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BACS 371 Computer Forensics

BACS 371 Computer Forensics. File Systems within Partitions 1. Data Hierarchy. Computer Hard Disk Drive Partition ( file system ) File Physical File Logical File Cluster Sector Word Byte Bit. File Systems (See http://www.ntfs.com).

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BACS 371 Computer Forensics

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  1. BACS 371Computer Forensics File Systems within Partitions 1

  2. Data Hierarchy Computer Hard Disk Drive Partition (file system) File Physical File Logical File Cluster Sector Word Byte Bit

  3. File Systems(See http://www.ntfs.com) • A method for storing and organizing computer files and the data they contain to make it easy to find and access them • File System Types • FAT (File Allocation Table) • FAT12 • FAT16 • FAT32 • exFAT • NTFS (New Technology File System) • Functions • Manage “free space” • Allocate clusters to file • Track time (MAC – Modify, Access, Create)

  4. File System Comparisons

  5. Overall Performance Criteria NTFS5 NTFS FAT32 FAT16

  6. FAT File System This is all contained within a partition.

  7. A FAT file system is composed of four different sections. • The Boot Sector (aka Partition Boot Record, BIOS Parameter Block, Drive Parameter Block or Reserved Sector). This is always the first sector of the partition and includes some basic file system information (in particular, its type), pointers to the location of the other sections and the operating system's boot loader code. • The FAT Region. This contains two copies of the File Allocation Table for the sake of redundancy, although the extra copy is rarely used, even by disk repair utilities. These are maps of the partition, indicating how the clusters are allocated. • The Root Directory Region. This is a Directory Table that stores information about the files and directories in the root directory. With FAT32 it can be stored anywhere in the partition, however with earlier versions it is always located immediately after the FAT Region. • The Data Region. This is where the actual file and directory data is stored and takes up most of the partition. The size of files and subdirectories can be increased arbitrarily (as long as there are free clusters) by simply adding more links to the file's chain in the FAT. Note however, that each cluster can be taken only by one file, and so if a 1KB file resides in a 32KB cluster, 31KB are wasted.

  8. Sectors and Bytes per Cluster

  9. FAT Content • Database of • File names • Directory names • Date and time stamps (MAC) • Modify • Access • Create • Starting cluster number • Attributes • Archive • Hidden • System • Read Only • Located on outermost track of disk

  10. File Allocation Table • A partition is divided up into identically sized clusters, small blocks of contiguous space. Cluster sizes vary depending on the type of FAT file system being used and the size of the partition, typically cluster sizes lie somewhere between 2KB and 32KB. Each file may occupy one or more of these clusters depending on its size; thus, a file is represented by a chain of these clusters (referred to as a singly linked list). However these chains are not necessarily stored adjacently on the disk's surface but are often instead fragmented throughout the Data Region. • The File Allocation Table (FAT) is a list of entries that map to each cluster on the partition. Each entry records one of five things: • the address of the next cluster in a chain • a special end of file (EOF) character that indicates the end of a chain • a special character to mark a bad cluster • a special character to mark a reserved cluster • a zero to note that that cluster is unused

  11. File Allocation Table (FAT)

  12. FAT Entry Values Source: Wikipedia ? – 4 reserved bits, usually 0

  13. Directory table • A directory table is a special type of file that represents a directory (nowadays commonly known as a folder). Each file or directory stored within it is represented by a 32 byte entry in the table. Each entry records the name, extension, attributes (archive, directory, hidden, read-only, system and volume), the date and time of creation, the address of the first cluster of the file/directory's data and finally the size of the file/directory. • Aside from the Root Directory Table in FAT12 and FAT16 file systems which occupies the special Root Directory Region location, all Directory Tables are stored in the Data Region. • Legal characters for DOS file names include the following: • Upper case letters A-Z • Numbers 0-9 • Space (though trailing spaces are considered to be padding and not a part of the file name) •  ! # $ % & ( ) - @ ^ _ ` { } ~ ' • Values 128-255

  14. Root Directory

  15. Root Directory (& Subdirectories) Format

  16. File Attributes An attribute of 0x0F is used to designate a long file name entry

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