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2. Ministry of Higher Education Course: File organization- INF 221
Higher Technological Institute
Computer Science Department
Second Year
Sheet 3: Secondary Storage Devices Theoretical
1. Classify types of storage devices?
There are two major types of storage devices:
1. Directed Access Storage Devices (DASDs)
• Magnetic disks
• Harddisks (high capacity, low cost per bit)
2. Optical Disks
 CD-ROM,DVD-ROM(Read-noly/write-once, holda lot of data, cheap)
 Serial Devices
 Magnetic Tapes
2. Describe in details the simplified structure of a disk with drawing?
3. What is meaning of internal fragmentation, FAT, extent and cluster?
Internal fragmentation: occurs when the memory is distributed into fixed-sized blocks.
File Allocation Table (FAT): is a file system that was developed by Microsoft to support small disks
and simple folder structures.
Cluster: is a group of two or more computers, or nodes, that run in parallel to achieve a common
goal.
Extent: is a contiguous area of storage reserved for a file in a file system, represented as a range of
block numbers, or tracks on count key data devices.

3. 4. Describe in details Redundant Array of Independent Disks?
The answer is In the Report
5. State the main drawbacks of tapes and draw tape organization architecture?
 They are sequential access devices.
 We must esstially step through all the data in order.
 Can’t directly access a given location on tape.
 Mostly used to back up operational data periodically.
6. Compare between disks and tapes?
DISK TAPE
Random access Sequential access
Immediate access Long-term storage
Expensive seek in sequential processing No seek in sequential processing
7. Compare between CD and DVD?
CD DVD
Laser-Beam Infrared light (780nm) Red light(635-650nm)
Capacity maximum 680MB Maximum 17GB (25 times of CD
Reference Speed 1.2/sec. CLV 4.0/sec. CLV
8. Describe in details dual layer disc?
The dual layer disc is a parallel track path (for computer CD-ROM use), Direction: same for both layers.
It’s direction: is opposite directions; since the refence beam and angular velocities are the same at the layer
transition point, the delay comes from refocusing. This permits seamless transition for movie playback.
Programs
9. If we have fixed length records and number of records =50000 records when size of record =256
bytes, how many cylinders are needed if the disk characteristics as the following:
• Number of bytes per sector = 512
• Number of sectors per track = 63
• Number of tracks per cylinder = 16
• Number of cylinders = 4092

4. 10. How many records can be stored per track for the following blocking factors?
• Block factor = 10 Block factor = 60
If Disk characteristics and File Characteristics
• Block-addressable Disk Drive
• Size of track = 20.000 bytes
• Nondata overhead per block = 300 bytes
• Record size = 100 bytes
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