Chapter 1-2 _ Operating Systems.pdf

Operating System Software
● Operating System (OS) – Software that controls the
overall operation of a computer

What is an operating system (OS)?
Operating System Software
Software which manages the overall operation of the computer system
including:
● hardware (CPU, RAM, I/O)
● security
● system interface
● application interface

What is an operating system (OS)?

What “is” an operating system?
Software files
(programs) which are
stored on the hard
disk
● kernel with the
internal programs
● external programs
Supporting Data Files

The kernel
The operating system software file (program) which is copied into
RAM, usually from the hard disk drive, during the boot-up.
The kernel remains in RAM while the computer is on and is in
charge of the overall operation of the computer system.
The kernel contains the “internal programs” for the most often
used operations like copying files.
● kmem (Linux)
● command.exe (Microsoft)

Kernel
● Kernel – The internal part of the operating system.
● Those software components that perform the basic functions
required by the computer.
● File management
● Memory management (RAM)
● Security

The functions of an operating
system
1. Manages and Interacts with Computer
Hardware
2. Provides and Manages System Security
3. Provides the System Interface
4. Provides the Interface for Application
Software

1. Manages and Interacts with Computer Hardware
● Manages the CPU
- What software programs
the
CPU works on and when
● Manages RAM
- What is stored in RAM and
where it is stored
- Virtual memory
- OS will send message
when RAM is full

(continued)
● Provides the interface for
storage devices and manages
how data is stored on those
devices
- in charge of formatting disks
- creates sectors and clusters
- creates F.A.T. or V.T.O.C.
- sends message when disk is
full or there is some other
problem with writing data to
the disk
- virtual memory
- CD-ROM, DVD-ROM
- Flash drive

(continued)
● Provides the Interface for Input
and Output Devices
● keyboard, mouse, printer,
● device drivers = software
programs which allow the
hardware device to be used
by the operating system and
by application software

Preemptive Multitasking vs Cooperative Multitasking
Cooperative Multitasking
OS gives CPU processing
time to other programs at a
logical point, usually during
idle time
Preemptive Multitasking
OS allocates CPU time
between the different
programs based on amount
of time and priority of the
software application

Multiprocessing with Multiple CPU’s
● Asymmetric Multiprocessing = Tasks are assigned to a specific
CPU and each CPU has its own RAM memory
● Symmetric Multiprocessing = Tasks are assigned to any available
CPU and CPU’s can share RAM memory

Processes
● Scheduler – Maintains a record
of the processes.
● Adds new processes when
launched.
● Removes old processes
when completed.
● Uses a process table.
● Process Table – Information
about each process including:
● Main memory cells (RAM)
● Priority
● Running or waiting (input
from user or saving to disk)

● Viewing processes with Microsoft Windows
● Task Bar – Right-click, Task Manager
● Ending a process – Killing the process

Processes
● Dispatcher -
Oversees the
execution of each
process by the CPU.
● Gives each process a
time slice of CPU time.
● Changes between
processes.

Server (Multiuser) Operating
Systems
● Found on mainframes, minicomputers and PCs
● server = a computer which processes information (CPU and RAM) ,
stores information (hard disk), and/or provides access to peripheral
devices (printers) for multiple users
● Email
● Web
● Gaming

Examples of Server Operating
Systems
● MAC OS X Server
● Windows Server

Advantages/Disadvantages of Server Operating
Systems
Advantages
● Central location for the
installation and administration
of all software and data
● More cost effective - less
expensive than multiple
computers (PCs, Macs)
Disadvantages
● Single source for possible
problems
● Loss of individual user control
of their own software, data,
and peripherals

Virtual Memory
Virtual Memory (VM) = the ability of the CPU and the operating system
software to use the hard disk drive as additional RAM when needed
(safety net)
Good – no longer get “insufficient memory” error
Bad - performance is very slow when accessing VM
Solution = more RAM

2. Provides and Manages System Security
Single-user Operating
Systems
● minimal security
● user has full authority
Server Operating Systems
● login and password capability
● protection of user’s data
stored on the server’s central
hard disk drives
● protection and security for
software programs

3. Provides the System Interface
System Interface or shell =
the interface between the
user and the computer
Command Line Interface
(CLI)
● Linux, UNIX, DOS, older
OS’s
Graphical User Interface
(GUI)

Command Line Interface
DOS, UNIX, others

4. Provides the Interface for Application Software
● Operating systems are software
● Operating systems are designed
and developed for a specific CPU
or “family of CPUs”
● Macintosh OS: Motorola
680xx, PowerPC Gx, Intel
● DOS: Intel CPUs
● Windows 9x and XP: Intel
80386, 80486, and Pentium
CPUs
● Linux: Intel CPUs
● MS NT & 2000: Intel CPUs

4. Provides the Interface for Application
Software (continued)
● Application software is developed for an
operating system
MS Word for Windows XP
● Windows XP
● Intel CPU
MS Word for the Macintosh
● Macintosh OS X
● Gx CPU or Intel CPU

Compatibility
Question
Will software developed for one operating system work on another? Will
MS Word for Macintosh run on a PC with Windows XP?
Answer
No (unless there is special emulation software or hardware). The software
must be developed separately for each operating system.
Much of this is beginning to change with MAC using the Intel CPU.

Order of Development
1. The CPU
2. Other Hardware
Components
3. Operating
System Software

History of Operating Systems
1940’s – 1950’s
● Each program (job) required
significant preparation of equipment.
● Mounting tapes
● Loading punch cards
● Computer Operator – Person who
operated the computer.
● Mount tapes
● Load punch cards
● Take printouts off of printer
● Batch processing – The execution of
jobs by collecting them in a single
batch, the executing them without
further interaction with the user.

● Job queue – Jobs residing in mass
storage (hard disk drives, tape)
waiting for execution.
● FIFO (First-In, First-Out)
● Job Priorities and scheduling
● Job Control Language (JCL) –
Set of instructions explaining the
steps of a particular job.
● Operating system sent these to
the printer
● Computer Operator follows the
instructions

● Disadvantage to Batch Processing
– No interaction with the user.
● Fine for software that does not need
user interaction:
● Payroll systems (creating checks)
● Reporting systems
● Does not work well for other types of
software:
● Word processing
● Reservation systems
● Gaming

● Newer Operating Systems
● Used remote terminals and
interactive processing
● Computer must be fast enough to
coordinate with the needs of the
user.
● Real-time processing - Computer
must execute tasks under a deadline.
● Time sharing – Provides service to
multiple users at the same time.
● Multiprogramming - Time
divided into intervals.
● Multitasking – One user executing
numerous tasks (programs)
simultaneously

Today’s Operating Systems
● Today’s CPUs (multiprocessors)
● Multiple processors
● Load balancing
● Dynamically allocating tasks to
the various processors so that
all processors are used
efficiently.
● Scaling
● Breaking tasks into a number
of subtasks equal to the
number of processors
available.
● The Network (Internet)
● Becoming a single
network-wide operating
system rather than a network
of individual operating
systems.

Chapter 1-2 _ Operating Systems.pdf

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