1. Indira Gandhi National Open University presents

2. A Video Lecture Course: Computer Platforms

3. BACKING STORAGE AND INTERFACING

4. Objectives zDefine some backing storage technologies zDiscuss about the storage formats zDiscuss about the head mechanism of hard disks zDefine some of the interfacing mechanisms for backing storage

5. What is Magnetic Disk? zA circular metal or plastic coated with magnetisable material zA mechanism using conducting coil which reads/write on disk: called head zConcentric tracks with width same as the head size

6. Disk-data layout

7. Why does Gap exist between adjacent tracks? To minimise errors due to Misalignments To minimise interference of magnetic fields

8. zThe track on outermost side has same number of bits as the innermost track. zDensity per linear inch increase as we move from outer to inner track REASON: SIMPLE ELECTRONICS

9. Data are stored in block-size region called SECTORS –Typically 10-100 sectors/track –To avoid unnecessary precision requirements on system, adjacent sectors are separated by intra track gaps

10. How are sector position within a track identified? Control data for recording start and end of each sector and starting position on a track Example, 600 bytes are used for storing 512K data

11. Head Motion: Fixed head - one/track. Moveable head (one per surface) Disk portability : Non removable/ Removable Sides : Single/Double Platter : Single/ Multiple Some Characteristics of Disks

12. Head Mechanism Contact (Floppy) Fixed gap Aerodynamic gap (Winchester)

13. R A I D (Redundant Array of Independent Disks) A set of physical disk drives viewed as a single logical drive Data is distributed across the physical drives of an array Redundant disk capacity is used to guarantee data recoverability in case of a disk failure

14. Optical Memory CD-ROM WORMs Erasable Optical Disks

15. CD-ROMs

16. Appropriate for distribution of large amount of data to a large number of users High information storage capacity Mass replication is inexpensive Removable disks thus may be used for archival storages

17. Disadvantages: Once fabricated cannot be changed Higher access time than disk

18. WORMs Applicable for applications when small number of copies of a set of data is needed Disk can be written by a special writer once only WORMs are useful for archival storage of documents

19. Erasable Optical Disk Can be read or written just like magnetic disk Technology is magnetic-optical system High Capacity Portable disks Reliable disks Use formats same as that of Hard disk

20. Some Newer Storage Technologies ZIP Drives A high capacity floppy disk drive developed by Image Corporation Hold about 100 MB of data Inexpensive and Durable Useful as a popular backing storage media Useful for transporting large files

21. Digital Video Disks A new type of CD-ROMs Have a capacity of 4.7 GB to 17 GB Store movie date in MPEG-2 format Smaller and easier to store and durable Better picture quality and alternate sound Tracks

22. Interfacing storage devices to The Computer Why I/O Interfaces needed? For coordinating the flow of data between Internal resources and external devices Data buffering : To cater for the speed differences between the storage devices & CPU Error detection

23. Communicates with System through System or I/O bus Communicates with devices The Interface

24. What is ESDI? Enhanced Small Device Interface (ESDI) an interface standard for connecting disk drives to PCs. ESDI controllers are needed to use ESDI disks

25. What is IDE and Enhanced IDE? An interface for mass storage devices The controller is integrated into the disk or the drive Intelligent Electronics or Integrated Device Electronics

26. EIDE supports data rate between 4 Mbps to 16.6 Mbps three to four time faster then IDE EIDE can support mass storage up to 8.4 GB whereas IDE was up to 528 MB

27. What is UDMA? Supports data transfer rates of 33.3 Mbps Twice as fast as previous disk standards for PCs

28. SUM UP: The secondary storage technologies such as disks, CD- ROMs The data format of disks & CD- ROMs Head mechanisms for disks The interface standards for storage devices