10100000 on the address lines, and places 1 (rather than the usual 0) on the “write memory” line. The memory unit is responsible for recognizing the “write memory” request, decoding the address, and storing the data in the right location.
The bus can transmit data in either direction between any two components of the system. If the computer did not have a bus, it would need separate wires for all possible connections between components. See also EISA; ISA; PCI; PCMCIA; SERIAL BUS.
button a small circle or rectangular bar within a windowed DIALOG BOX that represents a choice to be made. One of the buttons in a group is normally highlighted, either by having a black circle inside of it or having a heavy black border. This represents the DEFAULT choice. You can choose any one of the buttons by clicking on it with the mouse.
There are two kinds of buttons: OPTION BUTTONS (sometimes called radio buttons) and command buttons. Option buttons represent mutually exclusive settings; that is, you can choose only one. They are usually small and round but are sometimes diamond-shaped. If you change your mind and click on another option button, your original choice will be grayed (dimmed). See CLICK; DIALOG BOX; DIMMED; HIGHLIGHT.
Command buttons cause something to happen immediately when you click on them. They are usually rectangular and larger than option buttons. The most familiar examples are the OK and Cancel buttons that are in almost every dialog box. If the command button brings up another dialog box, you will see an ELLIPSIS (. . . ) after its label.
FIGURE 44. Buttons: option buttons (left) and command buttons (right)
button bar a row of small icons usually arranged across the top of the workspace on the screen. Each icon represents a commonly used command; many programs allow you to customize your button bar to suit your taste.
bwahahahaha |
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FIGURE 45. Button bars
bwahahahaha typewritten representation of an evil laugh.
Byron, Augusta Ada see ADA.
byte the amount of memory space needed to store one character, which is normally 8 bits. A computer with 8-bit bytes can distinguish 28 = 256 different characters. See ASCII for the code that most computers use to represent characters.
The size of a computer’s memory is measured in kilobytes (= 210 = 1024 bytes) or megabytes (= 220 =1,048,576 bytes).
bytecode the concise instructions produced by compiling a Java program. This bytecode is the same for all platforms; it is executed by a Java virtual machine. See JAVA; JVM. See also .NET FRAMEWORK.
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C |
C
C a programming language developed at Bell Laboratories in the 1970s, based on the two earlier languages B (1970) and BCPL (1967). A C compiler is provided as a part of the UNIX operating system (see UNIX), and C was used to write most of UNIX itself. In addition, C is popular as an alternative to assembly language for writing highly efficient microcomputer programs. There is a widespread (and often mistaken) belief that programs written in C are more efficient than programs written in any other language.
C is a general-purpose language like Pascal and ALGOL, but, unlike other general-purpose languages, it gives the programmer complete access to the machine’s internal (bit-by-bit) representation of all types of data. This makes it convenient to perform tasks that would ordinarily require assembly language, and to perform computations in the most efficient way of which the machine is capable.
/* CHKSUM.C */
/* Sample program in C —M. Covington 1991 */ /* Based on a program by McLowery Elrod */
/* Reads a character string from the keyboard */ /* and computes a checksum for it. */
#include <stdio.h>
#define N 256
main()
{
int i, n; char str[N];
puts(”Type a character string:”); gets(str);
printf(”The checksum is %d\n”,chksum(str));
}
chksum(s,n) char* s; int n;
{
unsigned c; c = 0;
while (n— >0) c = c + *s++; c = c % 256;
return(c);
}
FIGURE 46. C program
C++ |
72 |
In C, things that are easy for the CPU are easy for the programmer, and vice versa. For example, character string handling is somewhat clumsy because the CPU can only do it through explicit procedure calls. But integer arithmetic is very simple to program because it is simple for the CPU to execute. Most programmers who use C find themselves writing efficient programs simply because the language pushes them to do so.
Figure 46 shows a program written in C. This language encourages structured programming; the three loop constructs are while, do, and for. The comment delimiters are /* */. A semicolon comes at the end of every statement (unlike Pascal, where semicolons only come between statements).
C allows operations to be mixed with expressions in a unique way. The expression i++ means “retrieve the value of i and then add 1 to it.” So if i equals 2, the statement j = (i++)*3 will make j equal 6 (i.e., 2 × 3) and will make i equal 3 (by adding 1 to it after its value is retrieved; but notice that its old value was used in the multiplication).
Another noteworthy feature of C is the #define statement. The sample program contains the line
#define N 256
which tells the compiler that wherever N occurs as a symbol in the program, it should be understood as the number 256. See also C++.
C++ an object-oriented programming language developed by Bjarne Stroustrup at Bell Laboratories in the mid-1980s as a successor to C. In C and C++, the expression C++ means “add 1 to C.”
Figure 47 shows a program in C++. Comments are introduced by // and object types are declared as class. The part of an object that is accessible to the outside world is declared as public. For an explanation of what this program does, see OBJECT-ORIENTED PROGRAMMING, where the equivalent Java code is explained.
In C++, input-output devices are known as streams. The statement
cout << ”The answer is ” << i;
sends “The answer is” and the value of i to the standard output stream. This provides a convenient way to print any kind of data for which a print method is defined.
C++ lets the programmer overload operators (give additional meanings to them). For example, + normally stands for integer and floatingpoint addition. In C++, you can define it to do other things to other kinds of data, such as summing matrices or concatenating strings.
C++ is the basis of the Java and C# programming languages.
See JAVA; C#.
73 |
CA |
//SAMPLE.CPP
//Sample C++ program —M. Covington 1991
//Uses Turbo C++ graphics procedures
#include <graphics.h>
class pnttype { public:
int x, y;
void draw() { putpixel(x,y,WHITE); }
};
class cirtype: public pnttype { public:
int radius;
void draw() { circle(x,y,radius); }
};
main()
{
int driver, mode; driver = VGA; mode = VGAHI;
initgraph(&driver,&mode,”d:\tp\bgi”);
pnttype a,b; cirtype c;
a.x = 100; a.y = 150; a.draw();
c.x = 200; c.y = 250;
c.radius = 40; c.draw();
closegraph;
}
FIGURE 47. C++ program
C# (pronounced “C sharp”) a programming language developed by Anders Hejlsberg (the developer of Turbo Pascal and Delphi) for Windows programming under Microsoft’s .NET Framework.
C# is similar in appearance and intent to Java, but it is more tightly tied to the object-oriented operating-system interface of the .NET Framework. In some ways it reflects the spirit of Pascal, with clean and simple design, but it is fully object-oriented. Memory allocation is automatic, and programmers do not normally manipulate pointers. Care has been taken to make common operations simple and concise, and the handling of windows is especially straightforward; programmers never have to declare handlers for events that they do not actually want to handle.
Figure 48 on page 74 shows a sample program in C#. Compare it to the sample Pascal program on page 356.
CA (certificate authority) an agency that issues digital certificates. See CERTIFICATE, DIGITAL; DIGITAL SIGNATURE.
cable modem |
74 |
using System; class primecheck
{
// Sample C# program to test whether a number is prime. static void Main(string[] args)
{
int n, i, max; bool cont; string s;
while (true)
{
Console.Write(”Type a number (0 to quit): ”); n = Convert.ToInt32(Console.ReadLine());
if (n==0) break;
s = ”prime”; cont = (n > 2); i = 1;
max = (int)Math.Sqrt(n); // largest divisor to try while (cont)
{
i++;
Console.WriteLine(”Trying divisor {0}”,i); if (n % i == 0) //if n divisible by i
{
s = ”not prime”; cont = false;
}
else
{
cont = (i < max);
}
}
Console.WriteLine(”{0} is {1} \n”,n,s);
}
}
}
FIGURE 48. C# program
cable modem a MODEM that provides computer communication over television cables (either coaxial or fiber-optic) rather than telephone lines.
cache
1. a place where data can be stored to avoid having to read the data from a slower device such as a disk. For instance, a disk cache stores copies of frequently used disk sectors in RAM so that they can be read without accessing the disk.
The 486 and Pentium microprocessors have an internal instruction cache for program instructions that are being read in from RAM; an external cache is also used, consisting of RAM chips that are faster than those used in the computer’s main memory. See also L1 CACHE; L2 CACHE.
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Cairo |
2. a set of files kept by a WEB BROWSER to avoid having to download the same material repeatedly. Most web browsers keep copies of all the web pages that you view, up to a certain limit, so that the same pages can be redisplayed quickly when you go back to them. If a web page has been changed recently, you may have to RELOAD it to see its current contents.
cacls (presumably: change access control lists) a powerful console-mode command in Windows 2000 and its successors for changing permissions and security attributes of files, analogous to CHMOD in UNIX. For example, the command
cacls myfile.txt /g ”Domain Users”:R
gives all members of the group “Domain Users” permission to read myfile.txt. For full documentation type:
cacls /?
The cacls command is used mainly in BAT files, since you can also change permissions by right-clicking on the file or folder and following the menus. See also CHMOD; PERMISSION.
CAD (Computer-Aided Design) the use of a computer for design work in fields such as engineering or architecture, with the computer’s graphics capabilities substituting for work that traditionally would have been done with pencil and paper. In order to do CAD, it is necessary to have a highresolution monitor and a software package designed for the purpose.
In order to draw a building, for example, it is necessary to enter the plans by using a graphical input device, such as a mouse or graphics tablet. There are several advantages to having the plans in the computer:
1.The computer can automatically calculate dimensions. In fact, the ability to calculate dimensions is the biggest difference between CAD programs and ordinary draw programs.
2.Changes can be made easily (e.g., adding a new wall).
3.Repetitive structures can be added easily.
4.The image can be enlarged to obtain a close-up view of a particular part, or it can be shrunk to make it possible to obtain an overall view. The image can be rotated to view it from many different perspectives. For example, the Boeing 777 airplane, first rolled out in 1994, was designed entirely on computers. Previous airplanes had been designed the traditional way with paper drawings, and then a full-scale mock-up had to be constructed to make sure that the parts would fit together in reality as they did on paper. CAD made this extra work unnecessary.
CAI (computer-aided instruction) teaching any kind of knowledge to people with the aid of a computer.
Cairo Microsoft’s code name for a version of Windows under development during the mid-1990s. As it turned out, no single version of Windows