Disk Drive Schematic Disk Drive Schematic Typically 512 bytes - PowerPoint PPT Presentation

Disk Drive Schematic Disk Drive Schematic Typically 512 bytes Typically 512 bytes reads by sensing a magnetic field spare sectors added for fault tolerance spare sectors added for fault tolerance writes by creating one floats on air cushion created by data on a track data on a track Track Block/Sector Track Block/Sector spinning disk can be read can be read without moving without moving s–1 s–1 0 0 arm arm 1 1 Head track skewing 2 track skewing 2 staggers logical staggers logical address 0 on address 0 on ... ... Cylinder adjacent one to adjacent one to account for time account for time 17 18 Arm to move head to move head assembly Surface Platter Spindle set of tracks on different surfaces with same track index thin cylinder that holds magnetic material 2018: 4200-15000 RPM each platter has two surfaces Disk Read/Write Disk Read/Write Present disk with a sector address Present disk with a sector address Old: CHS = (cylinder, head, sector) Old: CHS = (cylinder, head, sector) New abstraction: Logical Block Address (LBA) New abstraction: Logical Block Address (LBA) linear addressing 0...N-1 linear addressing 0...N-1 Heads move to appropriate track Heads move to appropriate track seek seek (and though shalt approximately find) settle settle (fine adustments) Disk access time: Disk access time: Appropriate head is enabled Appropriate head is enabled Wait for sector to appear under head Wait for sector to appear under head seek time + rotational latency rotational latency Read/Write sector Read/Write sector transfer time transfer time

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