QMCS 360 Class Notes

	QMCS 360 Class Notes # 19	Dr. Rick Smith Quantitative Methods and Computer Science
Dr. Smith Home \| Research \| Classes \| Blackboard \| Cryptosmith \| QMCS Home \| UST A-Z \| UST Home last update: Tuesday, November 22, 2005

Scheduling software

Deadline for spring CIG grants - Tue, Nov 29

Outline

CP/M File System

File system for 8-bit computers

Based on DEC OSes, especially RT-11 (device letters)
Heavily influenced MS-DOS
Never made the jump to 16-bits

Flat file system - no hierarchy
Directory entry format

User ID (1 byte)
File name (8 bytes)
File type/extension (3 bytes)
Extent # (1 byte) - which part of the file this describes (incremental)
Block pointers used (1 byte)
List of 16 block pointers (2 bytes each)

Internal fragmentation problem - no end of data marker

FAT File System

Classic MSDOS file structure, has tried to evolve to keep up with disk sizes
FAT = File Access Table

Centerpiece of the disk structure
All data accessed in chunks of blocks/sectors called "Clusters"
Files consist of sets of clusters linked together in order
Links appear in the FAT - one entry per cluster
If the link = 0, the cluster is free to allocate
Usually have 2 or more copies of FAT for reliability/recovery

Different FATs:

FAT12 = 12-bit cluster addresses
FAT16 = 16-bit
FAT32 = guess

Elements of the disk layout in FAT

Reserved sectors (boot data, configuration data)
FAT #1
FAT #2 (backup of #1)
Root Directory (Cluster #1)
rest of disk consists of Clusters #2 through N)

FAT directory entry contents

File name (8 bytes) - first byte flags free or 'special' (LFN)
Extension (3 bytes)
Attributes (1 byte)
Time/Date (2 bytes each)
First block number (2-4 bytes, depending on 12/16/34)

Long file names (LFN)

Special format entries in the directory

NTFS

Introduced for Windows NT

File system for "real players"
Implements state of the art features: User IDs, access control lists, huge devices, etc
"Everything is in a file" unlike FAT
Uses clusters, like FAT

Hierarchical
Inheritance of ownership permissions

QMCS 360

Class Notes # 19

Dr. Rick Smith Quantitative Methods and Computer Science

Scheduling software

Deadline for spring CIG grants - Tue, Nov 29

Outline

CP/M File System

File system for 8-bit computers

Based on DEC OSes, especially RT-11 (device letters) Heavily influenced MS-DOS Never made the jump to 16-bits

Flat file system - no hierarchy Directory entry format

User ID (1 byte) File name (8 bytes) File type/extension (3 bytes) Extent # (1 byte) - which part of the file this describes (incremental) Block pointers used (1 byte) List of 16 block pointers (2 bytes each)

Internal fragmentation problem - no end of data marker

FAT File System

Classic MSDOS file structure, has tried to evolve to keep up with disk sizes FAT = File Access Table

Different FATs:

FAT12 = 12-bit cluster addresses FAT16 = 16-bit FAT32 = guess

Elements of the disk layout in FAT

Reserved sectors (boot data, configuration data) FAT #1 FAT #2 (backup of #1) Root Directory (Cluster #1) rest of disk consists of Clusters #2 through N)

FAT directory entry contents

File name (8 bytes) - first byte flags free or 'special' (LFN) Extension (3 bytes) Attributes (1 byte) Time/Date (2 bytes each) First block number (2-4 bytes, depending on 12/16/34)

Long file names (LFN)

Special format entries in the directory

NTFS

Introduced for Windows NT

File system for "real players" Implements state of the art features: User IDs, access control lists, huge devices, etc "Everything is in a file" unlike FAT Uses clusters, like FAT

Hierarchical Inheritance of ownership permissions

Dr. Rick Smith

Quantitative Methods
and
Computer Science

Based on DEC OSes, especially RT-11 (device letters)
Heavily influenced MS-DOS
Never made the jump to 16-bits

Flat file system - no hierarchy
Directory entry format

User ID (1 byte)
File name (8 bytes)
File type/extension (3 bytes)
Extent # (1 byte) - which part of the file this describes (incremental)
Block pointers used (1 byte)
List of 16 block pointers (2 bytes each)

Classic MSDOS file structure, has tried to evolve to keep up with disk sizes
FAT = File Access Table

FAT12 = 12-bit cluster addresses
FAT16 = 16-bit
FAT32 = guess

Reserved sectors (boot data, configuration data)
FAT #1
FAT #2 (backup of #1)
Root Directory (Cluster #1)
rest of disk consists of Clusters #2 through N)

File name (8 bytes) - first byte flags free or 'special' (LFN)
Extension (3 bytes)
Attributes (1 byte)
Time/Date (2 bytes each)
First block number (2-4 bytes, depending on 12/16/34)

File system for "real players"
Implements state of the art features: User IDs, access control lists, huge devices, etc
"Everything is in a file" unlike FAT
Uses clusters, like FAT

Hierarchical
Inheritance of ownership permissions