LIS 505 - Storage
Devices for storing large amounts of data
in a relatively permanent form.
Also called secondary storage devices
or auxiliary storage devices.
The parts of a disk or tape drive
that read and write information on the medium.
Devices that read data from, and write data to, a disk.
Disks on which data are encoded
as tiny magnetic regions.
Soft, removable magnetic disks.
Also called diskettes or floppies.
Hard magnetic disks,
usually not easily removed
and faster and more capacious than floppy disks.
A single disk drive may contain several platters,
which look like a single disk to the software.
Serious disk drive malfunctions,
usually caused by a read-write head's scratching or burning a disk.
Short for Redundant Array of Independent
(or Inexpensive) Disks.
A method for using two or more disk drives in combination
to improve error recovery and speed.
Used on some servers.
A technique in which duplicate data are written to two disks simultaneously.
A technique in which data are broken up into units
which are spread across available disks.
Rings on disks or platters on which data can be written.
The smallest units that can be accessed on disks.
Portions of tracks.
Modern hard disks divide tracks into different numbers of sectors
depending on the radius of the track,
in a scheme called
or zone recording.
Sets of tracks on a single disk drive all with the same radius.
All the tracks that can be read
in a single position of the read-write heads.
Groups of one or more sectors assigned by an operating system.
The smallest units that can be assigned to a file.
Time taken to locate a piece of data
and make it available to a computer.
For a disk drive,
the portion of this time required to position the read-write heads
and latency (or rotational latency
or rotational delay)
is the additional time taken
for the right sector in the track to come under the read-write heads.
Speed at which data can be transferred.
Typically measured in megabytes per second for hard drives.
Disks read from (and sometimes written to) with lasers.
Short for compact disk - read-only memory.
A standard type of read-only optical disk
usually with a capacity of 650 megabytes.
A newer standard type of read-only optical disk
with a capacity of 4.7 gigabytes or higher.
Short for write-once read-many.
Short for compact disk - recordable.
A standard write-once read-many technology
compatible with CD-ROMs.
Short for compact disk - rewritable.
A standard write-many read-many technology,
compatible with CD-R
and partially with CD-ROMs.
Devices for writing to and reading from tapes.
A device that erases data on tapes before new data are written.
Long magnetically coated strips of plastic
on which data can be recorded.
magnetic tape or magtape.
with phonetic, pictographic, or ideographic meaning,
usually text elements (e.g., letters),
numerals, or punctuation marks.
A single character
may have a variety of different printed forms,
known as glyphs.
Characters are often equated with bytes;
but in Unicode
each character is represented by two bytes.
Divisions of records in database and similar files.
Typically, each field corresponds to an attribute
of an entity or
of a relationship between entities.
Divisions of database tables or files.
each record corresponds to an instance
of either a type of entity
or a type of relationship between entities.
Named collections of stored data.
A file may contain a program
or data to be used with one or more programs.
Collections of data organized so that their contents
(typically large and at least moderately complex)
can be accessed, managed, and updated easily.
In a database management system,
fields (or combinations of fields)
that can be used to sort records.
The primary key must have a unique value for each record;
a foreign key must correspond to a primary key in another set
of records in the database.
(For a more detailed comparison of file structures,
see LIS 558 - File structures.)
Organization of files for sequential access,
in which records are read or written in sequence,
from beginning to end.
Organization that allows random access,
reading or writing at any point in a file
by jumping directly to that point
without reading or writing intervening parts of the file.
Also called direct file organization.
Producing relatively small numeric values
from longer texts,
with the aim being to minimize cases where different texts
produce the same numeric value.
Useful for determining where to place and find records
in a random access file.
File organization including a list of keys,
each with a pointer to a corresponding record.
Processing in which the computer executes
a series of noninteractive tasks all at one time.
A typical batch process would involve
taking a master file
and applying a a transaction file
containing a list of changes
to create a new master file.
Processing in which the computer responds immediately
to user requests.
Last updated October 29, 2002.
This page maintained by
Prof. Tim Craven
E-mail (text/plain only): firstname.lastname@example.org
Faculty of Information and Media Studies
University of Western
Canada, N6A 5B7