Section 13.2 – Secondary storage management

Index 13.2 Disks Mechanics of Disks The Disk Controller Disk Access Characteristics

Mechanics of Disks 2 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

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.

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

Disk Storage characteristics Rotation speed Number of platters per unit Number of tracks per surface Number of bytes per track

Disk Access characteristics Seek time Rotational latency Transfer time

Writing blocks almost same as reading blocks For modifying, blocks need to be loaded into main memory and re-written to disk.