BITS Pilani Pilani Campus Pawan Sharma Lecture ES C263 INSTR/CS/EEE F241 Microprocessor Programming and Interfacing

BITS Pilani, Pilani Campus  Secondary Storage Last Lecture

BITS Pilani, Pilani Campus  Disk Organization  Interpretation of Boot sector  Root Directory  File Allocation Table  Example Today’s Lecture

BITS Pilani, Pilani Campus  Logical sector 0 known as the boot sector, contains all the critical information regarding the disk medium’s characteristics.  The first byte in this sector should be a jump instruction.  The first byte should be either a intra-segment jump JMP or a short jump JMP  The final component of the boot sector is bootstrap. Boot Sector

BITS Pilani, Pilani Campus Interpretation of Boot sector bytes

BITS Pilani, Pilani Campus Contd……

BITS Pilani, Pilani Campus Logical interpretation boot sector of a formatted floppy

BITS Pilani, Pilani Campus Logical partition of a MS-DOS disk (1.44MB floppy disk)

BITS Pilani, Pilani Campus  DOS keeps track of each file and subdirectory as they are added to the disk by user  Every time user adds a file DOS updates directory area  name of the file  time and date of creation  length of file  Files names are limited to eight characters and a three character extension Root Directory

BITS Pilani, Pilani Campus Root directory taken from a floppy

BITS Pilani, Pilani Campus Root Directory

BITS Pilani, Pilani Campus ASCII Table

BITS Pilani, Pilani Campus BITInterpretation 0Read only file 1Hidden file 2System file 3Volume label 4Directory 5Archive bit 6Reserved 7reserved Attribute Byte Interpretation

BITS Pilani, Pilani Campus

Name of the file: CAP Extension: Attributes: Volume label and Archive bits set Next 10 bytes are reserved. Time of creation: 23::13::00 Date of creation: March 8, Starting cluster no: 0 File size: 0 bytes Root Directory Interpretation

BITS Pilani, Pilani Campus  Purpose – create disk space for files  Contains entry for each cluster  Contains information of the group of clusters that are assigned to the file  Fields in FAT gives the cluster number that is allocated to file  The entries in the positions 0 and 1 of the FAT are reserved. It is the entry 2 of the FAT that contains the description of the physical sector no. ???? File Allocation Table

BITS Pilani, Pilani Campus File Allocation Table

BITS Pilani, Pilani Campus Each group of three consecutive bytes contains two 12-bit entries, arranged as follows: The first byte contains the eight least significant bits of the first entry. The four least significant bits of the second byte contain the four most significant bits of the first entry. The four most significant bits of the second byte contain the four least significant bits of the second entry. The third byte contains the eight most significant bits of the second entry. In other words, if UV, WX and YZ are the hexadecimal representations of the three consecutive bytes, then the entries are XUV and YZW, respectively. Interpreting FAT

BITS Pilani, Pilani Campus FD FF FF FF 4F 00 FF 8F F0 FF 09 A0 00 0B E0 00 FFD FFF FFF 004 FFF FFF A 00B 00E Interpreting the File Allocation Table

BITS Pilani, Pilani Campus

1362 bytes OrCIM.tXT Read only, system file, Archived 09hrs:46min:08sec 0FH or (15d) C