Module 7.pptx for most important for air

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1. External Storage Devices

2. Consider a disk pack with the following specifications- 16 surfaces, 128 tracks per surface, 256 sectors per track and 512 bytes per sector. What is the capacity of disk pack? What is the number of bits required to address the sector? If the diameter of innermost track is 21 cm, what is the maximum recording density?

3. Capacity of disk pack = Total number of surfaces x Number of tracks per surface x Number of sectors per track x Number of bytes per sector = 16 x 128 x 256 x 512 bytes = 2 28  bytes = 256 MB

4. Total number of sectors = Total number of surfaces x Number of tracks per surface x Number of sectors per track = 16 x 128 x 256 sectors = 2 19  sectors Thus, Number of bits required to address the sector = 19 bits

5. Storage capacity of a track = Number of sectors per track x Number of bytes per sector = 256 x 512 bytes = 2 8  x 2 9  bytes = 2 17  bytes = 128 KB   Circumference of innermost track = 2 x π x radius = π x diameter = 3.14 x 21 cm = 65.94 cm   Now, Maximum recording density = Recording density of innermost track = Capacity of a track / Circumference of innermost track = 128 KB / 65.94 cm = 1.94 KB/cm

6. RAID Redundant Array of Independent Disks

7. What is RAID? Stands for Redundant Array of Independent (Inexpensive) Disks. It’s a technology that enables greater levels of performance, reliability and/or large volumes when dealing with data. How?? By concurrent use of two or more ‘ hard disk drives’. How Exactly?? Mirroring, Stripping (of data) and Error correction techniques combined with multiple disk arrays give you the reliability and performance.

8. RAID flavors Commonly used ones: RAID 0 RAID 1 RAID 5 RAID 10 Other types used…but rarely: RAID 2,3,4,6,50……

9. RAID 0 analysis Performance: The fragments are written to their respective disks simultaneously on the same sector. This allows smaller sections of the entire chunk of data to be read off the drive in parallel, hence good performance.

10. RAID 1 RAID1 is ‘data mirroring’. Two copies of the data are held on two physical disks, and the data is always identical. Twice as many disks are required to store the same data when compared to RAID 0. Array continues to operate so long as at least one drive is functioning.

11. Performance: If we use independent disk controllers for each disk, then we can increase the read or write speeds by doing operations in parallel.

12. RAID 2

13. RAID 10 Combines RAID 1 and RAID 0. Which means having the pleasure of both - good performance and good failover handling. Also called ‘Nested RAID’.

14. What’s happening present day? RAID 6: It is seen as the best way to guarantee data integrity as it uses double parity. It has a drawback though of longer write time.

15. Key Board & Display Interface SCOPE,VIT Chennai

16. Cont… The interface consists of the following registers Data register (DATAIN & DATAOUT) Status Register consists of single bit status flag (SIN,SOUT,DIRQ,KIRQ) Control Register SCOPE,VIT Chennai

17. Cont.. SIN flag represents keyboard status SIN flag set to 1 when key is pressed(data is ready) and it get reset when the processor had read the data SOUT flag represents display status Similar to SIN flag KIRQ ,DIRQ flag bits represent the interrupt to the processor( if 1 interrupt request is send to the processor, after the processor service the interrupt request it get reset) by the Keyboard and Display respectively DEN,KEN are control flag bits used to enable and disable the display and the keyboard respectively SCOPE,VIT Chennai

18. Performance S equential read, sequential write, random read, random write, power consumption, responsiveness Disk Performance: Seek time is the time taken for a hard disk controller to locate a specific piece of stored data. Rotational latency: wait for desired sector to pass under the head. One-half disk rotation on average (4ms @ 7500RPM) Transfer: read or write one or more sectors as they pass under the head. Typical transfer rates: 100-150 MBytes /sec. Latency refers to the sum of seek time plus rotational latency; typically 5-10ms. RAID: Read/write speed Mean Time Between Failure (MTBF): On average how long until system breaks.

19. Assume 1010110 is transmitted as 1000110 Use hamming code to detect error