Evolution of Mac Filesystems

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Evolution of Mac Filesystems

• John Gillespie

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Brief Overview
HFS
LisaOS
MFS
HFS
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LisaOS

• Root level divided into different devices
• Tree

To reference a file, have to specify device name
and file name. -LISAHDD-FORMAT.TEXT
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LisaOS

• No directories, called a flat file system

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LisaOS Pages

• Page some chunk of a file
• Attributes
• Version
• Volume Id
• File Id
• Amt of data
• Position in file
• Forward link
• Backwards link

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LisaOS - Files

• Names
• Case sensitive
• Any ASCII, including non-printing
• 32 characters
• Space allocation
• File label
• LEOF vs PEOF

Example file
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LisaOS - Labels

• Early version of forks
• Application info for file

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LisaOS Important Structures

• Bitmap Allocation Table
• Catalog File

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LisaOS Redundancy

• Several copies of important structures
• File self-knowledge
• Scavenger
• Block sparing

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MFS

• Macintosh File System
• 1984
• Optimized for small, slow media

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MFS A Few Numbers
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MFS - Layout

• Flat file system
• Empty Folder
• Could have directories, emulated in finder
• Page allocation via linked list

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MFS Catalog File

• One file
• Directory handles
• Good
• Small file
• Bad
• Very slow

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MFS Notable Items
Resource Forks

• Data Forks
• Stores
• Icons
• Inserted Images
• Shapes
• Menus
• Important for GUI

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MFS Notable Items

• Metadata in resource forks holds information for
  the brand new Mac GUI!

Etc
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Hierarchical File System

• Introduced in 1985
• MFS too slow, too small

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HFS Catalog File

• Searching for directory names slow
• B-Tree
• 500,000 files lt19 node hops

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HFS Even Better Numbers
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HFS Forks 2

• N-forks

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HFS Cont.

• B-trees for allocation
• Unique Ids for Files

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HFS - Design

• First 2 Blocks Boot Blocks
• Master Directory Block
• Volume Bitmap
• Extent Overflow File
• Catalog File
• File Thread Record
• File Record
• Directory Thread Record
• Directory Record

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Hierarchical File System Plus!

• Introduced in 1998
• More Allocation Blocks
• Longer Filenames
• Larger Files

Thumbs Up To HFS
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HFS - Great Numbers
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HFS

• HFS Wrapper

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HFS Design

• HFS Boot Blocks
• Volume Header
• Allocation File
• Catalog File

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HFS - Volume Design Cont.

• Extents Overflow File
• Attributes File
• Startup File
• Alternate Volume Header

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HFS - Upgrades

• Journaling Features
• HFSX
• Inline Attribute Data Records
• Access Control List File Security

10.2.2 Jaguar
10.3 Panther
10.4 Tiger