Q1. Definitions

• Platter
• Track
• Cylinder
• Sector
• Block

Block vs Cluster

• What ext2 calls blocks, FAT calls clusters; the concept is the same.
• Make sure you identify the correct term.

512GiB disk drive with 1024 byte sectors

4096 byte blocks

8192 byte blocks

16384 byte blocks

Large block size

• OS has fewer blocks to manage.
• Less metadata overhead for the entire disk.

Small block size

• Reduced internal fragmentation.

Q2. Access Time

Q3. What happens when the code is executed

#include <stdio.h>

int main()
{
    FILE *fp = fopen(“hello.txt”, “w”);
    fprintf(fp, “Hello world!\n”);
    fclose(fp);
}

• fopen
• write content
• close file

• fopen creates a new entry in the per-user OFT

• Allocates read/write buffer with the entry.

• Calls low-level open operation.

• fopen
  • OS creates file
  • OS opens file
• write content
• close file

• OS searches in the file list of the current directory for "hello.txt".
• Doesn't exist. Check to see that correct permission is set to create files.
• Checks the disk bitmap for available blocks and allocate the blocks for the new file.
• Allocate an inode and populate the content.
• Add the inode number into the directory with the name "hello.txt".

• fopen
  • OS creates file
  • OS opens file
• write content
• close file

• Creates a new entry in the system-wide OFT (unless the file is already open).
• The private OFT now points to this entry in the system OFT.
• fopen returns to the caller a pointer fp to the private OFT entry, which is stored in the FILE structure.

• fopen
  • OS creates file
  • OS opens file
• write content
• close file

• The fprintf writes "Hello world!\n" into the file's buffer.
  • The buffer will be "flushed" when
    • buffer is full
    • program exits
    • stream is closed
    • on a newline only if it is line buffered
    • explicitly called
• In this case, it is not immediately flushed.

• fopen
  • OS creates file
  • OS opens file
• write content
• close file

• Flush the buffer
• OS checks inode to figure out where on the disk should the data be stored.
• Block address is translated into its physical location (platter, surface, cylinder, sector)
• Send command to the drive controller to transfer the data to that location.
• Entries in the OFT are removed.

• fopen
  • OS creates file
  • OS opens file
• write content
• close file