ii}: the Editors ofi'he
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`A M E R I CAN H E RITAG EH Dictionaries
`
`AN A TO Z GUIDE
`
`TO HARDWARE,
`
`SOFTWARE,
`
`AND CYBERSPACE
`
`dictionary
`aggfcomputer
`Internet
`words
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`Facebook's Exhibit No. 1015
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`Snap's Exhibit No. 1015
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`memory
`
`2. The capacity of a computer, chips, and
`memory 1. See RAM.
`storage devices to preserve data and programs for retrieval. Memory
`is measured in bytes
`3. A system for preserving data and pro-
`grams for retrieval. Volatile memory, or RAM, stores information
`only until the power is turned off. Nonvolah‘le memory stores mem»
`
`ory even when the power is off. Nonvolatile memory includes ROM,
`PROM, EPROM, and EEPROM, as well as such external devices as
`
`disk drives and tape drives. See also expanded memory, extended
`memory, flash memory, main memory, and virtual memory.
`memory card A storage device that uses a variety of types of chip, in-
`cluding RAM, ROM, EEPROM, and flash memory. Since the data
`stored in a memory card remains intact even when the power is
`turned off and you can rewrite data without removing the card from
`the computer's circuit board, the memory card functions as a substi—
`tute for a hard disk. Memory cards are often used in handheld de-
`vices, such as PDAs and digital cameras.
`memory effect A property of NiCad batteries in which the amount of
`charging they accept at one time fixes the maximum amount of
`charging they can accept in subsequent recharges. NiCad batteries
`are used, for example, in laptop computers. The memory effect is re-
`lated to the recharging of a battery that is not 100% drained. If a
`battery is only 90% drained, it will only require 10% of the full
`power to recharge. Because of the memory effect, in the future that
`battery will only accept a maximum of 10% recharging.
`memory management unit See MMU.
`
`memory-resident Designating a program that remains permanently
`in a computer’s RAM. The CPU (central processing unit) must load a
`file or program into RAM before it can be processed. Other data or
`programs are copied or swapped from RAM onto disk to make room
`for the program that you are running, but a memory-resident pro-
`gram will not be moved from RAM. Central parts of the operating
`system are memory-resident, as are utilities or accessory programs
`such as calendars, calculators, and spell checkers. These memory—
`resident programs are activated when you press a simple key se-
`quence knowri as a hot key. Also called RAM-resident.
`
`menu An onscreen list of available options or commands. Usually the
`options are highlighted by a bar that you can move from one item
`to another. You can choose a menu item by keying in its code or by
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`merge
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`pull-clown menu
`cascading menu
`
`
`
`MENU On an Apple Macintosh computer
`
`pointing to the item with the mouse and clicking a mouse button.
`
`Choosing often leads to a submenu, called a cascading menu, or to
`a dialog box containing options that further refine the original
`menu selection. See illustration. See also menu bar, pull-down
`menu, tear-off menu.
`
`menu bar A horizontal bar that runs across the top of the screen or of
`a window and holds the names of available menu options. When
`
`you choose an option from the menu bar, another list of commands
`or options drops down below the bar. See also menu.
`
`menu—driven Of or relating to a type of user interface in which the
`user issues commands by making selections from on-screen menus.
`
`Menu-driven programs are easier to use than command-driven pro-
`grams, which require you to learn and type in commands, because
`in a menu—driven program, the command choices are all there in
`
`front of you.
`
`1. To combine two files into one so that the resulting file
`merge v.
`has the same structure as each of its components. If you merge two
`files, each containing an alphabetically arranged list of names,
`the resulting file will contain all of the names from the two files in
`
`alphabetical order. In contrast, if you were to append the same
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`publish and subscribe
`
`situations in which a sender and a recipient wish to communicate
`securely and in which speed is not important. In public key cryptog-
`raphy there is a public list of encryption keys each corresponding to
`one individual recipient. In order for a person to send an encrypted
`message, the sender must look up the intended recipient's public key
`and encrypt the message using that. Each recipient privately holds
`the key necessary for decryption; it is impossible, in practical terms,
`for anyone to guess the private decryption key from the public en~
`cryption key.
`
`Public key cryptography is different from traditional encryption,
`in which the encryption and decryption keys are fundamentally
`identical. Traditional encryption is less secure, since one has to
`
`communicate the key in some manner, but it is a faster system for
`decoding than public cryptography. See also ciphertext, encryp-
`tion, plaintext.
`
`publish and subscribe The capability for linking portions of docu-
`ments and establishing how updates to the data in one document
`affect the data in other documents. If a portion of a document is
`published, then a change made to this portion is automatically
`updated to subscriber versions contained in other documents. Publish
`
`and subscribe became available in Apple Computer’s System 7 oper-
`ating system, which was a major upgrade of the Macintosh System.
`puck An input device that resembles a mouse but has a clear plastic
`section that is marked with cross hairs. It is used on a digitizer to
`trace accurately a hard copy of a graphical image into a form that
`can be used by the computer. Pucks are often used in architectural
`and engineering applications.
`
`pull-down menu A pop-up window that appears directly beneath
`the item selected on a menu bar. Also called drop—down menu. See
`illustration at menu.
`
`pull medium A service that distributes information only when a user
`specifically makes a request. The Internet and its services, such as
`FTP, are pull media.
`
`pulse code modulation See PCM.
`
`push medium A service that distributes information by sending data
`to the user at a time determined by the server. The user may have
`signed up for a subscription service, in which case the server sends
`
`out information, such as stock quotes or news items, at intervals. Or,
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`query by example
`
`the user may be the recipient of unrequested email sent out by a
`spamming program.
`
`pushbutton See button (sense 1).
`
`push-pull Of or relating to an arrangement of two identical electronic
`devices that that are set in opposite phase in order to minimize
`distortion.
`
`[Q]
`
`QBE Abbreviation of query by example.
`
`QIC [kwik] Abbreviation ofquarter-inch cartridge. A tape cartridge
`in which the magnetic tape is V4 inch wide, used eSpecially for back-
`ups. Such cartridges may be the same size as standard cassette tapes
`or they may be miniature. The manufacturers of these tapes have
`established a set of standards for identifying and distinguishing
`their different sizes. See table at access time.
`
`quantum bit The smallest unit of information in a computer designed
`to manipulate or store information through effects predicted by quan-
`tum physics. Unlike bits in classical systems, a quantum bit has more
`than two possible states: a state labeled 0, a state labeled 1, and a
`
`combination of the two states that obeys the superposition principle.
`
`quarter-inch cartridge See QIC.
`
`qubit A quantum bit.
`
`qubyte A sequence of eight quantum bits operated on as a unit by a
`computer.
`
`query A request to a database for information. For example, if you
`have a database with the wholesale prices of widgets from every com-
`pany in the United States and the United Kingdom for every month
`from 1999 to 2009, you might send a query asking for a list of com-
`panies selling widgets in a certain price range in Ianuary 2000.
`
`query by example Abbreviated QBE A form of sending queries to a
`database in which the database management system gives a tem-
`
`plate With all the fields for the database. You then enter any restric-
`tions under the field to which they apply. For example, if your data-
`base has names, addresses, telephone numbers, and birthdays of
`your friends, you could type March in the birthday field to elicit a list
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`Facebook's Exhibit No. 1015
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`Snap's Exhibit No. 1015
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