Storage Structure
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Moving-head Disk Mechanism
Magnetic Tape
•Early secondary-storage medium of choice
•Persistent, inexpensive, and has large data capacity
•Very slow access due to sequential nature
•Used for backup and for storing infrequently-used data
•Kept on spools
•Transfer rates comparable to disk if read write head is positioned to the data
•20-200GB are typical storage capacities
The storage device used by a computer to hold the currently executing program and its working data. A modern computer's main memory is built from random access memory integrated circuits. In the old days ferrite core memory was one popular form of main memory, leading to the use of the term "core" for main memory.
Magnetic Disk 
The primary computer storage device. Like tape, it is magnetically recorded and can be re-recorded over and over. Disks are rotating platters with a mechanical arm that moves a read/write head between the outer and inner edges of the platter's surface. It can take as long as one second to find a location on a floppy disk to as little as a couple of milliseconds on a fast hard disk. See hard disk for more details.
Moving-head Disk Mechanism
The moving head disc control unit can be connected to either a DMC or DMA channel and each control unit supports up to 4 to 8 disc spindles (unit 0 .. 7).
Hardware and programming details for each type can be found in the Honeywell document: "Honeywell Series 16 Moving Head Disk Options 4623, 4651 and 4720 programmers' reference manual".
A driver is made for the 4651 to test the moving head logic as implemented by the SIMH H316 simplator. The driver supports multiple units and is designed for a control unit connected to the Multiplexer (channel 0 is used). Drive constants are defined as parameters, so it should be not too complex to change the driver for another disc type. SIMH + driver are tested with a testprogram.
Before the disc software can be used, a disc pack must be defined and formatted. A disk pack can be formatted with geometric or sequential sector addresses. The driver currently is designed for the use of sequential addresses. The other parameter to choose with formatting is the sector length. For the test is chosen for a sector length of 128 words (which provided 12 secros per track).
Disk Structure :
•Cylinder: the set of tracks that all the heads are currently located at.
•Track: A ring on a disk where data can be written
•Sector: The smallest transfer unit of data accessed in a block
•Cluster: A group of sectors the operating system treats as a unit
•Organization Choices
–Sector mapping (One dimension array of logical blocks)
•0 is sector z, track 0 of the outermost cylinder.
•Subsequent sectors map through tracks, through cylinders, in an inner to outer direction.
–Sector counts and density
•fixed sectors per track with varying densities
•more sectors for the outer tracks with constant density
–Bad block management
•Sector sparing: replace bad sectors with spares in the same cylinder
•Sector slipping: copy all sectors down to the next spare
Hardware and programming details for each type can be found in the Honeywell document: "Honeywell Series 16 Moving Head Disk Options 4623, 4651 and 4720 programmers' reference manual".
A driver is made for the 4651 to test the moving head logic as implemented by the SIMH H316 simplator. The driver supports multiple units and is designed for a control unit connected to the Multiplexer (channel 0 is used). Drive constants are defined as parameters, so it should be not too complex to change the driver for another disc type. SIMH + driver are tested with a testprogram.
Before the disc software can be used, a disc pack must be defined and formatted. A disk pack can be formatted with geometric or sequential sector addresses. The driver currently is designed for the use of sequential addresses. The other parameter to choose with formatting is the sector length. For the test is chosen for a sector length of 128 words (which provided 12 secros per track).
Disk Structure :
•Cylinder: the set of tracks that all the heads are currently located at.
•Track: A ring on a disk where data can be written
•Sector: The smallest transfer unit of data accessed in a block
•Cluster: A group of sectors the operating system treats as a unit
•Organization Choices
–Sector mapping (One dimension array of logical blocks)
•0 is sector z, track 0 of the outermost cylinder.
•Subsequent sectors map through tracks, through cylinders, in an inner to outer direction.
–Sector counts and density
•fixed sectors per track with varying densities
•more sectors for the outer tracks with constant density
–Bad block management
•Sector sparing: replace bad sectors with spares in the same cylinder
•Sector slipping: copy all sectors down to the next spare
Magnetic Tape
Magnetic tape is a medium for magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of plastic. Nearly all recording tape is of this type, whether used for recording audio or video or for computer data storage. It was originally developed in Germany, based on the concept of magnetic wire recording. Devices that record and playback audio and video using magnetic tape are generally called tape recorders and video tape recorders respectively. A device that stores computer data on magnetic tape can be called a tape drive, a tape unit, or a streamer.
Magnetic tape revolutionized the broadcast and recording industries. In an age when all radio (and later television) was live, it allowed programming to be prerecorded. In a time when gramophone records were recorded in one take, it allowed recordings to be created in multiple stages and easily mixed and edited with a minimal loss in quality between generations. It is also one of the key enabling technologies in the development of modern computers. Magnetic tape allowed massive amounts of data to be stored in computers for long periods of time and rapidly accessed when needed.
Today, many other technologies exist that can perform the functions of magnetic tape. In many cases these technologies are replacing tape. Despite this, innovation in the technology continues and tape is still widely used.
Magnetic tape revolutionized the broadcast and recording industries. In an age when all radio (and later television) was live, it allowed programming to be prerecorded. In a time when gramophone records were recorded in one take, it allowed recordings to be created in multiple stages and easily mixed and edited with a minimal loss in quality between generations. It is also one of the key enabling technologies in the development of modern computers. Magnetic tape allowed massive amounts of data to be stored in computers for long periods of time and rapidly accessed when needed.
Today, many other technologies exist that can perform the functions of magnetic tape. In many cases these technologies are replacing tape. Despite this, innovation in the technology continues and tape is still widely used.
•Early secondary-storage medium of choice
•Persistent, inexpensive, and has large data capacity
•Very slow access due to sequential nature
•Used for backup and for storing infrequently-used data
•Kept on spools
•Transfer rates comparable to disk if read write head is positioned to the data
•20-200GB are typical storage capacities
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