The document provides an outline on operating systems memory storage and management. It discusses how the OS must manage memory to ensure each process has enough space to execute without interfering with other processes. It describes different types of memory like cache, RAM, and disk and how the OS uses these properly. Specific topics covered include cache memory, RAM, virtual memory using swap files, the kernel, kernel types, shells, types of shells, shell scripting, and the four freedoms of open source software.

1. Operating
Systems
MIDTERM– LESSON OUTLINE

2. OS - Memory Storage and
Management

3. OS - Memory Storage and
Management
• Besides managing hardware
and software resources on the
system, the OS must manage
resources and memory.
• Each process must have
enough memory in which to
execute, and It can neither run
into the memory space of
another process, Nor be run
into by another process.

4. OS - Memory Storage and
Management
• The different types of memory in the system must be
used properly so that each process can run most
effectively.
o Cache
o Ram
o Disk

5. Cache Memory
• A section of a computer's memory which temporarily
retains recently accessed data in order to speed up
repeated access to the same data.
• It provides rapid access without having to wait for
systems to load.
• Very Costly

6. RAM
• Random access memory
(RAM) is the best known
form of computer memory.
• RAM is considered "random
access" because you can
access any memory cell
directly if you know the row
and column that intersect at
that cell.

7. RAM
• The more RAM your computer has, the faster
programs can function.
• Remember, that if the power is turned off, then all
data left in RAM, that has not been saved to the hard
drive, is lost.

8. Virtual Memory
• Virtual Memory – a method of
using hard disk space to
provide extra memory. It
simulates additional RAM.
• In Windows, the amount of
virtual memory available,
equals the amount of free
RAM plus the amount of disk
space allocated to the swap
file.

9. Virtual Memory – Swap
File
• A swap file is an area of your hard disk that is set aside for virtual
memory. Swap files can be either temporary or permanent.

10. Kernel

11. Kernel
• Core or nucleus of an operating system
• Interacts with the hardware
• First program to get loaded when the system starts and
runs till the session gets terminated
• Different from BIOS which is hardware dependent.
• Kernel is software dependent

12. Kernel

13. Kernel types
• Monolithic
o All OS related code are stuffed in a single module
o Available as a single file
o Advantage : Faster functioning
• Micro
o OS components are isolated and run in their own
address space
o Device drivers, programs and system services run
outside kernel memory space
o Supports modularity
o Lesser in size

14. Shell
• Program that interacts with kernel
• Bridge between kernel and the user
• Command interpreter
• User can type command and the command is conveyed
to the kernel and it will be executed

15. Types of Shell
• Sh – simple shell
• BASH – Bourne Again Shell
• KSH – Korne Shell
• CSH – C Shell
• SSH – Secure Shell
• To use a particular shell type the shell name at the command
prompt.
o Eg $csh – will switch the current shell to c shell
• To view the available shells in the system, type cat /etc/shells at the
command prompt
• To view the current shell that is being used, type echo $SHELL at
the command prompt

16. Operating System
User 1
User 2

17. Shell Scripting
• Shell scripting is the most useful and powerful feature in
Linux
o Minimizes typing of repetitive command
o Can schedule jobs to run in the system
o Can initiate back up activities for system administration
o Similar to batch files in DOS, but more powerful than Batch files

18. Working with shell script
• Open a file with extension .sh using vi editor
• We can type any number of commands that we use to
type at command prompt
• Save the file
• Execute the file
o sh file.sh
o ./file.sh (if the file has execution permission)

19. 4 Freedoms with FOSS
• Freedom to run the software anywhere
• Freedom to study how the programs work. i.e source
code will be accessible
• Freedom to redistribute copies
• Freedom to improve the software
• If a software has all these 4 freedoms, then it is a FOSS

20. Copyleft
• Termed by Richard Mathew Stallman
• Copyleft statement:
o “Copying and redistribution are permitted in any medium provided this notice is
preserved.”

21. Linux
• Developed in 1991 by Linus Torvalds
• Used in most of the computers, ranging from
super computers to embedded system
• Multi user
• Multi tasking
• Time sharing
• Monolithic kernel

22. Free Software Foundation
• Founded by Richard Stallman in 1983
• Organisation that started developing copylefted
programs
• Project – GNU Project
o GNU Not Unix
o Recursive expansion

23. Components

24. Interrupts
• Interrupt transfers control to the interrupt service routine
generally, through the interrupt vector, which contains
the addresses of all the service routines.
• Interrupt architecture must save the address of the
interrupted instruction.
• Incoming interrupts are disabled while another interrupt
is being processed to prevent a lost interrupt.
• A trap is a software-generated interrupt caused either by
an error or a user request.
• An operating system is interrupt driven.

25. Modes
• Superviser Mode
o Unrestricted access to hardware
• Protected Mode
o Everything Else

26. Process

27. 27
PROCESSESPROCESS CONCEPT:
A program is passive; a process active.
Attributes held by a process include
•hardware state,
•memory,
•CPU,
•progress (executing)
WHY HAVE PROCESSES?
Resource sharing ( logical (files) and physical(hardware) ).
Computation speedup - taking advantage of multiprogramming – i.e. example of a
customer/server database system.

28. 28
PROCESSES PROCESS STATE
 New The process is just being put together.
 Running Instructions being executed. This running process holds the CPU.
 Waiting For an event (hardware, human, or another process.)
 Ready The process has all needed resources - waiting for CPU only.
 Suspended Another process has explicitly told this process to sleep. It will be
awakened when a process explicitly awakens it.
 Terminated The process is being torn apart.

29. 29
PROCESS CONTROL BLOCK:
CONTAINS INFORMATION ASSOCIATED WITH EACH
PROCESS:
It's a data structure holding:
 PC, CPU registers,
 memory management information,
 accounting ( time used, ID, ... )
 I/O status ( such as file resources ),
 scheduling data ( relative priority, etc. )
 Process State (so running, suspended, etc. is simply
a field in the PCB ).
PROCESSES Process State

30. 30
The act of Scheduling a process means changing the active PCB pointed to by the CPU.
Also called a context switch.
A context switch is essentially the same as a process switch - it means that the memory,
as seen by one process is changed to the memory seen by another process.
See Figure on Next Page
SCHEDULING QUEUES:
(Process is driven by events that are triggered by needs and availability )
Ready queue = contains those processes that are ready to run.
I/O queue (waiting state ) = holds those processes waiting for I/O service.
PROCESSES
Scheduling
Components

31. 3:
Proces
ses
31
PROCESSES
Scheduling
Components
The CPU switching
from one process to
another.

32. Process Scheduling
• First Come – First Serve
o Long process may make others starve
• Shortest Job First
o Long process may starve
• Round Robin
o Lots of time used in switching
• Priority Scheduling
o Low priority Job Starve

33. Threads

34. Thread
• A thread of execution is the smallest sequence of
programmed instructions that can be managed
independently by an operating system schedule
• Processes are typically independent, while threads exist
as subsets of a process

35. Multitasking and
Multithreading
• Multitasking refers to a computer's ability to perform
multiple jobs concurrently
o more than one program are running concurrently, e.g.,
UNIX
• A thread is a single sequence of execution within a
program
• Multithreading refers to multiple threads of control
within a single program
o each program can run multiple threads of control within it,
e.g., Web Browser

36. Threads and ProcessesCPU
Process 1 Process 3Process 2 Process 4
main
run
GC

37. What are Threads Good
For?
• To maintain responsiveness of an application during a
long running task.
• To separate independent tasks and make the execution
faster.
o If a thread waits for I/O, other thread can execute in meanwhile

38. Cloud Computing

39. Cloud Computing
• A type of outsourcing of computer services
• Similar to the way in which the supply of electricity is
outsourced. Users can simply use it.
• They do not need to worry where the electricity is from,
how it is made, or transported. Every month, they pay for
what they consumed.
• Idea behind cloud is similar

40. Cloud Computing
• The user can simply use storage, computing power, or
specially crafted development environments, without
having to worry how these work internally.
• Cloud computing is a systems architecture model for
Internet-based computing.
• It is the development and use of computer technology on
the Internet

41. • Connects to the cloud via the Internet
o Does computing tasks, or
o Runs applications, or
o Stores Data
The Average Cloud user

42. Do you Use the Cloud?

43. • An Internet connection
• An account - Created with a user name and a password
• Agree to Terms
The Cloud Requires

44. So what is the cloud?
Computing and software resources that are delivered on demand, as service.
(2013, January) A Walk in the Clouds. Cloud Computing, CDW-G Reference Guide., 3-5.

45. Cloud Computing – Simple Definition
Cloud Computing = Software as a Service
+ Platform as a Service
+ Infrastructure as a Service
+ Data as a Service

46. Cloud Computing – Simple Definition
Cloud Computing = Software as a Service
+ Platform as a Service
+ Infrastructure as a Service
+ Data as a Service
• Software as a Service (SaaS)
̵ From end user’s point of view
̵ Apps are located in the cloud
̵ Software experiences are delivered through the Internet
̵ Example: Google Docs

47. Cloud Computing – Simple Definition
Cloud Computing = Software as a Service
+ Platform as a Service
+ Infrastructure as a Service
+ Data as a Service
• Platform as a Service (PaaS)
̵ From developer’s point of view (i.e. cloud users)
̵ Cloud providers offer an Internet-based platform to
developers who want to create services but don't want to
build their own cloud
̵ Example: Web Hosting

48. Cloud Computing – Simple Definition
Cloud Computing = Software as a Service
+ Platform as a Service
+ Infrastructure as a Service
+ Data as a Service
• Infrastructure as a Service (IaaS)
̵ Cloud providers build datacenters
• Power, scale, hardware, networking, storage, distributed systems, etc
̵ Datacenter as a service
̵ Cloud users rent storage, computation, and maintenance from
cloud providers (pay-as-you-go; like utility)

49. • Computers have internal or hard drive storage(C: Drive)
• CPU has a drive for storing programs, documents,
pictures, videos, presentations, etc…
Computer Storage
Standard Computer Tower
or Central Processing Unit
(CPU)
Inside the Computer

50. External Storage
External Hard DriveCD/DVD Thumb Drive
SD Card Micro SD Card
 Allows your content to become mobile
 Save to the storage device
 Take device to any compatible computer
 Open and use content

51. • Multiple work stations talk to one unit that stores
information and data.
• Data is not saved to the C: drive, but to a network drive
• Can retrieve the data stored to the network from any of
the connected workstations.
Networked Storage

52. • Create an Account – User
name and password
• Content lives with the
account in the cloud
• Log onto any computer
with Wi-Fi to find your
content
Cloud Storage

53. Software and
applications
More than
Storage

54. • Google Docs
• SkyDrive
• Box
Document Creation

55. Advantages of Cloud Computing
• Lower computer costs:
o You do not need a high-powered and high-priced computer
to run cloud computing's web-based applications.
o Since applications run in the cloud, not on the desktop PC,
your desktop PC does not need the processing power or
hard disk space demanded by traditional desktop software.
o When you are using web-based applications, your PC can be
less expensive, with a smaller hard disk, less memory, more
efficient processor...
o In fact, your PC in this scenario does not even need a CD or
DVD drive, as no software programs have to be loaded and
no document files need to be saved.
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56. Advantages of Cloud Computing
• Improved performance:
o With few large programs hogging your computer's
memory, you will see better performance from your PC.
o Computers in a cloud computing system boot and run
faster because they have fewer programs and processes
loaded into memory…
• Reduced software costs:
o Instead of purchasing expensive software applications,
you can get most of what you need for free-ish!
• most cloud computing applications today, such as the Google Docs
suite.
o better than paying for similar commercial software
• which alone may be justification for switching to cloud applications.
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57. Advantages of Cloud Computing
• Instant software updates:
o Another advantage to cloud computing is that you are no longer
faced with choosing between obsolete software and high upgrade
costs.
o When the application is web-based, updates happen automatically
• available the next time you log into the cloud.
o When you access a web-based application, you get the latest
version
• without needing to pay for or download an upgrade.
• Improved document format compatibility.
o You do not have to worry about the documents you create on your
machine being compatible with other users' applications or OSes
o There are potentially no format incompatibilities when everyone is
sharing documents and applications in the cloud.
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58. Advantages of Cloud Computing
• Unlimited storage capacity:
o Cloud computing offers virtually limitless storage.
o Your computer's current 1 Tbyte hard drive is small
compared to the hundreds of Pbytes available in the cloud.
• Increased data reliability:
o Unlike desktop computing, in which if a hard disk crashes
and destroy all your valuable data, a computer crashing in
the cloud should not affect the storage of your data.
• if your personal computer crashes, all your data is still out there
in the cloud, still accessible
o In a world where few individual desktop PC users back up
their data on a regular basis, cloud computing is a data-
safe computing platform!
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59. Advantages of Cloud Computing
• Universal document access:
o That is not a problem with cloud computing, because you
do not take your documents with you.
o Instead, they stay in the cloud, and you can access them
whenever you have a computer and an Internet connection
o Documents are instantly available from wherever you are
• Latest version availability:
o When you edit a document at home, that edited version is
what you see when you access the document at work.
o The cloud always hosts the latest version of your
documents
• as long as you are connected, you are not in danger of having an
outdated version
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60. Advantages of Cloud Computing
• Easier group collaboration:
o Sharing documents leads directly to better collaboration.
o Many users do this as it is an important advantages of cloud
computing
• multiple users can collaborate easily on documents and projects
• Device independence.
o You are no longer tethered to a single computer or network.
o Changes to computers, applications and documents follow
you through the cloud.
o Move to a portable device, and your applications and
documents are still available.
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61. Disadvantages of Cloud Computing
• Requires a constant Internet connection:
o Cloud computing is impossible if you cannot connect
to the Internet.
o Since you use the Internet to connect to both your
applications and documents, if you do not have an
Internet connection you cannot access anything, even
your own documents.
o A dead Internet connection means no work and in
areas where Internet connections are few or
inherently unreliable, this could be a deal-breaker.
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62. Disadvantages of Cloud Computing
• Does not work well with low-speed connections:
o Similarly, a low-speed Internet connection, such as that
found with dial-up services, makes cloud computing painful
at best and often impossible.
o Web-based applications require a lot of bandwidth to
download, as do large documents.
• Features might be limited:
o This situation is bound to change, but today many web-
based applications simply are not as full-featured as their
desktop-based applications.
• For example, you can do a lot more with Microsoft PowerPoint
than with Google Presentation's web-based offering
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63. Disadvantages of Cloud Computing
• Can be slow:
o Even with a fast connection, web-based applications
can sometimes be slower than accessing a similar
software program on your desktop PC.
o Everything about the program, from the interface to
the current document, has to be sent back and forth
from your computer to the computers in the cloud.
o If the cloud servers happen to be backed up at that
moment, or if the Internet is having a slow day, you
would not get the instantaneous access you might
expect from desktop applications.
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64. Disadvantages of Cloud Computing
• Stored data might not be secure:
o With cloud computing, all your data is stored on the
cloud.
• The questions is How secure is the cloud?
o Can unauthorised users gain access to your confidential
data?
• Stored data can be lost:
o Theoretically, data stored in the cloud is safe, replicated
across multiple machines.
o But on the off chance that your data goes missing, you
have no physical or local backup.
• Put simply, relying on the cloud puts you at risk if the cloud lets
you down.
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65. Questions?