1. File Systems

2. Linked block allocation Each block contains a header with –Number of bytes in the block –Pointer to next block Blocks need not be contiguous Files can expand and contract Seeks can be slow First block … Head: 417... Length Byte 0 Byte 4095... Length Byte 0 Byte 4095... Length Byte 0 Byte 4095... Block 0Block 1Block N-1

3. DOS - Fat file system Disk Block File Descriptor Disk Block Disk Block … 43 107 254 The actual Table Disk Block Disk Block Disk Block … 43 107 43 254 … File Descriptor Logical view Physical view

4. Indexed Files Extract headers and put them in an index Simplify seeks May link indices together (for large files) Index block … Head: 417... Byte 0 Byte 4095... Byte 0 Byte 4095... Byte 0 Byte 4095... Block 0 Block 1 Length

5. Index Structures Index Files Data Files max key 200 400 600 234234 50 100 150 200 12341234 250 300 350 567567 Index block1 IB 2 IB 3 275 Data block 5 Data block # Data block 6 Data block 7 201 202 250 251 252 275 300 data 300 350

6. UNIX file structure Data mode owner … Direct block 0 Direct block 1 … Single indirect Double indirect Triple indirect inode Data Index Data Index Data Index Data

7. UNIX or Win NT/XP mount / binusretcany Joe DJ abc / more cdexyz / binusretcany JoeDJ abc / more cdexyz mount DJF at any DJF onetwo