Database System: Chapter 9 - Disk Storage and Indexing Structures for Files presents about Disk Storage Devices (Preferred secondary storage device for high storage capacity and low cost, Data stored as magnetized areas on magnetic disk surfaces,.), Files of Records, Indexing Structures for Files. | Chapter 9 Disk Storage and Indexing Structures for Files Copyright © 2004 Pearson Education, Inc. 5/14/2020 4:10:15 AM Outline Disk Storage Devices Files of Records Indexing Structures for Files Slide 9 - Disk Storage Devices (cont.) Preferred secondary storage device for high storage capacity and low cost. Data stored as magnetized areas on magnetic disk surfaces. A disk pack contains several magnetic disks connected to a rotating spindle. Disks are divided into concentric circular tracks on each disk surface. Track capacities vary typically from 4 to 50 Kbytes. Slide 9 - Disk Storage Devices (cont.) Because a track usually contains a large amount of information, it is divided into smaller blocks or sectors. The division of a track into sectors is hard-coded on the disk surface and cannot be changed. One type of sector organization calls a portion of a track that subtends a fixed angle at the center as a sector. A track is divided into blocks. The block size B is fixed | Chapter 9 Disk Storage and Indexing Structures for Files Copyright © 2004 Pearson Education, Inc. 5/14/2020 5:23:41 AM Outline Disk Storage Devices Files of Records Indexing Structures for Files Slide 9 - Disk Storage Devices (cont.) Preferred secondary storage device for high storage capacity and low cost. Data stored as magnetized areas on magnetic disk surfaces. A disk pack contains several magnetic disks connected to a rotating spindle. Disks are divided into concentric circular tracks on each disk surface. Track capacities vary typically from 4 to 50 Kbytes. Slide 9 - Disk Storage Devices (cont.) Because a track usually contains a large amount of information, it is divided into smaller blocks or sectors. The division of a track into sectors is hard-coded on the disk surface and cannot be changed. One type of sector organization calls a portion of a track that subtends a fixed angle at the center as a sector. A track is divided into blocks. The block size B is fixed for each system. Typical block sizes range from B=512 bytes to B=4096 bytes. Whole blocks are transferred between disk and main memory for processing. Slide 9 - Disk Storage Devices (cont.) Slide 9 - Disk Storage Devices (cont.) A read-write head moves to the track that contains the block to be transferred. Disk rotation moves the block under the read-write head for reading or writing. A physical disk block (hardware) address consists of a cylinder number (imaginery collection of tracks of same radius from all recoreded surfaces), the track number or surface number (within the cylinder), and block number (within track). Reading or writing a disk block is time consuming because of the seek time s and rotational delay (latency) rd. Double buffering can be used to speed up the transfer of contiguous disk blocks. Slide 9 - Disk Storage Devices (cont.) Slide 9 - Records Fixed and variable length records Records contain fields which have values of a particular type (., .
