Systems Architecture Chapter 5
CD-ROM
(computer science) memory whose contents can be accessed and read but cannot be changed
Access Time
(computer science) the interval between the time data is requested by the system and the time the data is provided by the drive
direct access
An access method that can access any storage location directly and in any order; primary storage devices and disk storage devices use random access.
random access
An access method that can access any storage location directly and in any order; primary storage devices and disk storage devices use random access...
parallel access
An access method that can access multiple storage locations simultaneously; can also be achieved by subdividing data items and storing the component pieces on multiple storage devices...
serial access
An access method that stores and retrieves data items in a linear (sequential) order; mainly used to hold backup copies of data stored on other storage devices...
Drive array
An arrangement of hard drives enclosed in a storage cabinet and accessed as though they're a single storage device
dual inline packages(DIPS)
An early form of packaging for RAM or ROM circuits; had two rows of electrical contact pins.
storage medium
A device or substance in a storage device that actually holds data...
DVD read-only memory (DVD-ROM)
A format for general-purpose read-only data storage on DVD.
nonvolatile memory (NVM)
A generic term for memory devices with long-term of permanent data retention...
linear recording
A geometric approach to recording data on a tape surface in which bits are placed along parallel tracks that run along the tape's entire length....
GST
A glasslike compound, used in phase-change memory, that can change between amorphous and crystalline states...
Linear Tape Open (LTO)
A magentic tape standard developed by Hewlett-Packard, IBM, and Seagate; uses linear recording and has technology improvements in tape cartridges, coercible materials, read/write heads/ and tape control....
hard disk
A magnetic disk medium with a rigid metal base (substrate) where data is recorded as patterns of magnetic charge...
Super Digital Linear Tape (SDLT)
A magnetic tape standard developed by Quantum Corporation; the cartridge has only one reel and the device records in parallel linear tracks in an end-to-end format...
Mammoth
A magnetic tape standard, developed by Exabyte, based on Digital Audio Tape; uses helical scanning and an improved tape drive technology to pack more data onto a single tape....
synchronous DRAM (SDRAM)
A read-ahead RAM that uses the same clock pulse as the system bus; read and write operations are broken into simple steps that can be completed in on bus clock cycle...
magnetic tape
A ribbon of plastic with a coercible (usually metallic oxide) coating, used to store data...
magneto-optical (MO) drive
A secondary storage device that uses a laser and reflected light to sense magnetically recorded bit values; data reading is based on the polarity of the reflected laser light, which is determined by the polarity of the magnetic charge...
double data rate (DDR)
A series of technologies, each doubling the data transfer rate of the previous synchronous DRAM version .
tape drive
A slow serial access device containing motors that wind and unwind tapes and read/write heads to access tape content...
single inline memory module (SIMM)
A small printed circuit board that incorporates multiple DIPs and has a row of electrical contacts on the edge; the entire package is designed to lock into a SIMM slot on a motherboard....
double inline memory module(DIMM)
A small printed circuit board that's essentially a SIMM with independent electrical contacts on both sides of the module.
solid state drive (SSD)
A storage device that mimics the behavior of a magnetic disk but uses flash RAM or other nonvolatile memory devices as the storage medium and read/write mechanism; expected to replaces magnetic disks gradually...
volatile
A term describing storage devices that CANNOT hold data for long periods; primary storage is usually volatile...
nonvolatile
A term describing storage devices that hold data without loss for long periods; secondary storage is usually nonvolatile...
dynamic RAM(DRAM)
A type of RAM that stores each bit by using a single transistor and capacitor...
electronically erasable programmable ROM(EEPROM)
A type of nonvolatile memory that can be programmed, erased and reprogrammed by signals sent from a CPU; the only type of ROM that's currently used...
erasable programmable ROM(EPROM)
A type of nonvolatile memory that's manufactured blank, written with a special EPROM writer and erased by exposure to ultraviolet light...
magnetoresistive RAM (MRAM)
A type of nonvolatile memory under development that stores bit values by using two magnetic elements, one with a fixed polarity and the other with polarity that changes when a bit is written; has better longevity than conventional flash RAM...
phase-change memory (PCM)
A type of nonvolatile memory under development that uses a GST compound capable of switching between amorphous and crystalline states; has fast write times and high longevity...
Digital Data Storage
Family of magnetic tape standards developed by Hewlett-Packard and Sony, and based on Digital Audio Tape. Uses Helical scanning
refresh cycle
In dynamic RAM, the period during which circuitry supplies fresh infusions of power automatically; read and write operations can't be performed during this cycle. Also refers to the transfer of a full screen of data from the display generator to the monitor....
core memory
In early computers, a technology for implementing primary storage as rings of ferrous materials embedded in a two-dimensional wire mesh.
platters
In magnetic disk media, they're flat, circular disks with metallic coatings that are rotated beneath read/write head; data is normally recorded on both sides...
cylinder
In magnetic disks, consists of all tracks at an equivalent distance from the edge or spindle on all platter surfaces.
Digital Audio Tape
Method of storing large amounts of data on tape using helical scan technology to write data at high densities across the tape at an angle.
disk defragmentation
Reorganizing data on a disk drive so that a file's contents are stored in sequential sectors, tracks, and platters; an OS utility is used to perform this task.
compact disk
an optical storage medium made of molded polymer for electronically recording, storing, and playing back audio, video, text, and other information in digital form; also CD-ROM, CD-R, CD-RW
firmware
Software, such as system BIOS, stored in nonvolatile memory; can be loaded into main memory at high speeds....
flash RAM
The most common type of nonvolatile memory; typically used to store firmware and in portable secondary storage systems, such as USB flash drives...
areal density
The number of bits per square inch of a disk platter.
coercivity
ability of an element or compound to accept and hold a magnetic charge
helical scanning
...A geometric approach to recording data on a tape surface in which data is read and written by rotating the read/write head at an angle and moving from tape edge to tape edge.
read/write head
...A mechanism in a storage device that reads and writes data to and from the storage medium; also referred to as a "read/write mechanism"
static RAM (SRAM)
...Atype of RAM that is implemented entirely with TRANSISTORS; the basic storage unit is a flip-flop circuit.
magnetic decay
...The tendency of magnetically charged particles to lose their charge over time; it's constant over time and proportional to the power of the chard.
head-to-head switching time
...The time needed to switch a hard drive's read/write circuitry to the correct read/write head before accessing a sector.
sequential access time
...The time required to read the second of two adjacent sectors on the same track and platter of a hard disk.
Quarter Inch Committee
A committee that develops open standards for magnetic tape drives on smaller computers...
DVD
AN optical disk format for distributing movies and other audiovisual content; stands for both "digital video disk" and "digital versatile disc"
track
One concentric circle of a platter; the surface area that passes under a read/write head when its position is fixed....
data transfer rate
The amount of data that a storage device can move from a storage medium to computer memory in one time unit, such as one second.
track-to-track (TTT) seek time
The average time needed to move a read/write head between two adjacent tracks. Measured in milliseconds...
fragmented
The condition of a hard disk with many programs and files scattered across it in non contiguous storage locations...
sector
The data transfer unit for magnetic disk and optical disc drives; the size is generally stated in bytes and can very from one device to another. Also refers to a fractional portion of a track on magnetic disk media...
read-only memory (ROM)
The earliest type of nonvolatile memory, with data content written permanently during manufacture; this primary storage device can be read, but no further data can be written...
sustained data transfer rate
The maximum data transfer rate a storage device or communication channel can sustain during lengthy data transfer operations...
magnetic leakage
The reduction in strength of a stored magnetic charge because of interference form adjacent magnetic charges of opposite polarity...
rotational delay
The time a hard disk controller must wait for the right sector to rotate beneath read/write heads...
Access Arm
device within a disk drive containing one or more read/write heads mounted at one end. The other end is attached to a motor that enables the read/write heads to be positioned over a single track of the disk platter
Advanced Intelligent Tape
magnetic tape standard developed by Sony based on Digital Audio Tape technology
average access time
statistical average (or mean) elapsed time required by a storage device to respond to a read or write command
