There are three main ways to access files in a computer: sequential access, direct access, and index access. Sequential access reads files in order from beginning to end, direct access allows reading or writing any block directly by number, and index access uses pointers in an index to access records. A file system must be mounted before files can be accessed, with mount points typically being empty directories where the file system attaches within the overall file structure.

1. Access Methods
• Computer stores many files.
• Applications are used to access files.
• Three ways to access files:
- Sequential access method.
- Direct access method.
- Index access method.

2. Sequential Access Method:
• Serial Access.
• Information in the file is processed in order, one record after the
other.
• Operations:
- Read_next();
- Write_next();
- Rewind();
• For example, editors and compilers, audio or video cassette.

3. Direct Access Method:
• The file is viewed as a numbered sequence of blocks or records.
• Thus, we may read block 14, then read block 53, and then write block
7.
• Operations:
- Read(n);
- Write(n);
- Goto(n);
• E.g Database System.

4. Index Access Method:
• We first search the index and then use the pointer to access the file
directly and to find the desired record.
• The primary index file contains the contains the pointer to secondary
index file.
• Secondary index file contains the actual index of the block of the file.

5. File-System Mounting
• A file must be opened before it is used.
• File system must be mounted before it can be available to processes
on the system.
• Mount point—the location within the file structure where the file
system is to be attached.
• Typically, a mount point is an empty directory.

8. File-System Mounting
• For e.g external storage media (e.g CDROM and Floppy disk) are
usually mounted in subdirectory of the /mnt directory(i.e
/mnt/cdrom and /mnt/floppy).
• The mac OS X operating system searches for a file system on the
device. If it finds one, it automatically mounts the file system under
the /volumes directory, adding a folder icon labeled with the name of
the file system (as stored in the device directory).
• In some systems, like UNIX, the mount commands are explicit. A
system configuration file contains a list of devices and mount points
for automatic mounting at boot time, but other mounts may be
executed manually.