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EXTERNAL MEMORY - Coggle Diagram
EXTERNAL MEMORY
MAGNETIC DISK
Circular platter constructed of nonmagnetic material called, the substrate, coated with magnetizable material.
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Physical Characteristics
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Non-removable Disk
Permanently mounted in the disk drive. The hard disk in a personal computer is a non-removable disk.
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Disk Classification
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Winchester Heads
Designed to operate closer to the disk's surface fro allowing greater data density. Used a sealed drive assemblies.
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RAID
Raid Level 4
Make use of independent access technique. The data stripping is used. To calculate the new parity the new array management software must read the old user strip and the old parity strip.
Raid Level 2
Makes uses for parallel access technique. Spindles of the individual drives are synchronized so that each disk head is in the same position on each disk at any given time
Raid Level 5
Most secured Raid level. It required at least 3 drives but can work with up to 16. RAID-5 is good all-round system that combines efficient storage with excellent security and decent performance. It is ideal for file and application servers that have limited number of data drives.
Raid Level 1
Mirroring. Data are stored twice by writing them to both the data drive and a mirror drive. Need at least 2 drives for RAID 1 array. RAID-1 ideal for mission critical storage, for instance for accounting system. It also suitable for smaller server in which only two data drives will be used.
Raid Level 6
RAID-6 is like RAID-5 but the parity data are written to two drives. RAID-6 is good all-round system that combines efficient storage with excellent secutiry and decent performance. It is preferable over RAID 5 in the file and application servers that use many large drives for data storage.
Raid Level 0
Striping. System data are split up into blocks that get written across all the drives in the array. The performances can be enhanced further by using multiple-controllers, ideally one controller per disk. Ideal for non-ideal storage of data that have to be read/written at high speed
Raid Level 3
Requires only single redundant disk no matter how large the disk array. Can achieve very high data transfer rates
OPTICAL MEMORY
Compact Disk (CD-ROM)
Disk Read Only Memory. A non erasable disk used or storing computer data. The standard system uses 12 CM disks and can hold more than 650 MBytes.
CD
A compact disk. A non erasable disk that stores digitized audio information. The standard system uses 12 CM disks & can record more than 60 minutes of uninterrupted playing time.
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DVD
Digital Versatile Disk. A technology for producing digitized, compress representation of video information. Both 8 and 12 CM diameters are used, with a double speed capacity of up to 17 GBytes.
DVD-R
DVD-Recordable. Similar to DVD-ROM. The user can write to the disk only once. Only one-sided disk can be used.
DVD-RW
DVD Rewritable. Similar to a DVD-ROM. The user can erase and rewrite to the disk multiple times. Only one-sided disk can be used.
Blu-Ray DVD
High definition video disk. Provides considerably greater data storage density than DVD. Using a 450-nm (blue violet) laser. A single layer on a single side can store 25 GBytes.
MAGNETIC TAPE
The system use the same reading & recording technique as disk system. The medium is flexible polyester tape coated with magnetizable material. Data on tape are structured as a number of parallel tracks running lengthwise. The data are read and written in contiguous blocks called physical recorded. Blocks on the tape are separated by gaps referred to as inter-recorded gaps.