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Operating Systems
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What is an operating system?
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The operating system: A collection of programs that
manages and controls applications and other software, and
coordinates the various hardware components to perform tasks
requested by the user.
• Controls both Hardware and Software
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History
Loader: first program to become part of the Operating System
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The loader took care of loading object code (binary machine code) into
memory
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Decide where to start loading
– Read first binary instruction, and store it in memory starting with the
first place
– Add up to get the next spot
– Read in the second binary instruction, and store it in memory, etc
– When done, load the program counter with the starting address. And
erase itself from memory.
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BUT: Programs ran one at a time.
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Later: How about stacking all jobs together?
– separator card, indicates where one job stops and the next began
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So a program was created to do job management and to load the next job
each time it read the special indicator cards.
Beginning of the operating system
EXAMPLES: Mac OS, MS Windows, MS DOS, UNIX, Linux
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BIOS
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BIOS (Basic Input Output System)
• Small unchangeable part of the operating system in the ROM.
• ROM: Read Only Memory
– retains instructions even without electricity – non-volatile
• RAM: Random Access Memory
– erased when power is off –volatile
• Start button  position 00000 of BIOS memory, begin executing.
• BIOS:
– BIOS loads the rest of operating system into RAM and turns
control of the computer over to it.
– We say it Boots the System
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Booting the Computer
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Load the OS
Cold boot:
• Starting up the computer by turning the power on.
• Operating system in ROM looks for and loads the remaining
operating system into RAM.
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Warm boot:
• Reloads the operating system into RAM without disrupting
the power to the disk drives or power supply.
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Some Tasks of OS
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Tasks of the OS
Loads programs
Does Job control (management)
BIOS
Device Drivers:
• special software that enables the computer to communicate
with peripheral
• You can update the Operating System by adding a new device
driver (for a new printer)
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User Interface
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User interface: The part of the operating
system that the user sees and communicates
with. Two ways
• GUI (Graphical User Interface) - Icons (graphical
representation of command choices) are selected using an
input device, usually a mouse.
• Command line - Commands are typed in using the keyboard.
– Example: >copy c:paper.txt a:*.*
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Files and File Management
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File: the name given to any program or chunk of data
that is stored on floppy, hard disk. CD ROM, or other
storage.
• Extensions: A 3-letter extension is added to the file name
separated by a period.
– Helps the operating system identify the type of file.
– OS then knows what program to load to open the file
when you double click on the file
– Example: index.htm identifies a document called index
that is made up of HTML code.
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Files and File Management
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File System:
• Hierarchical File system organizes files in a treelike structure
or hierarchy. Organizes files into groupings folders
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Input & Output of Information Device Control
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Installing a new device:
• A physical connection must be made to the peripheral.
• The proper software drivers must be added to the operating
system
– Device Driver: A program that will allow communication
between the operating system and another part of the
computer, usually a peripheral device like a printer or
scanner. It is an addition to the operating system.
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Memory Concerns:
Cache and Virtual Memory
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If the primary memory were as large as ever needed
and as fast, the following ideas would not be
necessary.
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Cache memory: Used when the speed of memory
access is too slow - can’t keep up with the CPU’s
needs.
• Very fast memory used by the operating system to house the
data and instructions that are currently being used.
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Memory Concerns:
Cache and Virtual Memory
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Virtual Memory - addresses the problem of a program
being too big to fit into the available RAM.
• The operating system divides the program into pieces.
• The pieces are stored on the hard disk as if it were additional
RAM memory needed by the program.
• The pieces are retrieved into RAM as needed.
• Disadvantage: This slows the system down, because retrieval
of information from the disk is time consuming.
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Multitasking
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Allows several application programs to be in
RAM memory at one time.
• Allows the operating system to control more than one
program simultaneously.
• Each program “stealing” CPU time.
– Example: Playing a game while a large document is being
printed.
• In a multiprocessor system the OS also allocates jobs to keep
each of the CPU’s busy
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Summary
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An Operating System is a collection of programs
Basic tasks of OS
BIOS and booting of OS
GUI and command line interfaces
Cache and Virtual Memory
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