1. RAID
1.1. RAID Level 0
1.1.1. A disk array can provide high i/o execution rates by balancing the i/o load across multiple disks
1.2. RAID Level 1
1.2.1. Provides real-time copy of all data
1.3. RAID Level 2
1.3.1. The number of redundant disks is proportional to the log of the number data disks
1.4. RAID Level 3
1.4.1. In a transaction-oriented environment performance suffers
1.5. RAID Level 4
1.5.1. Involves a write penalty when an i/o write request of small size is performed
1.6. RAID Level 5
1.6.1. A typical allocation is a round-robin scheme
1.7. RAID Level 6
1.7.1. Two different parity calculations are carried out and stored in separate blocks on different disks
2. Optical Memory
2.1. Compact Disk (CD)
2.1.1. Write-once read-many
2.2. Digital Versatile Disk (DVD)
2.2.1. The DVD has replaced the videotape used in video cassete recorders (VSRs) and replace the CD-ROM in personal computers and servers
2.3. High-Definition Optical Disk
2.3.1. Designed to store high-definition videos and to provide significantly greater storage capacity compared to DVDs
3. Magnetic Tape
3.1. Tape systems use the same reading anf recording techniques as disk systems
4. Magnetic Disk
4.1. Read and Write Mechanism
4.1.1. Write : Current through coil produces magnetic field , Pulses sent to head, Magnetic pattern recorded on surface below.
4.1.2. Read ( Traditional)
4.1.3. Read (Contemporary)
4.2. Data Organization and Formatting
4.2.1. The head is a relatively small device capable of reading from or writing to a portion of the platter rotating beneath it.
4.2.2. Gives rise to the organization of data on platter in a concentric set of rings called tracks
4.2.3. Each track is the same width as the head. There are thousands of tracks per surface.
4.3. Physical Characteristics
4.3.1. Fixed-head disk
4.3.1.1. One read-write head per track
4.3.1.2. Heads mounted on a fixed ridged arm that extends across all tracks
4.3.2. Movable-head disk
4.3.2.1. One read-write head
4.3.2.2. Head is mounted on an arm
4.3.2.3. The arm can be extended or retracted
4.3.3. Non-removable disk
4.3.3.1. Permenantly mounted in the disk drive
4.3.3.2. The hard disk in a personal computer is a non-removable disk
4.3.4. Removable disk
4.3.4.1. Can be removed and replaced with another disk
4.3.4.2. A disk may be moved from one computer system to another
4.3.4.3. Floppy disks and ZIP cartridge disks are examples of removable disks
4.3.5. Double sided disk
4.3.5.1. Magnetizable coating is applied to both sides of the platter
4.4. Disk Performance Parameters
4.4.1. Relational delay (rotational latency)
4.4.1.1. The time it takes for the beginning of the sector to reach the head
4.4.2. Access time
4.4.2.1. The sum of the seek time and the rotational delay
4.4.2.2. The time it takes to get into position to read or write
4.4.3. Transfer time
4.4.3.1. Once the head is in position, the read or write operation is then performed as the sector moves under the head
4.4.3.2. This is the data transfer portion of the operation