MECH 2301 Lecture Notes - Lecture 29: Disk Partitioning
22 May 2018
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MECH 2301 Lecture 29 Notes
Introduction
Linked allocation and the file allocation table method
• At first it would seem that the system could simply place link pointers to the next block
at the end of every file block.
• However, placing link pointers within the file blocks themselves is impractical
• It would be necessary to read each block from the beginning of the file, in sequence, to
obtain the location of its succeeding block.
• This method would therefore be slow, awkward, and unsuitable for relative access files,
where it is desirable to read or write only blocks containing relevant data.
• A somewhat more practical method is to store the pointers as linked lists within a table.
• Windows still makes this available for small disks and solid-state storage devices
• Such as low-capacity flash drives and floppy disks
• When this method is used, Windows provides a single table on each disk or disk
partition
• Since these systems allow a disk to be divided into partitions on the system
• This table is called a file allocation table or FAT.
• Each file allocation table holds the link pointers for every file stored on the particular
disk or disk partition.
• These file allocation tables are copied to memory at system boot time or, in the case of
removable devices, mount time, and remain in memory as long as the file system is
active.
• The FAT method is illustrated
• It will help to follow the trail i the diagra as you read this descriptio.
• The directory for each file contains an entry that points to the first block of the file.
• Each entry in the FAT corresponds to a block or cluster on the disk.
• Each entry contains the link pointer that points to the next block in the file.
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