The document discusses the key functions of an operating system including process management, memory management, file management, device management, security management, and user interface. It provides details on how the OS manages files, interacts with users through command line and graphical interfaces, provides security, manages devices by using drivers, and allocates CPU time and memory to running processes. Memory management techniques like paging and virtual memory allow processes to be stored non-contiguously in memory across physical and secondary storage. Process scheduling aims to allocate CPU time fairly among processes.

1. FUNCTIONS OF OS
MODULE 1

2. FUNCTIONS OF OS
 Process management
 Memory management
 File management
 Device management
 Security management
 User interface

3. FILE MANAGEMENT
 Provides a hierarchical structure for
the entire data.
 Provides a set of commands to
perform various operations on the
file.
 The file manager
 Controls access to files.
 Supervises the creation, deletion, and
modification of files.
 Controls the naming of files.
 Supervises the storage of files.
 Responsible for archiving and
backups.

4. USER INTERFACE
 Provides 2 types of user interface
 CLI
 Provides an interactive terminal.
 User can communicate with the
system through the terminal.
 Commands are used to initiate a
program.
 GUI
 Provides users with pictures,
icons, buttons and dialog boxes.
 User sends instructions by moving
a pointer on the screen.

5. SECURITY MANAGEMENT
 Provides internal security to the
system .
 Can be provided by using
 User Authentication
 Back up of data

6. DEVICE MANAGEMENT
 Managing the various devices
connected to the system.
 OS communicates with the
hardware by using the
software called device driver.
 Spooling
 Refers to storing jobs in a
buffer, where a device can
access them when it is
ready.
 Provides a waiting station
for devices.
 Eg: Print spooling.

7. PROCESS MANAGEMENT
 Manages all processes that are running on a
computer.
 It is responsible for
 Process creation and deletion.
 Process suspension and resumption.
 Process scheduling
 Resource allocation

8. PROCESS STATE
 New
 The process is being created.
 Ready
 The process is waiting to be assigned
to a process.
 Running
 Instructions are being executed.
 Waiting
 The process is waiting for some
event to occur.
 Terminated
 The process has finished execution.

9. PROCESS CONTROL BLOCK (PCB)
 A data structure maintained by
the OS for each process
 It contains
 Process ID
 Process state
 Program counter
 CPU scheduling information
 I/O status information

10. CPU SCHEDULING
 Process of allocating CPU time among all processes.
 Scheduling can be performed with the help of
schedulers.
 For scheduling purposes, different queues are used.
 Job queue
 Set of all jobs in the system.
 Ready queue
 Set of all processes waiting for the CPU.
 Device queue
 Set of processes waiting for an I/O device.

11. CPU SCHEDULING QUEUES

12. CPU SCHEDULERS
 Long-term scheduler (job scheduler)
 Selects job from the job queue and loads it into the main
memory for execution.
 Short-term scheduler (CPU scheduler)
 Selects a process from the ready queue and allocates CPU to
it.
 Medium term scheduler
 Decides whether to introduce a process from running state
to a waiting state or a waiting state to the ready state.

13. CPU SCHEDULING
 CPU scheduling decisions may take place when a
process:
1. Switches from running to waiting state
2. Switches from running to ready state
3. Switches from waiting to ready
4. Terminates
 Conditions 1 & 4 comes under non-preemptive
scheduling.
 All other conditions come under preemptive
scheduling.

14. CPU SCHEDULING
 Non-preemptive scheduling
 Once the CPU has been allocated to a process, the
process keep the CPU until it release the CPU either by
terminating or by switching to waiting state.
 Preemptive scheduling
 Scheduler can remove a process from the running state
to the other state in order to allow other processes to
run.

15. PROCEDURES FOR CPU SCHEDULING
 First Come First Served (FCFS)
 Round Robin Scheduling

16. First Come First Served (FCFS)
 All processes are enter in a queue.
 New process arrived is placed at the end of the queue.
 Process at the start of the queue is dispatched to the
processor.
 Falls under non-preemptive scheduling.
 If a process takes a very long time to complete, then other
processes have to wait .

17. Round Robin Scheduling
 Processes are allocated CPU time on a turn basis.
 Each process is allocated a fixed time to use the CPU.
 The time is known as time slice or quantum period.
 Falls under preemptive scheduling.

18. DEADLOCK

19. DEADLOCK
 A set of blocked processes each
holding a resource and waiting to
acquire a resource held by another
process in the set.

20. DEADLOCK
 Various conditions are
o Mutual exclusion
 Only one process at a time can use a resource.
 Hold and wait
 A process holding at least one resource is waiting to acquire
additional resources held by other processes.
 No preemption
 A resource can be released only after that process has
completed its task.
 Circular wait
 There must be a circular chain of 2 or more processes where
each is waiting for a resource held by the next member of the
chain.

21. MEMORY MANAGEMENT
 The part of the OS that performs memory management is
known as Memory Manager.
 Memory Manager is responsible
 Keeping track of which parts of memory are currently
being used and by whom.
 Decide which processes are to be loaded into memory
when memory space becomes available.
 Allocate and de-allocate memory space as needed

22. MEMORY MANAGER
 The main task of Memory Manager is
 Memory Relocation
 Memory Protection and Sharing

23. MEMORY RELOCATION
 Swapping
 Moving a process temporarily out of memory to a backing
store and then brought back to memory for continued
execution.

24. MEMORY ALLOCATION
 OS allocates a portion of the primary memory to each
process for its own use.
 Methods used for memory allocation
 First Fit
 Allocate the first hole that is big enough.
 Best Fit
 Allocate the smallest hole that is big enough.
 Worse Fit
 Allocate the largest hole.

25. MEMORY ALLOCATION
Fragmentation
Process of splitting the primary
memory into segments as the
memory is allocated and de-
allocated.

26. PAGING
 A memory management scheme that allows processes
to be stored non-contiguously in memory.
 Physical memory is divided into fixed sized blocks
called page frames.
 Logical memory is divided into fixed sized blocks
called pages.
 When a program is loaded into memory, each page is
loaded into a page frame and the frame can be residing
anywhere in the memory.
 OS maintains a page table for keeping track of the
pages of the process.

27. PAGING
 Logical address is divided into 2 parts
 Page number (p)
 Page Offset (d)
 To map the logical address to physical address in memory a
mapping table called page table is used.
 To map a given logical address to a physical address, Os
first extracts the page no and offset.
 If the page no is valid, the system uses page no to find the
corresponding page frame no in the page table.
 The page frame no is attached to the page offset to form
the physical address in memory

28. PAGING
CPU p d
page table
f
f d
physical
memory
Page No

29. VIRTUAL MEMORY
 A memory larger than the physical memory placed on
the hard disk.
 Data is stored on the VM and can be loaded into main
memory whenever needed.
 The process of swapping pages from VM to main
memory is known as page –in or swap-in.
 In VM systems, the page table of each process stores
an additional bit to identify the location of the page.
 If the bit is 1, the page is in the main memory
otherwise in the virtual memory.

30. VIRTUAL MEMORY
 Wherever a page reference is made, the Os checks the
page table for that page.
 If the page is not in the main memory, a page fault
occurs and control is passed to the page fault routine
in the Os.
 Page fault routine checks whether the virtual address
of that page is valid or not.
 If it is valid, locates the free frame in the memory and
allocate the process.
 If it is not valid, it terminates the process.

31. EMBEDDED SOFTWARE
 A software written to control machines or devices.