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AirPort: AirPort is Apple's name for the IEEE 802.11 wireless networking standard. The original AirPort based on the 802.11b standard has a maximum transmission speed of 11 Mbps. The newer AirPort protocols are based on the 802.11g standard with a maximum speed of 54 Mbps and the 802.11n standard with a maximum speed of 248 Mbps.

Allocation Block: The space on a volume is allocated as a group of consecutive sectors called an allocation block.

Allocation File: This file in the volume structures keeps track of the blocks that are used and those that are free.

AltiVec: AltiVec is a technology built into most PowerPC processors that provides increased performance for certain types of high-bandwidth data processing functions.

Apple Sound Chip: The Apple Sound Chip, or ASC, is a custom manufactured sound chip made for Apple by Sony. Often referred to as a DAC, or Digital to Analog Converter, the ASC provides the Macintosh with advanced sound creation capabilities.

ASC: See Apple Sound Chip.

ASCII: American Standard Code for Information Interchange. A numeric ID assigned to every number, letter, or other symbol that enables different programs and different computers to consistently share information. The standard code consists of an 8-bit coded number.

AT Attachment Packet Interface: This is an interface, commonly known at ATAPI, between the computer and attached CD-ROM drives and tape backup drives. ATAPI adds additional commands to the IDE interface (see IDE/ATA below) needed for controlling CD-ROM and tape players. ATAPI is part of the Enhanced IDE (EIDE) interface, also known as ATA-2.

AT Attachment Standard: This is a standard electronic interface, commonly called ATA or IDE, between a computer and its mass storage devices that specify how peripherals communicate with the computer.

The following chart shows the maximum data transfer rate for the various ATA versions:

ATA (original) 4 Mb/sec

ATA-2 16.6 Mb/sec

ATA-3 16.6 Mb/sec

ATA-4 (Ultra ATA/33) 33.3 Mb/sec

ATA-5 (Ultra ATA/66) 66.6 Mb/sec

ATA-6 (Ultra ATA/100) 100.0 Mb/sec

ATA: See AT Attachment Standard.

ATAPI: See AT Attachment Packet Interface.

Attributes File: This file in the volume structures, if present, tracks the attributes of a file—such as whether the file is locked or not.

Backup: An exact copy of computer information. In case of data loss or corruption, the original data can be retrieved from the backup.

Benchmark Test: In a given configuration, the test used to evaluate the performance of computer software and hardware.

Bit: A bit is the smallest unit of information that can be stored by a computer. It is represented as a zero or a one.

Booting: The term booting originated from bootstrap. It is the process by which the computer starts itself and reads the Operating System. When you boot from a CD you are starting and reading the OS from the CD.

Bundle Bit: A bundle bit is a resource located in most Macintosh applications. If active, it indicates that the file contains icon information.

Bus: A bus is the path that transmits information between a computer and connected devices. An example is the USB bus, which connects the computer to USB devices such as keyboards and mice.

Byte: A byte is a unit of information stored in the computer. A byte consists of eight bits. An ASCII character consists of one byte.

Cache: A high-speed intermediate buffer memory that lies between the processor and main memory in the computer's memory hierarchy. It can reduce memory access time.

Catalog File: The Catalog File is a part of the Volume Structures. It keeps track of the files and folders on a volume.

Central Processor Unit: The Central Processor Unit or Main Processor Unit is a chip that maintains the processing and sequencing facilities for machine-related functions such as initial program booting and instruction execution.

Chip: A "chip," or Integrated Circuit, is a miniature electronic component with specialized functions within the computer.

Circuit: A conductor through which an electric current can flow; the entire course traversed by an electric current. Parts and components assembled to function together in an electric or electronic device or system.

Clump: The file system attempts to provide allocation blocks for a file in a fixed size group called a clump.

Contiguous: Joining or touching in a continual, consecutive, unbroken order to a common edge or boundary.

CPU: See Central Processing Unit.

CRT: CRT is an acronym for cathode Ray tube. It is the element that produces the image on most computer and television screens.

Device: A device is any piece of equipment that can be attached to a computer. These might include a monitor, disk drive, printer, etc. Devices are also known as peripherals.

DIMM: See Dual Inline Memory Module.

Directory: Another term for the volume structures.

Disk: A disk is a flat circular device for storing computer data. The data might be stored magnetically or optically. The most common disks are CD-ROM disks made of stiff, translucent plastic.

Disk Drive: A device for controlling and accessing data stored on a disk or disk stack.

Disk Driver: A driver for a block transfer device (see Driver below) such as a hard disk drive, floppy drive, or CD-ROM drive. It is a software plug-in that implements a hardware abstraction layer for the device.

Drive: A drive is a computer peripheral that stores data. It might use a tape cartridge, a disk, or other medium. A drive may be "read only" or "read/write."

Driver: A driver (or device driver) is software that lets a computer communicate with a device such as a printer, hard drive, etc. When you purchase a new device, its driver is usually provided as part of the software that comes with it.

Driver Descriptor Map: The Driver Descriptor Map holds information about the number and location of drivers on a disk.

Dual Inline Memory Module: A DIMM, or Dual Inline Memory Module, is a memory unit used by the computer. It contains RAM chips mounted on a small printed circuit board that plugs into DIMM slots making for easy installation and removal.

EIDE: See Enhanced Integrated Drive Electronics.

Enhanced Integrated Drive Electronics: This is a standard electronic interface, commonly called EIDE, between a computer and its mass storage devices. EIDE is an enhancement to IDE (see below) which makes it possible to address a hard drive larger than 528 MB. It also provides faster access to the hard drive, support for Direct Memory Access (DMA), and support for additional drives, including CD-ROM drives and tape drives.

Ethernet: A popular networking protocol originally developed at Xerox. Standard ethernet communicates at 10Mbps and fast ethernet communicates at 100Mbps or 1 GB.

Extents File: This file in the volume structures contains the extent data for the volume. Extents are the separate components of a fragmented file.

File System: Every volume uses a file system to organize the information it stores. A file system keeps track of where files are located on the volume. The Macintosh typically uses either the HFS or HFS+ filing system.

FireWire: FireWire is Apple's name for the high speed IEEE 1394 bus standard. It can handle data rates of up to 400Mbps and is commonly used to connect hard drives and video cameras to the Macintosh. The newer IEEE 1394b specification, which Apple calls FireWire 800, handles data rates of 800Mbps.

Firmware: This is software that has been permanently recorded into ROM (Read Only Memory). It is a cross between hardware and software.

GB: See Gigabyte.

Gigabyte: A Gigabyte consists of 1,024 Megabytes.

Head: A mechanism that reads, writes, or erases data on a storage medium.

Head Crash: A Head Crash refers to contact between a read/write head and a floppy or a hard disk surface. This usually results in damage to the disk surface and loss of data.

HFS: HFS stands for Hierarchical Filing System and is also known as Macintosh OS Standard Format. It is a method of formatting storage devices for Macintosh computers.

HFS+: Macintosh OS Extended Format is a method of formatting storage devices attached to Macintosh computers. Compared to the earlier HFS it supports more files and increases the efficiency of storage on larger drives.

I/O: An acronym for input/output.

IDE: See Integrated Device Electronics.

IEEE: See Institute of Electrical and Electronics Engineers.

Initialize: Initialization is a process of preparing a storage medium to hold data. During initialization, the volume structures for a volume are created specifying locations for storing data. Initialization erases directory information. However; the data in files themselves may be left on the volume.

Institute of Electrical and Electronics Engineers: Often referred to as IEEE (I-triple-E), this is a professional organization that sets many standards used in the computer and electronics industries. For example, AirPort is another name for the IEEE 802.11b networking standard.

Integrated Device Electronics: This is a standard electronic interface, commonly called IDE, between a computer and its mass storage devices. IDE devices (sometimes called ATA devices) conform to the ATA (AT Attachment Standard, see reference earlier in the Glossary) which specifies how peripherals communicate with the computer.

Journaling: Journaling is a feature available for HFS+ volumes under Mac OS X 10.2.2 and above. If journaling is enabled on a volume then the file system maintains a transaction log of reads and writes. This makes the file system more robust and helps protect against data loss in the event of an unexpected shutdown.

Kb: Kilobit or 1024 bits.

KB: Kilobyte or 1024 bytes.

Kbps: Kilobits per second.

KBps: Kilobytes per second.

LAN: See Local Area Network.

Local Area Network: A Local Area Network, or LAN, consists of a group of computers and peripherals in close proximity that have been set up so that they can communicate with one another. Macintosh computers usually connect via Ethernet or LocalTalk.

Logic Board: The logic board is the main component of any computer system. It might even be called the brain of the computer since it contains all the parts necessary to perform the many calculations that computers perform. This is where the CPU, the memory, and the main components of the computer are located.

Logical Unit Number: The SCSI bus identification number.

Low-Level Format: Low-level formatting removes and then recreates the markers that organize the data on a drive. All data on the drive is usually erased. Low-level formatting is usually followed by initializing.

LUN: See Logical Unit Number.

MAC address: see Media Access Control address.

Mb: See Megabit.

Mbps: Megabits per second.

MB: See Megabyte.

MBps: Megabytes per second.

MHz: See Megahertz.

Media Access Control address: The Media Access Control address, or MAC address, of an ethernet interface is a unique 48-bit address that is encoded directly into the ethernet adapter hardware by the manufacturer. It consists of 6 hexadecimal numbers separated by colons. For example: 00:00:c0:34:f1:52.

Megabit: A unit of measure for storage capacity. One megabit is equivalent to 1,048,576 bits.

Megabyte: A unit of measure for storage capacity. One megabyte is equivalent to 1,048,576 bytes.

Megahertz: A measure of frequency—one million cycles per second.

Mount Point: The mount point of a volume is the location in the directory hierarchy that the volume appears. The volume appears as a sub-directory of the mount point. In Mac OS X this is typically /Volumes.

OS: OS stands for Operating System. This is the software that allows you to interact with your computer and that keeps track of files, peripherals, programs, networks, etc.

Parallel: Parallel, the converse of serial, is a method of transmitting simultaneous bits of information over a multi-paired connector. This is much faster than serial communication since multiple bits of data can be transmitted at once. The SCSI port is a parallel port.

Partition: Disks contain sections called partitions. A partition is a block of addresses on a drive that the disk driver assigns to a specific volume.

Partition Map: The partition map holds information about the start, length, and type of each partition on a disk.

Parameter RAM: Also called PRAM. This is a dedicated chip that holds information that is vital to the Macintosh computer. A battery supplies power to the PRAM so that when the Macintosh is shut down it will retain this information. Information contained in this chip includes keyboard settings, mouse settings, and the startup device.

PCI: The standard bus on the newer Macintosh computers. It supersedes NuBus.

PRAM: See Parameter RAM.

PRAM Battery: The PRAM battery is a 3 to 4 1/2 volt battery that supplies the parameter RAM chip with power once the Macintosh has been turned off.

Protocol: A set of rules that dictate the operations of computers to allow them to communicate.

Quartz Extreme: Quartz Extreme is the name for enhanced graphics routines (such as high quality animations) that Apple added in Mac OS X 10.4. It is supported by the video subsystem on faster G4 and later Mac models. The Graphics/Displays area of System Profiler will indicate whether or not the computer supports Quartz Extreme.

RAID: See Redundant Array of Independent Disks

RAM: See Random Access Memory.

Random Access Memory: RAM is an acronym for Random Access Memory. This is memory that stores the data and programs used by your computer. Its contents are lost when the computer is turned off. RAM generally comes in packages called DIMMs and SIMMs.

Read Only Memory: ROM is dedicated chips that permanently store information. In the Macintosh the chips contain operational routines that the computer employs. ROM does not lose its information when the power is turned off. The information is permanent and cannot be changed.

Redundant Array of Independent Disks: Usually referred to as RAID. RAID software allows multiple physical hard drives to be combined so as to appear as one or more volumes. This allows for faster and/or more reliable disk access. The most common RAID standards are RAID0 (or striped) where data is distributed in parallel across multiple drives for increased speed and RAID1 (or mirrored) where the same data is written simultaneously to multiple drives for reliability.

Refresh Rate: This is the rate at which an image is repeated on a display surface such as a monitor.

Resolution: A measurement of the sharpness of an image; either by the number of pixels or the number of lines and columns on the display screen.

RGB: RGB is a video format standing for Red, Green and Blue providing color images on a CRT. By combining different levels of the red, green, and blue signals almost any color can be displayed on a monitor.

ROM: See Read Only Memory.

Root Directory: The top level of a volume's directory. It may contain subdirectories (otherwise known as folders).

SCC: See Serial Communication Controller.

SCSI: See Small Computer System Interface.

SCSI Chip: The SCSI Chip allows the Macintosh to communicate with SCSI devices. Most Macintosh computers equipped with SCSI use the 8530 SCSI chip.

SCSI Conflict: A SCSI Conflict occurs when two or more SCSI devices share the same ID number on the same bus. This can keep the devices from working reliably or from working at all.

Sector: A Sector is a portion of a disk drive's track and typically contains 512 bytes of data.

Self-Monitoring Analysis and Reporting Technology: .This is a technology built into most modern hard drives. It is an industry standard that employs predictive diagnostics and analysis to help foresee a drive failure BEFORE it happens.

Serial: Serial is a communication format for sending information in consecutive bits of data, in contrast to parallel in which multiple bits of data are sent simultaneously. The advantage of using this format is that it requires less data lines, usually two, whereas parallel can require up to 50.

Serial Communication Controller: The Serial Communication Controller or SCC is an integrated circuit that supervises all serial processing on the Macintosh.

Small Computer System Interface: Also known as SCSI, this is a parallel interface standard that specifies how peripherals communicate with the computer. There are several varieties of SCSI. The transfer rate for standard SCSI built into SCSI-equipped Macs is 4MBps. The maximum rate for SCSI is 80MBps.

SIMM: See Single Inline Memory Module.

Single Inline Memory Module: A SIMM, or Single Inline Memory Module, is a memory unit used by the computer. It contains RAM chips mounted on a small printed circuit board that plugs into SIMM slots allowing for easy installation and removal.

S.M.A.R.T: see Self-Monitoring Analysis and Reporting Technology

Startup File: This file in the volume structures, if present, contains information used by the ROM to determine what program will boot the computer.

Termination: A technique of capping the end of a signal bus to prevent resonance from occurring within a signal. A SCSI bus requires a terminator at each end.

USB: USB or Universal Serial Bus is a medium speed protocol for connecting devices to a computer. It has superseded ADB on Macintosh computers. USB is hot-swappable and has a maximum transfer rate of 12Mbps. The new USB 2.0 standard has a raw data rate at 480Mbps.

Versatile Interface Adapter: Versatile Interface Adapter or VIA is an integrated circuit used to control user input on the Macintosh. The VIA is attached to the ADB circuitry, as well as the NuBus, to control signal timing.

Volume: A volume refers to a logical storage unit seen by the computer as a single item. This may be a floppy disk, an entire hard drive, or one or more partitions on hard drives. Although a partition is typically seen as one volume, a RAID volume may consist of more than one partition on more than one drive.

Volume Header: This portion of the volume structures contains important data about the volume as a whole. Included is the volume name, number of files and folders, and amount of free space.

Volume Structures: A collection of data structures on a volume that is used by the file system to organize the storage of data on the volume. They include the Volume Header and Catalog.

VRAM: VRAM, or Video RAM, is the memory that holds the information that is displayed on your computer's screen.