Operating SystemsWho’s in charge in there?

Types of Software

• Application Software : Does things we want to do

• System Software : Does things we need doneLow level details

Operating System

• Operating System : Software that manages the operation of a computer

• Not all computational systems have an OS– Early computers– Embedded systems

Varieties of OSes

• Embeded

Varieties of OSes

• Batch– Submit list of jobs

Varieties of OSes

• Real Time / Dedicated

Operating Systems

• PC Operating Systems– Windows– *nix• Linux• MacOS X

• Phone OSes– iOS– Android– Windows

Operating Systems

• What is Linux?https://www.youtube.com/watch?v=5ocq6_3-nEw

What do they do?

• Manage hardwareresources– Provide an abstraction– Allocate scare resources

Resource Scarcity

• Resources scarce in– Time• Processor• IO / Disk

– Space• Memory• Disk

• OS responsible for allocating scarce resources

Resources - Processes

• OS manages what process(es) are running– Programs take turns on processor• Run until time limit or need to wait• OS handles all hardware events

http://computerscience.chemeketa.edu/cs160Reader/OperatingSystems/ProcessManagement.html

Resources - Memory

• Main Memory : – Where running programs & data are stored– Computer may have ~4 or 8 billion bytes– Programs can "use" up to 200 trillion bytes

(48 bit addresses)

Virtual Address Space

• Program uses virtual addresses– Nice, orderly

• OS maps to – Main memory – Hard drive (Virtual Memory)

Other Resources

• For Keyboard, Monitor, Network, Disks, Printer, OS provides:– Abstraction:• Hides ugly details (how bits are stored on disk),

provides abstract interface ("MyEssay.doc")

– Allocation:• Who gets to use what when

Abstraction

• Abstractions provided via API (Application Programming Interface)

• Set of functions software can do

• OS API Features– Functions (blocks) to • Read files• Use a network• Draw windows• Get mouse position