Track (moving medium)
A track is a path on a recording medium. There are some variations in nomenclature; for some media a track is a logical (content based) path and for others it is based on the geometry of the medium. The term is not used for punched cards.
Content-based tracks
The terms session, title or track may be used, depending on the medium.
LP
A track on a long playing record (LP) is a segment of the spiral groove recording a single movement, song or other work. Usually, unrecorded sections of the groove guide the tone arm between consecutive tracks. However occasionally - for example on some language learning records - the tracks are not connected, and the tone arm must be moved manually to the next track's lead-in groove.
Optical disks
A track, session or title on an audiovideo optical disk is a segment recording a single movement, song or other work.
Geometry-based tracks
On some devices a track is defined based on the geometry of the medium, typically running for the full length or circumference.
Linear
On magnetic cards, magnetic strips and tape, tracks normally[a] run the full length of the medium. Some devices record multiple tracks in parallel either to improve speed or to provide separate channels for, e.g., stereophonic sound.
Punched tape
On Punched tape, also known as paper[b] tape, a track runs the length of the tape and all tracks are recorded in parallel. References to the number of tracks sometimes use the word channel or level. Five level tape is used for Baudot, eight-level for ASCII and twelve level for carriage control tapes.
Magnetic tape reels and cartridges
On analog audio tape, a track runs the length of the tape and typically contains a single channel; stereophonic and quadraphonic recording use multiple tracks.
On digital tape, a track runs the length of the tape; typically all tracks are written and read in parallel.
Magnetic cards and strips
On magnetic cards[c] and magnetic strips used as storage media, a track runs the length of the card or strip; typically multiple tracks are written and read in parallel and considered to be a single logical track.
Magnetic stripe cards
Magnetic stripe cards are commonly used as credit cards, identity cards, and transportation tickets. Standardized cards contain up to three parallel tracks. Unusually, two different recording densities are used (210 and 75 bits per inch).
The NCR CRAM and RCA Model 3488 Random Access Computer Equipment used magnetic cards in a magazine (deck for CRAM).
The IBM 2321 Data Cell[1] used magnetic strips in a cell and subcell. The tracks had variable length count key data (CKD) records.
Helical scan
On some videotape and magnetic tape media, a read/write head moves across the width of the tape while the tape is moving, providing a diagonal Helical scan. An example is the IBM 3850 Mass Storage System (MSS).
Rotating
A track[d] on a rotating magnetic disk or drum normally[e] runs for the circumference of the medium. All tracks on a magnetic drum have the same capacity.
Early rotating drives recorded bits at a constant angular density and all tracks had the same data capacity. On all contemporary disk drives a track contains fixed length sectors. However, some older disks and drums recorded variable length records, and the DASD subsystems supported for general use by IBM's flagship operating systems simulate the Count Key Data (CKD) organization.
The first disk drive, the 1957 IBM 350 disk storage, had ten 100 character sectors per track; the tracks on contemporary disk drives are substantially larger.
In the early days of the industry sectors were referred to by several other names.
Drums
All tracks on a rotating drum have the same data capacity. Early drums were used for main memory, and tracks were divided into fixed length words, typically 36 bits[3] for use on binary computers and ten digits plus sign[4] for use on decimal computers. Drums used for auxiliary storage typically had fixed length sectors, but the IBM 7320[5] on the IBM 7090 and 7094 had variable length records controlled by a format track and the IBM 2301,[6] 2303[7] and 7320[8] on the S/360 had variable length CKD records.
Disks
The first disk drive, the 1957 IBM 350 disk storage, had ten 100 character sectors per track and recorded at a constant angular density; the tracks on contemporary disk drives are substantially larger and are recorded at a constant linear density, so that outer tracks contain more data than inner tracks. Most of the industry designed disk drives with fixed length sectors, however the IBM 1301 and IBM 1302 on the 7000 series had variable length records controlled by format tracks and all DASD on S/360 had variable length CKD records. Although IBM supports FBA and SCSI disk drives on IBM Z, its flagship z/OS operating system only has limited support for SCSI drives and requires CKD drives for most functions.
Virtual Geometry
Starting with the 3350, IBM offered disc drives with new geometries that could present the appearance of older disk drives. At the present time almost all IBM mainframes use DASD subsystems that look like 3390 drives but use SCSI disks and SSDs to actually store the data.
Notes
- ^ But see Helical scan.
- ^ The term paper tape was often used to refer to perforated Mylar tape.
- ^ Not to be confused with magnetic stripes on, e.g., credit cards.
- ^ Sometimes called a band.
- ^ The RCA Data Record File[2] (DRF) used a spiral track.
References
- IBM2301
- IBM System/360 Component Descriptions -- 2820 Storage Control and 2301 Drum Storage (PDF) (Third ed.), IBM, September 1968, A22-6895-2
- IBM2841-0
- IBM System/360 Component Descriptions 2841 Storage Control Unit 2302 Disk Storage Models 3 and 4 2311 Disk Storage Drive 2321 Data Cell Drive, Model 1 7320 Drum Storage (PDF), IBM, A26-5988-0
- IBM2841-7
- IBM System/360 Component Descriptions - 2841 and Associated DASD (PDF) (Eighth ed.), IBM, December 1969, GA26-5988-7
- ^ IBM2841-0, pp. 37-40, IBM 2321 Data Cell Drive.
- ^ RCA 301 Electronic Data Processing System Programmers' Reference Manual (PDF), April 1960, p. 7, 93-16-000
- ^ The UNIVAC Scientific General Purpose Computer System (Model 1103A) PRELIMINARY INFORMATION (PDF), Remington Rand, 1 December 1955
- ^ "Storage" (PDF). IBM 650 magnetic drum data-processing machine manual of operation (PDF). 1955. p. 7. 22-6060-2.
- ^ IBM 7090/7094 Data Processing Systems IBM 7320 Drum Storage (PDF), IBM, 1962, G22-6717
- ^ IBM2301, pp. 30-31, IBM 2301 Drum Storage.
- ^ IBM2841-7, pp. 73-76, IBM 2303 Drum Storage.
- ^ IBM2841-0, pp. 41-42, IBM 7320 Drum Storage.