Disks And Secondary Storage

 Presentation by APPLE group.


The Benefits of Secondary Storage 

1. Tax records kept by the Internal Revenue Service or historical employee records kept by General Motors.
2. The record storage rooms would have to be enormous. 
3. Computers, in contrast, permit storage on tape or disk in extremely compressed form. 
4. Storage capacity is unquestionably one of the most valuable assets of the computer. 

Example Secondary storage:

• Magnetic Disk Storage
• Diskettes
• Hard Disks 
• Removable Storage: Zip Disks
• Optical Disk Storage
• DVDs 
• Magnetic Tape Storage 
• Backup Systems

The characteristics of the memory hierarchy that were described in 
the section on the CPU and memory :

Storage	Speed	Capacity	Relative Cost ($)	Permanent?
Registers	Fastest	Lowest	Highest	No
RAM	Very Fast	Low/Moderate	High	No
Floppy Disk	Very Slow	Low	Low	Yes
Hard Disk	Moderate	Very High	Very Low	Yes

Hard Disks 

• A hard disk is a metal platter coated with magnetic oxide that can be magnetized to represent data.
• different types of disk packs, with the number of platters varying by model. 
• Each disk in the pack has top and bottom surfaces on which to record data.
• Hard disk capacity for personal computers has soared in recent years, capacities of hundreds of megabytes are common and gigabytes are not unusual.
• Individual probably cannot imagine generating enough output-letters, budgets, reports, and so forth-to fill a hard disk, software packages take up a lot of space and can make a dent rather quickly.
• Graphics images and audio and video files require large file capacities. Perhaps more important than capacity, however, is the convenience of speed.
• Personal computer users find accessing files on a hard disk is significantly faster and thus more convenient than accessing files on a diskette.

Portable hard disk

External hard disk

Hard disk drive

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