Intel汇编语言程序设计(第五版)chapt_14.pptVIP

Assembly Language for Intel-Based Computers, 5th Edition Chapter 14: Disk Fundamentals Chapter Overview Disk Storage Systems File Systems Disk Directory Reading and Writing Disk Sectors (7305h) System-Level File Functions Disk Storage Systems Tracks, Cylinders, and Sectors Disk Partitions (Volumes) Tracks and Sectors Physical disk geometry - a way of describing the disk’s structure to make it readable by the system BIOS Track - concentric circle containing data Sector - part of a track Cylinders and Seeking Cylinder - all tracks readable from one head position Seek - move read/write heads between tracks Disk Formatting Physical formatting aka low-level formatting Usually done at the factory. Must be done before logical formatting Defines the tracks, sectors, and cylinders Logical formatting Permits disk to be accessed using sequentially numbered logical sectors Installs a file system (ex: NTFS) May install an operating system Fragmentation A fragmented file is one whose sectors are no longer located in contiguous areas of the disk. causes read/write heads to skip slower file access possible read/write errors Translation Translation - conversion of physical disk geometry to a sequence of logical sector numbers Performed by a hard disk controller (firmware) Logical sector numbers are numbered sequentially, have no direct mapping to hardware Disk Partitions Logical units that divide a physical hard disk Also called volumes Logical Partitions Created from an extended partition No limit on the number Each has a separate drive letter Usually contain data Can be bootable (ex: Linux) Disk Partition Table Located in the disks Master Boot Record (MBR), following a block of executable code Four entries, one for each possible partition Each entry contains the following fields: state (non-active, bootable) type of partition (BigDOS, Extended, . . .) beginning head, cylinder, sector numbers ending head, cylinder, sector numbers offset of partition from MBR number of sectors