Macintosh Hierarchical File System by Imad Qamar 2190-B

What is HFS? Hierarchical File System (HFS), is a file system developed by Apple Computers for use on computers running Mac OS. Hierarchical File System (HFS), is a file system developed by Apple Computers for use on computers running Mac OS. Designed for use on floppy and hard disks. Designed for use on floppy and hard disks. Also known as Mac OS Standard. Also known as Mac OS Standard.

Design The Hierarchical File System divides a volume into logical blocks. The Hierarchical File System divides a volume into logical blocks. Logical blocks are then grouped together into allocation blocks. Logical blocks are then grouped together into allocation blocks. Size of allocation block depends upon size of volume. Size of allocation block depends upon size of volume. No# of allocation blocks: 65,536 No# of allocation blocks: 65,536

HFS Volume Five structures make up an HFS volume. Five structures make up an HFS volume. Boot Blocks Boot Blocks Master Directory Block Master Directory Block Volume Bitmap Volume Bitmap Extent Overflow File Extent Overflow File Catalog File Catalog File

Boot Blocks Logical blocks 0 and 1. Logical blocks 0 and 1. Contain system startup information. Contain system startup information. e.g. System and Shell (Finder) Files loaded at startup. e.g. System and Shell (Finder) Files loaded at startup.

Master Directory Block Logical Block 2 Logical Block 2 Defines a variety of data about the volume: Defines a variety of data about the volume: Time of volume creation. Time of volume creation. Size of logical structures (e.g. allocation blocks) Size of logical structures (e.g. allocation blocks) Location of volume structures. Location of volume structures.

Volume Bitmap Logical Block 3. Logical Block 3. Keeps track of which allocation blocks are in use and which are free. Keeps track of which allocation blocks are in use and which are free. Allocation represented by a bit: Allocation represented by a bit: Set = Block in use. Set = Block in use. Not set = Block is free. Not set = Block is free.

Extent Overflow File Follows a B-tree data structure. Follows a B-tree data structure. Contains extra extents to record which allocation blocks are allocated to which files. Contains extra extents to record which allocation blocks are allocated to which files. Is used after all 3 extents of the Catalog File are used up. Is used after all 3 extents of the Catalog File are used up.

Catalog File Also follows a B-tree data structure. Also follows a B-tree data structure. Contains records for all the files/directories stored in the volume. Contains records for all the files/directories stored in the volume. File/Directories are located by their Catalog Node ID. File/Directories are located by their Catalog Node ID.

Catalog File (Continued) Each file consists of: Each file consists of: File Thread Record File Thread Record File Record File Record Each directory consists of: Each directory consists of: Directory Thread Record Directory Thread Record Directory Record Directory Record

Catalog File (Continued) File Thread Record: Stores: File Thread Record: Stores: Filename Filename CNID of its parent directory. CNID of its parent directory. File Record: Stores meta data of a file: File Record: Stores meta data of a file: CNID CNID Size of file Size of file

Catalog File (Continued) Directory Thread Record: Stores: Directory Thread Record: Stores: Directory name. Directory name. CNID of its parent directory. CNID of its parent directory. Directory Record: Stores data such as: Directory Record: Stores data such as: No# of files stored in directory No# of files stored in directory CNID of the directory CNID of the directory

HFS (Some more info) Max file size:2 GB Max no# of files:65535 Max filename size:31 char Max Volume size:2 TB Directory Contents:B-tree File Allocation:B-tree Bad Blocks:B-tree

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