Unix by Nick Gomez, Chris Rees, Brian Hernandez, Hector Rodriguez

Implementation Of File System

• Directories contain file names and pointers
• Pointer is called an i-number (index number) of the file
• I-number references the information of the file in the system table

File Information

• Owner name
• Protection bits
• Physical address of location on disk
• Size
• Time of modification
• Number of links to file
• Directory bit
• Special file bit
• “Large” or “small” bit

Efficiency of File System

• File system provides satisfactory performance
• 7621 line test program
• Total time of 35.9 seconds, 212 lines per second
• Time taken for each element:

63.5% Assembler execution

20.0% Disk wait time

16.6% System overhead

I/O Calls

• Eliminate differences between different devices
• open(name, flag) and Create
• No user-visible automatic locks on files, unnecessary and insufficient
• Sufficient internal interlocks
• Files are sequential
• read(filep, buffer, count), write(filep, buffer, count)
• seek(filep, base, offset)