OS tutoring #1

Contents




What is operating system?
History of OS
Input / Output






Storage structure






Software polling
Interrupt
Memory mapped
Cache
Locality of reference

OS basics
Process structure

Aerosystem Software Lab. @ Korea Aerospace Univ

http://asl.kau.ac.kr

What is Operating System?


An Operating System is the interface between
the users and the hardware.


It implements a virtual machine that is easier to program
than bare hardware

MOV EAX, EBX
1101011010101





An Operating System is the interface between
the users and the hardware.


It implements a virtual machine that is easier to program
than bare hardware

A=B

MOV EAX, EBX

return

1101011010101





An OS provides standard services (an interface)
which are implemented on the hardware.


Including Processes, CPU Scheduling, Memory managem
ent, File system, Networking…
UI

UI

UI

UI

UI

Device IO

Device IO

Device IO

Device IO

Device IO

Graphic

Graphic

Graphic

Graphic

Graphic

Network

Network

Network

Network

Network

File IO

File IO

File IO

File IO

File IO





An OS provides standard services (an interface)
which are implemented on the hardware.


Including Processes, CPU Scheduling, Memory managem
ent, File system, Networking…
UI

UI

UI

UI

UI

Device IO

Device IO

Device IO

Device IO

Device IO

Graphic

Graphic

Graphic

Graphic

Graphic

Network

Network

Network

Network

Network

File IO

File IO

File IO

File IO

File IO


System Call




Magician

4GB



2GB

Government

x


x


The Goal of OS


Convenient




Software engineering problem

Efficient


System engineering problem



Why study Operating System?


Abstraction





How do we give the users the illusion of infinity resource?
(CPU time, Memory, File space)

System Design


Tradeoff
Performance

Convenience

Performance

Abstraction

Simplicity

OS

Hardware

Software

Functionality


History of OS (Phase 0)


HW is a very expensive experiment, No OS


One function at a time







Computation
I/O
User think/response

Program loaded via card deck





Hardware is expensive, Humans are cheap
Simple Batch processing






Load program
Run
Print result
Dump
Start
Wait for Jobs
Load New Job

Execute Job

Yes


Next Job?

No




Overlapped CPU & I/O operations




CPU Don’t need to wait till I/O Finishes
More effective usage of Hardware





Multi-programmed batch system






Looks like programs are running simultaneously
Pick some jobs to run (scheduling)
Put jobs in memory (memory management)





Hardware is less expensive than before,
Humans are becoming expensive


Interactive Timesharing





Preemptive scheduling to maintain adequate response time
Avoid Thrashing (program swap in, out)

UNIX developed at Bell Lab





Hardware is very cheap, Humans are expensive


Personal Computer (Macintosh)




Return to simplicity
No more supporting
 Multiprogramming
 Concurrency
 Protection





Hardware are very cheap, but speed has limit
Parallel
 Distributed




Multi-core processors
GPU





Cluster
Grid
Cloud

Shared Memory
Computer

Computer
CPU

CPU

CPU

Computer
Computer



Other OS


Real-time Operating System


Often used as a control device in a dedicated application








Controlling scientific experiments
Medical imaging systems
Industrial control systems
And some display systems.

Well-defined fixed-time constraints.
Real-Time systems may be either hard or soft real-time




Hard real-time
 Failure cause injury or loss of money
Soft real-time
 Failure is not much critical than hard real-time



Input / Output


CPU and device controllers all use a common
bus for communication






Data bus
Address bus
Control bus

Ex. Put your hands up!




Put : Control
Your hands : Address
Up : Data



I/O


Synchronous I/O






CPU execution waits while
I/O proceeds
Easy to implement
Ex. Software polling

Asynchronous I/O




I/O proceeds concurrently
with CPU execution
More effective I/O
Ex. Interrupt



I/O type (Software polling)


Software polling synchronous I/O



CPU starts an I/O operation, and continuously polls
(checks) that device until the I/O operation finishes
Device controller contains registers for communication






Input, Output Register
 for data
Control Register
 to tell it what to do
Status Register
 to see what it’s done



I/O type (Interrupt)


Device controller has its own processor,
and executes asynchronously with CPU



Device controller puts an interrupt signal on the bus
when it needs CPU’s attention
When CPU receive an interrupt
1.

2.

3.

It saves the CPU state and invokes the
appropriate interrupt handler using the
interrupt vector
Handler must save and restore
software state
CPU restores CPU state



I/O type (Interrupt)


Interrupt timeline



Trap (software generated interrupt)




Kernel mode
System call



I/O Type (Memory mapped I/O)


Direct Memory Access


I/O device can transfer block of data to / from memory
without going through CPU
I/O Command

CPU
data

I/O device
data

Memory



Storage Structure


Memory is not much fast
as what we think





Tradeoff between
size and speed
So we use caching

Where to cache?




Cache up block requires a lot of time
than accessing memory
If cache miss ratio is high, no need to
use cache system
Locality of reference



Locality of Reference



Hardware, Software, Middleware



3 main process in Kernel


Scheduler




Pager





Multi-Tasking

Memory Management
Cache

Swapper


Virtual Memory



User mode, Kernel mode



Kernel has core functions.
User applications has algorithm for jobs.



Process structure


4 main area


Text




Data





Global variable
Static variable

BSS




Program Code

Heap

Stack


Function frame stack



OS tutoring #1

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