Magnetic Disks (Cont.) Disk controller-interfaces between the computer system and the disk drive hardware. accepts high-level commands to read or write a sector initiates actions such as moving the disk arm to the right track and actually reading or writing the data 。 Computes and attaches checksums to each sector to verify that data is read back correctly If data is corrupted,with very high probability stored checksum won't match recomputed checksum Ensures successful writing by reading back sector after writing it Performs remapping of bad sectors Database System Concepts-7th Edition 12.8 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 12.8 ©Silberschatz, Korth and Sudarshan th Edition Magnetic Disks (Cont.) ▪ Disk controller – interfaces between the computer system and the disk drive hardware. • accepts high-level commands to read or write a sector • initiates actions such as moving the disk arm to the right track and actually reading or writing the data • Computes and attaches checksums to each sector to verify that data is read back correctly ▪ If data is corrupted, with very high probability stored checksum won’t match recomputed checksum • Ensures successful writing by reading back sector after writing it • Performs remapping of bad sectors