The document discusses different types of secondary storage used in computer systems, focusing on magnetic disk storage. It describes diskettes and hard disks, the basic components and technologies used. Diskettes are flexible and store 1.44 MB or less, while hard disks are rigid platters that can store hundreds of gigabytes. Hard disks assemble multiple platters and use read/write heads to access and transfer data via tracks and sectors.

1. Chapter 6 B.M.H Storage and Multimedia

2. Index Secondary Storage Magnetic Disk Storage Diskettes Hard Disks Data Organization on a Disk

3. Computer System Hardware Input devices Output devices Processor and Memory Secondary Storages Software System SW Applications SW People

4. Computer system Input Processing Output Secondary Storage

5. Secondary Storage Benefits Space Reliability Convenience Economy

6. Secondary Storage Types Magnetic disk storage Diskettes, Hard Disks Magnetic tape storage Optical disk storage CD, DVD

7. Magnetic Disk Storage Magnetic media a technology of representing data as magnetized spots on the surface of a spinning disk A magnetized spot : 1 bit The absence of such a spot : 0 bit

8. Magnetic Disk Storage Reading data from the disk Converting the magnetized data to electrical impulses Writing data to disk Converting electrical impulses from the processor to magnetized spots on the disk

10. Magnetic Disk Storage Types Diskettes Hard disks

11. Diskettes Made of flexible Mylar Coated with iron oxide, a substance that can be magnetized Types The standard floppy disk : 3 1/2-inch diskette 1.44 megabytes of data Two new high-capacity drives : 120 or 200 megabytes per disk Iomega’s Zip drive : 250-megabyte disks Is not compatible with 31/2-inch diskettes

16. Hard Disk A rigid platter coated with magnetic oxide Sizes : various Capacity for PC Older ones : hundreds of megabytes New ones : tens of gigabytes of storage

17. Hard Disk Disk pack assembles several platters Components Platters Access arms Read/write heads

21. Hard Disks in Groups RAID ( R edundant A rray of I ndependent d isks) Uses a group of small hard disks that work together as a unit Used for storage system to be safe Types RAID level 1 Higher levels of RAID

22. Data organization on a disk Several characteristics Track Sectors Clusters Cylinder

29. Disk drive A device that allows data to be read from a disk or written to a disk The performance One measure : average access time Another measure : data transfer rate

31. Access Time The time needed to access data directly on disk Three primary factors Seek time Head switching Rotational delay Average access time Usually measured in milliseconds (ms) Current hard disk drives : Under 10ms

32. Data transfer The process of transferring data between memory and the place on the disk track Writing : from memory to the track Reading : from the track to memory Data transfer rate Tells how fast data can be transferred once it has been found Usually be measured in megabytes of data per second

33. Disk Cache Used to improve the effective access time Memory cache