File systems

File system formats

FAT

Used in early versions of windows and DOS

Could handle up-to 2GB - 4GB

No security

FAT32

Used in windows 95, still used in some computers

Could handle up-to 32GB

No security

NTFS

Used in windows NT, Servers must use it

Could handle up-to 16EB

In folder security

Encryption

Compression

Disk quotas (restricts files usage, and space taken up on the disk)

Mounted Volumes

Files

What are files used for?

Files are used to store data on secondary storage

Give examples
  • Binary executable (programs)
  • Text files
  • Media files
What is the 8.3 file name format?

Used in windows NT

max 8char name

max 3char extension

What is the char limit now?

255char limit

List all file commands
  1. create
  1. delete
  1. open
  1. close
  1. read
  1. write
  1. append
  1. seek (goto)
  1. rename

What is sequential access

File is copied to main memory, sequentially and in order byte to byte, from the secondary storage.

Random access

Data can be read out of order.

What are the two operations

Read/Write

seek (basically a goto)

File allocation

Contiguous Allocation

Files are divided into blocks

Files are stored next to each other, and are not scattered

problem

What happens if we remove a file

We will have empty spaces, i assume this leads to defrag he never says but suggest it

solution

Allocation table

Allocation table

This is a table were when running a program, when you come to the end of a cluster, it tells you were the next cluster begins, in FAT

The FF FF represents the end of the program
Linked list allocation

FAT uses a table to point to the next block in the chain

This is fixed size

Hierarchical Directories

What is a Hierarchical Directory

This is where you have a root directory at the top

Below it there are folders which can contain both files and more folders

Image of Hierarchical Directories

Searching

Breadth first search

Will go down each layer, and check every node

Note: When i say each layer i mean, it will look at ever node on layer 1, then 2 and so on

it will switch folders when looking down each layer, it wont 'spike down each one'

Depth first search

If finds a directory, it will check the directory, until it has completed then it will go across or 'in breadth'