1 / 16

Section 13.2 – Secondary storage management (Former Student’s Note)

Section 13.2 – Secondary storage management (Former Student’s Note). Index. 13.2 Disks 13.2.1 Mechanics of Disks 13.2.2 The Disk Controller 13.2.3 Disk Access Characteristics. Disks:.

fitzgerald-gardner
Download Presentation

Section 13.2 – Secondary storage management (Former Student’s Note)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Section 13.2 – Secondary storage management(Former Student’s Note)

  2. Index • 13.2 Disks • 13.2.1 Mechanics of Disks • 13.2.2 The Disk Controller • 13.2.3 Disk Access Characteristics

  3. Disks: • The use of secondary storage is one of the important characteristics of a DBMS, and secondary storage is almost exclusively based on magnetic disks: Use Example 13.1

  4. Structure of a Disk

  5. Data in Disk • 0’s and 1’s are represented by different patterns in the magnetic material. • A common diameter for the disk platters is 3.5 inches.

  6. Mechanics of Disks • Two principal moving pieces of hard drive 1- Head Assembly 2- Disk Assembly • Disk Assembly has 1 or more circular platters that rotate around a central spindle. • Platters are covered with thin magnetic material

  7. Top View of Disk Surface

  8. Mechanics of Disks • Tracks are concentric circles on a platter. • Tracks are organized into sectors which are segments of circular platter. • Sectors are indivisible as far as errors are concerned. • Blocks are logical data transfer units.

  9. Disk Controller • Control the actuator to move head assembly • Selecting the surface from which to read or write • Transfer bits from desired sector to main memory

  10. Simple Single Processor Computer

  11. Disk Access characteristics • Seek time: The disk controller positions the head assembly at the cylinder containing the track on which the block is located. The time to do so is the seek time. The force to move disk controller is about 5g (gravitational force) • Rotational latency: The disk controller waits while the first sector of the block moves under the head. This time is called the rotational latency.

  12. Disk Access characteristics • Transfer time: All the sectors and the gaps between them pass under the head, while the disk controller reads or writes data in these sectors. This delay is called the transfer time. • Latency of the disk: The sum of the seek time, rotational latency, transfer time is the latency of the time.

  13. Disks: • Example 13.1 Megatron 747 • 16 surfaces • 216 tracks per surfaces • 28 (average) sectors per track • 212 bytes per sector • 1 mega bytes per track

  14. Disks: • Example 13.1 • Megatron 747 Disk • If blocks are 214 bytes or 16384 bytes, then one block uses 4 consecutive sectors, and there are (on the average) 32 blocks per track.

  15. Disks: • Example 13.2 • The disk rotates at 7200 rpm; i.e., it makes one rotation in 8.33 millisecond. • To move the head assembly between cylinders take one millisecond to start and stop. Plus one millisecond for every 4000 cylinders traveled. Thus the head moves one track in 1.00025

  16. Disks: • Example 13.2 milliseconds and move from the innermost to outermost track, a distance of 65, 536 tracks, in about 17.38 millisecond • Gaps occupy 10% of the space around a track. • Take two rotations to read whole track

More Related