Assembly Language for Intel-Based Computers, 5th Edition.ppt

1、Assembly Language for Intel-Based Computers, 5th Edition,Chapter 14: Disk Fundamentals,(c) Pearson Education, 2006-2007. All rights reserved. You may modify and copy this slide show for your personal use, or for use in the classroom, as long as this copyright statement, the authors name, and the tit

2、le are not changed.,Slide show prepared by the author Revision date: June 4, 2006,Kip R. Irvine,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,2,Chapter Overview,Disk Storage Systems File Systems Disk Directory Reading and Writing Disk Sectors (7305h) System-Level File Functio

3、ns,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,3,Disk Storage Systems,Tracks, Cylinders, and Sectors Disk Partitions (Volumes),Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,4,Tracks and Sectors,Physical disk geometry - a way of describing the disks s

4、tructure to make it readable by the system BIOS Track - concentric circle containing data Sector - part of a track,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,5,Cylinders and Seeking,Cylinder - all tracks readable from one head position Seek - move read/write heads between

5、tracks,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,6,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 us

6、ing sequentially numbered logical sectors Installs a file system (ex: NTFS) May install an operating system,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,7,Fragmentation,A fragmented file is one whose sectors are no longer located in contiguous areas of the disk. causes read/

7、write heads to skip slower file access possible read/write errors,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,8,Translation,Translation - conversion of physical disk geometry to a sequence of logical sector numbers Performed by a hard disk controller (firmware) Logical sect

8、or numbers are numbered sequentially, have no direct mapping to hardware,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,9,Disk Partitions,Logical units that divide a physical hard disk Also called volumes,Primary partition Up to four permitted Each may boot a different OS,Exte

9、nded partition Maximum of one permitted May be divided into multiple logical partitions, each with a different drive letter,Primary and Extended Up to three primary and one extended,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,10,Logical Partitions,Created from an extended p

10、artition No limit on the number Each has a separate drive letter Usually contain data Can be bootable (ex: Linux),Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,11,Disk Partition Table,Located in the disks Master Boot Record (MBR), following a block of executable code Four ent

11、ries, 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 in the partition,

12、See also: Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,12,Cascading Partition Tables,Boot, BigDOS,NA, Extended,NA, BigDOS,NA, BigDOS,Drive D,Drive E,Primary partition,links to,Boot = bootable (system) NA = non active BigDOS = over 32 MB,Logical partitions (D, E),Drive C,Irvine, Kip

13、 R. Assembly Language for Intel-Based Computers 5/e, 2007.,13,Dual-Boot Example,System 98 and Win2000-A are bootable partitions One is called the system partition when active,DATA_1 and BACKUP are logical partitions Their data can be shared by both operating systems,Irvine, Kip R. Assembly Language

14、for Intel-Based Computers 5/e, 2007.,14,Master Boot Record (MBR),The MBR contains the following elements: Disk partititon table A program that jumps to the boot sector of the system partition,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,15,Whats Next,Disk Storage Systems Fil

15、e Systems Disk Directory Reading and Writing Disk Sectors (7305h) System-Level File Functions,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,16,File Systems,Directory, File, Cluster Relationships Clusters FAT12 FAT16 FAT32 NTFS Primary Disk Areas,Irvine, Kip R. Assembly Langua

16、ge for Intel-Based Computers 5/e, 2007.,17,File System,This is what it does for you: Keeps track of allocated and free space Maintains directories and filenames Tracks the sector location of each file and directory,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,18,Directory, F

17、ile, Cluster, Sector Relationships,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,19,Cluster (1 of 2),Smallest unit of space used by a file Consists of one or more adjacent sectors Size depends on both the type of file system in use and the disk partition size A file is a link

18、ed sequence of clusters. Example:,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,20,Cluster (2 of 2),A file always uses at least one cluster A high percentage of space may be wasted Example: 8,200-byte file requires three 4K clusters:,Irvine, Kip R. Assembly Language for Intel

19、-Based Computers 5/e, 2007.,21,FAT12,Designed for diskettes Each FAT entry is 12 bits Very little fault tolerance two copies of the FAT (cluster table) Optimal storage for small files 512-byte clusters,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,22,FAT16,MS-DOS format for h

20、ard disks 16-bit FAT entries Large cluster size when disk 1 GB inneficient for small files Max 2 GB size under MS-DOS Little or no recovery from read/write errors,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,23,FAT32,Supports long filenames Supported by all version of MS-Win

21、dows from Windows 95 onward (except Windows NT) 32-bit FAT entries 32 GB maximum volume size Improved recovery from read/write errors,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,24,NTFS,Supported by Windows NT, 2000, and XP Handles large volumes can span multiple hard drive

22、s Efficient cluster size (4K) on large volumes Unicode filenames Permissions on files & folders Share folders across network Built-in compression and encryption Track changes in a change journal Disk quotas for individuals or groups Robust error recovery Disk mirroring,Irvine, Kip R. Assembly Langua

23、ge for Intel-Based Computers 5/e, 2007.,25,Primary Disk Areas,A disk or volume is divided into predefined areas and assigned specific logical sectors. Example: 1.44 MB diskette Boot record (sector 0) File allocation table (sectors 1 18) Root directory (sectors 19 32) Data area (sectors 33 2,879),Irv

24、ine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,26,Your turn . . .,1. A 1.44 MB diskette has 512 bytes per cluster. Suppose a certain file begins in cluster number 5. Which logical disk sector contains the beginning of the file? (Hint: see page 503).,2. Suppose a certain hard driv

25、e has 4 KB per cluster, and we know that the data area begins in sector 100. If a particular file begins in cluster 10, which logical sectors are used by the cluster?,(answers on next panel . . .),Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,27,Answers,1. The data area begin

26、s in Sector 33 (see page 503). Each cluster = 1 sector, so the file begins in sector 33 + 5 = sector 38.,2. The hard drive has 8 sectors per cluster. The starting cluster number of the file is 100 + (8 * 10) = 180. Therefore, sectors 180 187 are used by the files first cluster.,Irvine, Kip R. Assemb

27、ly Language for Intel-Based Computers 5/e, 2007.,28,Boot Record (1 of 2),Fields in a typical MS-DOS boot record: Jump to boot code (JMP instruction) Manufacturer name, version number Bytes per sector Sectors per cluster Number of reserved sectors (preceding FAT #1) Number of copies of FAT Maximum nu

28、mber of root directory entries Number of disk sectors for drives under 32 MB Media descriptor byte Size of FAT, in sectors Sectors per track,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,29,Boot Record (2 of 2),(continued) Number of drive heads Number of hidden sectors Number

29、 of disk sectors for drives over 32 MB Drive number (modified by MS-DOS) Reserved Extended boot signature (always 29h) Volume ID number (binary) Volume label File-system type (ASCII) Start of boot program and data,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,30,Whats Next,Di

30、sk Storage Systems File Systems Disk Directory Reading and Writing Disk Sectors (7305h) System-Level File Functions,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,31,Keeping Track of Files,MS-DOS Directory Structure Long Filenames in MS-Windows File Allocation Table,Irvine, Ki

31、p R. Assembly Language for Intel-Based Computers 5/e, 2007.,32,MS-DOS Directory Structure (1 of 2),Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,33,MS-DOS Directory Structure (2 of 2),Time field equals 4DBDh (9:45:58), and the Date field equals 247Ah (March 26, 1998). Attribu

32、te is normal:,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,34,Date and Time Fields,Date stamp field:Time stamp field:,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,35,Your turn . . .,What time value is represented here?,Irvine, Kip R. Assembly Languag

33、e for Intel-Based Computers 5/e, 2007.,36,File Attribute Values,What type of file has attribute 00100111 . . . ?,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,37,Long Filenames in MS-Windows,Filename: ABCDEFGHIJKLMNOPQRSTUV.TXT,Irvine, Kip R. Assembly Language for Intel-Based

34、 Computers 5/e, 2007.,38,File Allocation Table (1 of 2),A map of all clusters on the disk, showing their ownership by specific files Each entry corresponds to a cluster number Each cluster contains one or more sectors Each file is represented in the FAT as a linked list, called a cluster chain. Thre

35、e types of FATs, named after the length of each FAT entry: FAT-12 FAT-16 FAT-32,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,39,File Allocation Table (2 of 2),Each entry contains an n-bit integer that identifies the next entry. (n=12,16, or 32) Two cluster chains are shown i

36、n the following diagram, one for File1, and another for File2:,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,40,Whats Next,Disk Storage Systems File Systems Disk Directory Reading and Writing Disk Sectors (7305h) System-Level File Functions,Irvine, Kip R. Assembly Language fo

37、r Intel-Based Computers 5/e, 2007.,41,Reading and Writing Disk Sectors (7305h),INT 21h, Function 7305h (absolute disk read and write) Reads and writes logical disk sectors Runs only in 16-bit Real-address mode Does not work under Windows NT, 2000, or XP Tight security!,Irvine, Kip R. Assembly Langua

38、ge for Intel-Based Computers 5/e, 2007.,42,DISKIO Structure,Used by Function 7305h:,DISKIO STRUCTstartSector DWORD 0 ; starting sector numbernumSectors WORD 1 ; number of sectorsbufferOfs WORD buffer ; buffer offsetbufferSeg WORD DATA ; buffer segment DISKIO ENDS,Irvine, Kip R. Assembly Language for

39、 Intel-Based Computers 5/e, 2007.,43,Example,.data buffer BYTE 512 DUP(?) diskStruct DISKIO .codemov ax,7305h ; absolute Read/Writemov cx,0FFFFh ; always this valuemov dl,3 ; drive Cmov bx,OFFSET diskStruct mov si,0 ; read sectorint 21h,Example: Read one or more sectors from drive C:,Irvine, Kip R.

40、Assembly Language for Intel-Based Computers 5/e, 2007.,44,Sector Display Program,Pseudocode: Ask for starting sector number and drive number do while (keystroke ESC)Display headingRead one sectorIf MS-DOS error then exitDisplay one sectorWait for keystrokeIncrement sector number end do,View the sour

41、ce code,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,45,Whats Next,Disk Storage Systems File Systems Disk Directory Reading and Writing Disk Sectors (7305h) System-Level File Functions,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,46,System-Level File

42、 Functions,Common Disk-Related Functions Get Disk Free Space Create Subdirectory Remove Subdirecrory Set Current Directory Get Current Directory,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,47,Common Disk-Related Functions,Irvine, Kip R. Assembly Language for Intel-Based Com

43、puters 5/e, 2007.,48,ExtGetDskFreSpcStruc Structure (1 of 2),StructSize: A return value that represents the size of the ExtGetDskFreSpcStruc structure, in bytes. Level: Always 0. SectorsPerCluster: The number of sectors inside each cluster. BytesPerSector: The number of bytes in each sector. Availab

44、leClusters: The number of available clusters. TotalClusters: The total number of clusters in the volume.,Structure data returned by Fucntion 7303h:,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,49,ExtGetDskFreSpcStruc (2 of 2),AvailablePhysSectors: The number of physical sect

45、ors available in the volume, without adjustment for compression. TotalPhysSectors: The total number of physical sectors in the volume, without adjustment for compression. AvailableAllocationUnits: The number of available allocation units in the volume, without adjustment for compression. TotalAlloca

46、tionUnits: The total number of allocation units in the volume, without adjustment for compression. Rsvd: Reserved member.,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,50,Function 7303h Get Disk Free Space,AX = 7303h ES:DI points to a ExtGetDskFreSpcStruc CX = size of the Ext

47、GetDskFreSpcStruc variable DS:DX points to a null-terminated string containing the drive name,View the DiskSpc.asm program,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,51,Create Subdirectory,.data pathname BYTE “ASM“,0.codemov ah,39h ; create subdirectorymov dx,OFFSET pathna

48、meint 21hjc DisplayError. DisplayError:,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,52,Remove Subdirecrory,.data pathname BYTE C:ASM,0.code mov ah,3Ah ; remove subdirectorymov dx,OFFSET pathnameint 21hjc DisplayError. DisplayError:,Irvine, Kip R. Assembly Language for Intel

49、-Based Computers 5/e, 2007.,53,Set Current Directory,.data pathname BYTE “C:ASMPROGS“,0.codemov ah,3Bh ; set current directorymov dx,OFFSET pathnameint 21hjc DisplayError. DisplayError:,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,54,Get Current Directory,.data pathname BYTE 64 dup(0) ; path stored here by MS-DOS.codemov ah,47h ; get current directory pathmov dl,0 ; on default drivemov si,OFFSET pathname int 21hjc DisplayError. DisplayError:,Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007.,