Barrons Publishing Dictionary of Computer and Internet Terms 10th

hard copy

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hard copy a printout on paper of computer output. Contrast SOFT COPY, which is a copy that is only viewable on the screen.

hard disk a data storage medium using rigid aluminum disks coated with iron oxide. The read-write head travels across the disk on a thin cushion of air without ever actually touching the disk.

Hard disks have much greater storage capacity than diskettes. In the early 1980s, 10 megabytes was a common size for hard disks. Today’s disks are measured in hundreds of gigabytes.

See also DISK; DISKETTE; HARD DISK MANAGEMENT. On the interface between the hard disk and the computer, see ESATA; ESDI; IDE; PATA; SATA;

SCSI.

hard disk management a task faced by all computer users. Modern hard disks are so large that it is easy to lose track of what you have stored on them. Here are some tips:

1.Be systematic. Choose a place to put files whenever there isn’t a good reason to put them elsewhere. In Windows, the Documents folder serves this purpose.

2.Use meaningful filenames. For example, a paper about African violets should be named AfricanViolets rather than av9247 or MyPaper. Add “-old,” “-previous,” or the like when you need to

keep more than one version of the same file.

3.Group files by project, not by software. For example, if you are writing a magazine article that consists of a word processing document and three pictures, create a folder for the project and put all four files in it.

4.Make backups. Your disk drive will fail one day, probably when you least expect it.

5.Learn how to search for misplaced files. In Windows, go to the Start Menu and choose Search or Find.

6.Defragment your hard disk every few weeks or months.

hard drive a HARD DISK.

hard drive enclosure a box in which a hard disk drive can be mounted instead of mounting it in the computer’s case.

hard edge in an image, an edge that is smooth and sharp, with no blending or blurring of the boundary. See Figure 127. Contrast SOFT EDGE.

FIGURE 127. Hard edge, left; Soft edge on right

VON NEUMANN ARCHI-

227 Hayes compatibility

hard error a persistent, reproducible error (defect) on a data storage device. Contrast SOFT ERROR.

hard hyphen see REQUIRED HYPHEN.

hard page a forced page break; a place where the word processor must begin a new page whether or not the previous page was full. In many PC word processors, the way to type a hard page is to hold down the Ctrl key while pressing Enter.

hardware the physical elements of a computer system; the computer equipment as opposed to the programs or information stored in the machine. Contrast SOFTWARE.

hardware interrupt a CPU interrupt triggered by a hardware event, such as pressing a key. See INTERRUPT.

hardware key a device that attaches to a computer to prove that it is licensed to run a particular piece of software; a dongle. See DONGLE.

Harvard architecture a type of computer design in which the program and the data are stored in separate memories. Contrast

TECTURE. See COMPUTER ARCHITECTURE.

hash function a function that converts a string of characters to a number or a shorter string. During data transmission, the value of an agreed-upon hash function can be transmitted along with the data so it can be verified if the data has been transmitted correctly. For example, see CHECKSUM. A one-way hash function is a hash function that is also a one-way function.

See ENCRYPTION; ONE-WAY FUNCTION.

hashing a storage mechanism where data items are stored at locations that are determined by a mathematical function of the data. For example, suppose you need to store a set of numbers in memory locations whose addresses run from 1 to 100. One example of a hashing function is to divide each number by 100 and use the remainder as the storage address. For example, the number 538 would be stored at memory location 38, and 1124 would be stored at location 24.

The use of hashing makes it possible to store and retrieve the data items quickly, since it is not necessary to search through the list in order to find the item. However, there is one complication: A hashing function will sometimes assign more than one data item to the same address. For example, using the rule given, the number 638 would also be stored in location 38. To avoid that problem, a hashing system needs to be able to resolve collisions by storing the new data item in a separate place.

hat

1.the character ˆ (circumflex).

2.See BLACK HAT; RED HAT; WHITE HAT.

Hayes compatibility the ability of a telephone line modem to respond to the same set of autodialing commands as the Hayes Smartmodem (made

HD DVD

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by Hayes Microcomputer Products, Inc., Norcross, Georgia). Almost all modems nowadays are Hayes compatible.

Modems need not be Hayes compatible in order to communicate with each other. Hayes compatibility refers only to the commands used by the computer to control the modem. They are often called the AT COMMAND SET and begin with the letters AT. For example,

ATDT706-555-2345

tells the modem to dial 706-555-2345. See also MODEM; RS-232.

HD DVD (high-density DVD) a high-density optical disc similar to, but not compatible with, BLU-RAY DISC, formerly marketed by Toshiba but discontinued in 2008.

HDD hard disk drive.

HDMI (High-Definition Multimedia Interface) a standard interface and cable connector for carrying digitized audio and video. The connector is small and flat, like a USB connector, but is even smaller and contains 19 pins. Compare DVI (definition 1). For more information see www.hdmi.org.

HDSL (High-bit-rate Digital Subscriber Line) a type of high-speed network connection provided through ordinary telephone lines. Unlike ordinary DSL (ADSL), HDSL is symmetric (i.e., the upload and download speeds are both 1.5 Mbps), but ordinary telephone service is not included. See DSL and cross-references there.

HDTV high-definition television; television with a resolution of 1280 × 720 pixels or more and, normally, a widescreen format with an aspect ratio of 16:9. Although analog HDTV was attempted in the 1990s, HDTV is now broadcast digitally because digital data compression is essential to its success. Contrast SDTV.

head

1.the part of a disk drive that reads and writes information magnetically. A double-sided disk drive or multilayered hard disk has a head for each side of each layer. (See DISK.)

2.the top of a page or printed piece (such as a newsletter).

3.short for headline.

4.tag used in HTML to indicate the beginning of the heading of a web page, which includes material such as the title. Contrast BODY. For an example, see HTML.

headless term describing a computer that lacks a keyboard, screen, and a mouse.

headset speakers (or rather earphones) and (usually) a microphone worn on a person’s head.

heap a block of memory that belongs to a program but has not yet been

229

hertz

given a specific use. For example, when a C# program creates character strings, it typically places them in space obtained from its heap.

heat sink a device to carry heat away from an electronic component. The heat sink for a CPU is typically a chunk of metal with fins or fingers, accompanied by a cooling fan. A vital part of the system is a thin layer of thermally conductive paste that conducts heat from the CPU to the metal heat sink. If this paste deteriorates or is missing, the CPU will run hot no matter how good the heat sink. See also OVERCLOCKING.

hecta- metric prefix meaning ×100 (102). Hecta- is derived from the Greek word for “hundred.” See METRIC PREFIXES.

Heisenbug (humorous) a bug (error) in a computer program that goes away or radically changes its behavior when attempts are made to investigate it.

This is a common phenomenon. If the bug involves an UNINITIALIZED VARIABLE, the contents of the variable will be affected by other programs that have run recently. Thus, any attempt to investigate the bug will change its behavior. (From Heisenberg’s uncertainty principle in physics, which states that it is impossible to determine the exact position and the exact momentum of an object at the same time; any attempt to measure one will change the other.)

See also BUG.

Hejlsberg, Anders see C#; DELPHI.

hello-world program a program that simply writes “Hello, world” on the most convenient output device, and terminates. Hello-world programs are the traditional way to verify that programming languages and output devices are working, at least to a minimal degree.

help information provided by a computer program to assist the user. Many computer programs contain an on-screen help facility that a user can turn to when questions arise. For example, if you have forgotten how a particular command works, you can consult a help facility (if one is available) to refresh your memory.

In Windows programs, one of the menu choices is usually Help. Windows has an elaborate help system accessible from the Start button.

See also CONTEXT-SENSITIVE HELP; DOCUMENTATION.

help desk, helpdesk a place where people who use computers can go for assistance; it may be a single desk or a whole department of a large organization.

Helvetica a popular sans-serif typeface designed around 1957 by M. Miedinger.

hertz the number of times something is repeated per second; a unit of frequency, abbreviated Hz and named for Heinrich Hertz, discoverer of radio waves. See also CLOCK; GIGAHERTZ; MEGAHERTZ.

heuristic

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FIGURE 128. Helvetica (normal weight)

heuristic a method of solving problems that involves intelligent trial and error. By contrast, an algorithmic solution method is a clearly specified procedure that is guaranteed to give the correct answer. (See ALGORITHM.) For example, there is no known algorithm that tells how to play a perfect game of chess, so computer chess-playing programs must use a heuristic method of solution, using methods that are likely but not certain to give good results in any particular case.

Hewlett-Packard (HP) a leading manufacturer of computers and printers. Hewlett-Packard is headquartered in Palo Alto, California, and can be reached on the web at www.hp.com. The electronic test equipment division of HP is now a separate company known as Agilent.

TABLE 7

HEXADECIMAL EQUIVALENTS OF BINARY NUMBERS

Binary	Hex	Binary	Hex
0000	0	1000	8
0001	1	1001	9
0010	2	1010	A
0011	3	1011	B
0100	4	1100	C
0101	5	1101	D
0110	6	1110	E
0111	7	1111	F

hexadecimal number a number written in base 16. Hexadecimal numbers use 16 possible digits, written 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A (= 10), B (=11), C (=12), D (= 13), E (= 14), and F (= 15). For an example, the number A4C2 in hexadecimal means:

10 × 163 + 4 × 162 + 12 × 161 +2 × 160 = 42,178

Hexadecimal numbers provide a good shorthand way of representing binary numbers, since binary numbers can be converted to hexadecimal

231	hexadecimal number

numbers by looking at only four digits at a time. For example, binary 1111 equals hexadecimal F, binary 0100 equals hexadecimal 4, and binary 11110100 equals hexadecimal F4:

11110100 F 4

When converting a binary number to hexadecimal by this method, start by adding zeros at the left in order to make the number of digits a multiple of 4.

Table 7 shows the hexadecimal equivalents of the four-digit binary numbers, and Table 8 shows the decimal equivalents of the hexadecimal numbers from 00 to FF.

TABLE 8

HEXADECIMAL NUMBERS AND DECIMAL EQUIVALENTS (Part 1)

00	=	0	20	=	32	40	=	64	60	=	96
01	=	1	21	=	33	41	=	65	61	=	97
02	=	2	22	=	34	42	=	66	62	=	98
03	=	3	23	=	35	43	=	67	63	=	99
04	=	4	24	=	36	44	=	68	64	=	100
05	=	5	25	=	37	45	=	69	65	=	101
06	=	6	26	=	38	46	=	70	66	=	102
07	=	7	27	=	39	47	=	71	67	=	103
08	=	8	28	=	40	48	=	72	68	=	104
09	=	9	29	=	41	49	=	73	69	=	105
0A	=	10	2A	=	42	4A	=	74	6A	=	106
0B	=	11	2B	=	43	4B	=	75	6B	=	107
0C	=	12	2C	=	44	4C	=	76	6C	=	108
0D	=	13	2D	=	45	4D	=	77	6D	=	109
0E	=	14	2E	=	46	4E	=	78	6E	=	110
0F	=	15	2F	=	47	4F	=	79	6F	=	111
10	=	16	30	=	48	50	=	80	70	=	112
11	=	17	31	=	49	51	=	81	71	=	113
12	=	18	32	=	50	52	=	82	72	=	114
13	=	19	33	=	51	53	=	83	73	=	115
14	=	20	34	=	52	54	=	84	74	=	116
15	=	21	35	=	53	55	=	85	75	=	117
16	=	22	36	=	54	56	=	86	76	=	118
17	=	23	37	=	55	57	=	87	77	=	119
18	=	24	38	=	56	58	=	88	78	=	120
19	=	25	39	=	57	59	=	89	79	=	121
1A	=	26	3A	=	58	5A	=	90	7A	=	122
1B	=	27	3B	=	59	5B	=	91	7B	=	123
1C	=	28	3C	=	60	5C	=	92	7C	=	124
1D	=	29	3D	=	61	5D	=	93	7D	=	125
1E	=	30	3E	=	62	5E	=	94	7E	=	126
1F	=	31	3F	=	63	5F	=	95	7F	=	127

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TABLE 8

HEXADECIMAL NUMBERS AND DECIMAL EQUIVALENTS (Part 2)

80	=	128	A0	=	160	C0	=	192	E0	=	224
81	=	129	A1	=	161	C1	=	193	E1	=	225
82	=	130	A2	=	162	C2	=	194	E2	=	226
83	=	131	A3	=	163	C3	=	195	E3	=	227
84	=	132	A4	=	164	C4	=	196	E4	=	228
85	=	133	A5	=	165	C5	=	197	E5	=	229
86	=	134	A6	=	166	C6	=	198	E6	=	230
87	=	135	A7	=	167	C7	=	199	E7	=	231
88	=	136	A8	=	168	C8	=	200	E8	=	232
89	=	137	A9	=	169	C9	=	201	E9	=	233
8A	=	138	AA	=	170	CA	=	202	EA	=	234
8B	=	139	AB	=	171	CB	=	203	EB	=	235
8C	=	140	AC	=	172	CC	=	204	EC	=	236
8D	=	141	AD	=	173	CD	=	205	ED	=	237
8E	=	142	AE	=	174	CE	=	206	EE	=	238
8F	=	143	AF	=	175	CF	=	207	EF	=	239
90	=	144	B0	=	176	D0	=	208	F0	=	240
91	=	145	B1	=	177	D1	=	209	F1	=	241
92	=	146	B2	=	178	D2	=	210	F2	=	242
93	=	147	B3	=	179	D3	=	211	F3	=	243
94	=	148	B4	=	180	D4	=	212	F4	=	244
95	=	149	B5	=	181	D5	=	213	F5	=	245
96	=	150	B6	=	182	D6	=	214	F6	=	246
97	=	151	B7	=	183	D7	=	215	F7	=	247
98	=	152	B8	=	184	D8	=	216	F8	=	248
99	=	153	B9	=	185	D9	=	217	F9	=	249
9A	=	154	BA	=	186	DA	=	218	FA	=	250
9B	=	155	BB	=	187	DB	=	219	FB	=	251
9C	=	156	BC	=	188	DC	=	220	FC	=	252
9D	=	157	BD	=	189	DD	=	221	FD	=	253
9E	=	158	BE	=	190	DE	=	222	FE	=	254
9F	=	159	BF	=	191	DF	=	223	FF	=	255

HFS see HIERARCHICAL FILE SYSTEM (definition 2).

hibernate to suspend the operation of a computer by copying the entire contents of memory to a disk file, so that the computer can be powered off, then turned on again to resume where it left off, without rebooting. While hibernating, a computer consumes no electric power. Contrast SUSPEND.

hibernation file the data file on which the contents of memory are written when a computer hibernates. See HIBERNATE.

hidden file a file whose presence is normally concealed from the user to keep it from being deleted or moved. Hidden files contain information used by the operating system. Under Windows, hidden files in a folder can be viewed by making the appropriate choice under “Tools, Folder Options” on the menu bar.

233	High Sierra format

hierarchical arranged in such a way that some items are above or below others in a tree-like structure. Examples of hierarchies include the organizational chart of a corporation, the arrangement of directories on a disk, and the arrangement of windows on a screen (because some of the windows are within others).

The root of the hierarchy is the main item that is above all of the others, such as the CEO of a corporation, the root directory of a disk, or the window that comprises the whole screen.

Many menu systems are arranged hierarchically, as menus within menus. For other examples of hierarchical data structures, see DIRECTORY; OUTLINE; TREE.

FIGURE 129. Hierarchical file system

hierarchical file system

1.a file system that allows subdirectories or folders to belong to a higher-level subdirectory or folder (Figure 129). See DIRECTORY.

2.(capitalized, Hierarchical File System, abbreviated HFS) the file system of the Macintosh. Besides disk drives, HFS is sometimes used on CDs, rendering them unreadable on computers other than the Macintosh.

Compare JOLIET FILE SYSTEM; ROCK RIDGE.

hierarchical menu a menu with other menus under it; a CASCADING MENU. For an example, see START BUTTON.

high-level language a computer programming language designed to allow people to write programs without having to understand the inner workings of the computer. BASIC, C, Pascal, and Java are examples of highlevel languages. By contrast, a machine language is at the lowest level, since machine language programming requires detailed knowledge of the computer’s inner workings. An assembly language is at a slightly higher level than a machine language, since it uses a notation more convenient for the programmer.

High Sierra format a standard format for recording files and directories on CD-ROMs, now superseded by ISO 9660. The two formats are closely

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compatible, but some of the earliest CD-ROM software could read only High Sierra format disks.

highlight

1.to make a menu item prominent (either lighter or darker than the others) to show that it is selected. In most graphical user interfaces, you can choose the highlighted item by pressing Enter.

2.the lightest part of an image. In artwork, highlights show texture, shape, and the direction of the source of light.

HighMAT (High-performance Media Access Technology) a set of standards co-developed by Microsoft and Matsushita (Panasonic) for CDs and DVDs that are created on personal computers but played back on consumer electronic devices such as CD players and DVD-equipped television sets. HighMAT provides a standard way for the user to organize the files and select them for playback.

hinting additional information encoded into a digital font to help the computer software correctly display and print the letters at different sizes and resolutions.

HIPAA compliant meeting the standards set by the Health Insurance Portability and Accountability Act of 1996 for electronic data interchange. See aspe.hhs.gov/admnsimp.

hiragana see KANA.

histogram a bar graph in which the bars represent how many times something occurs (Figure 130). Histograms are often used in paint programs and scanner software to allow direct manipulation of the image characteristics. Each bar represents the total number of pixels of a particular shade of gray. By sliding the endpoints closer together, you decrease the image contrast; sliding the endpoints apart increases contrast. See also

BRIGHTNESS; CONTRAST.

FIGURE 130. Histogram

history folder a folder that contains a list of the locations you have visited on the Internet.

hit

1. something found by a searching. For instance, if you search the Web for instances of the word “aardvark” and find 250 of them, you’ve found 250 hits.

FOAF; PYRAMID SCHEME.

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hole

2. on the World Wide Web, an instance of someone elsewhere calling up the web page and viewing it. The popularity of a web site is measured in hits per day.

hive a major section of the Windows REGISTRY that is automatically backed up on an external file. Examples of hives include HKEY_CURRENT_USER,

HKEY_CURRENT_CONFIG, and HKEY_LOCAL_MACHINE\System. Not all of the top-level branches of the registry are hives.

hoax a piece of misinformation circulated as a deliberate prank; common on the Internet. (Compare MEME virus.) Hoaxes usually arrive in e-mail messages that say “mail this to all your friends”—that is, the hoaxer does not want you to post the message in a public forum where knowledgeable people might debunk it. Some common Internet hoaxes are the following:

1.“A dying child (or maybe a charity) wants a gigantic number of postcards or a gigantic amount of e-mail.” Nobody wants a gigantic amount of e-mail; e-mail costs money to receive.

One young cancer victim, Craig Shergold, did appeal for postcards in 1989; his story is told in the Guinness Book of World Records, and his family is begging for the flood of postcards to stop. Unfortunately, his story is still circulating, often with altered names and addresses.

2.“Some branch of government, such as the FCC, is about to do something outlandish.”

Sometimes these warnings come from well-meaning activists; more often they are pranks. In the 1970s a disgruntled license applicant started a rumor that the FCC was about to ban all religious broadcasting; the story is still circulating and the FCC can’t afford to answer the flood of correspondence that it has generated. Newer hoaxes include a “modem tax” or bans on various uses of the Internet.

3.“If you get e-mail titled ‘Good times’ (or ‘Happy birthday’ or ‘Deeyenda’ or something else), it will erase your hard disk (or do other great harm).”

Any file attached to e-mail could easily contain a virus or destructive program; do not open such files unless you are sure of their origin. However, the viruses described in these particular hoaxes apparently do not exist.

Any piece of e-mail that is designed to spur you to immediate action is likely to be a hoax; before passing it on, you should check it out with your system administrator, your local computer security team, or another knowledgeable person. Better yet, do a web search to see what you can find out about it. The web site www.snopes.com specializes in debunking hoaxes and revealing the real facts. See also

Compare URBAN LEGEND.

hole a place where an electron is missing from the crystal structure of a P- type semiconductor. A hole acts as a moving positive charge. See SEMICONDUCTOR.