OS AND DATA STO

RAGE

C S C I 1 3 0

I NS T R U C T O

R : DR . I M

A D R A H

A L

LAYERED ARCHITECTURE

LAYER OrderApplication SW: Excel & Access

2

High-order P.L.: Visual Basic 1Low-order P.L.: Assembly 3System SW: O.S. 3Machine Language 4Data Representation 5HW: Circuit Design 6

INTRODUCTION

Software is the set of all programs that run on a computer

VS Hardware : “Hard”Has a physical presence

Comes in two formsSystem Software: controls the computerApplications Software: accomplishes user-defined tasks

SYSTEM SOFTWARE

Hide complex detailsRegisters, empty memory locations, starting location of program in memory operations in ALU, etc …Assembly translation programs (Assembler/Loader)

Computer users, and even programmers, do not have to be aware of such details

System software provides this great flexibilityInterface between user and hardware

SYSTEM SOFTWARE

Makes a virtual computer which hides almost all technical details from the user resulting in user-friendly experiences

No need to worry about details such as register size of memory location of a given program

The system takes care of it AUTOMATICALLY

Applications Software

System Software

Hardware

USEREvery data or instruction works its way through: Even a simple mouse click !

SYSTEM SOFTWARE

System software comes in three formsTranslation programs

E.g. assembler Assembly to machine language

More on this issue when we study other programming languages (next chapter)

Operating systemsUtility program

Communication programs

OPERATING SYSTEMS (OS)

A collection of programs that Manages your computerDefines HOW a computer will interact with the outsidePrepares programs and their data to interact with hardware

Booted up, The OS is loaded into main memory for initializationBIOS

BIOSs held in ROM (cannot be altered)Hides all details Giving us the illusion of being the only user whose entire program is loaded into memory

OS - SECURITY

Usernames and passwords are ubiquitous in OSs to control access to computers

Care must be taken in choosing usernames and passwords Programs can be written to try all words in a dictionary in order to guess your

password Long Meaningless to others NEVER SHARE

SYSTEM LEVELYou want to control the access to some resource or

file even for authorized users (i.e. having access to the computer) (OSs provide permissions

Read, Write, Execute or NONE Per file

OS maintains a list of authorized users per file along with their permissions

OS - I/O & AUXILIARY STORAGE

Passing of information between main memory and peripheral devices

I/O & Auxiliary StorageE.g. Printers, mice, keyboards, disks, tapes, etc …

For I/O: Translation of input data to binary and output data from binary (to whatever the I/O device is using)

For secondary storage: Supervision and organization of data stored on tapes and disks (Auxiliary storage)

OS - I/O & AUXILIARY STORAGE

Writing to DisksFind empty spaceTransfer data (No translation)Update disk directory (location of new file)Update list of empty spaceAttempts to optimize the use of available space How to find the best fit for a particular file?

First available position that could accommodate the file One with close size to that of the file Split into more that one position

OS - I/O & AUXILIARY STORAGE

Deleting from diskUpdate directory onlyRemove the files entryAdd space occupied by file to available spaceA fragmented disk usually has empty space but this

space is scattered all over the disk with not much contiguity

Defragmenters

CPU ALLOCATION

Single-user systems allocate all CPU time to one user/program

Multi-user systems? Sharing main memory and CPU timeCPU is very efficient Process between millions to billions of instructions per second Other devices on the computer aren’t as fast

Printers: 100 characters per second Disks:

several milliseconds to look up address in directory several milliseconds to locate track and sector (spin disk) and position the R/W

head Physical motion will always be slower than transferring electric pulses I/O bound

A machine whose performance is limited due to I/O CPU is idle most of the time

CPU ALLOCATION

Solutions Overlapped processing

Running other programs while current is waiting for I/O Good for I/O What about short programs waiting for long ones?

Starvation Multi-tasking (multiprogramming, timesharing)

All programs requesting CPU time will have access to it in timeslices All are in memory together and are listed in a a ready queue

MULTI-TASKING

1 CPU, 1 main memory with many usersWhen the CPU has time, it picks the first in ready

queue and runs it for a timeslice Saves a snapshot of the state of the current program (CU registers) Moves on to the next one and places the old back in the ready

queueAll processes run togetherUser won’t notice because the timeslice is very

short We CAN’T perceive time spans of less than 40-50 milliseconds Shorter timelices

+ Give the illusion of continuous process - Not very good if most of time is spent on saving the snapshots (wasted

time) We need to strike a balance

PARALLEL PROCESSING

As opposed to multi-tasking1 main memory, many CPUs with many

usersJobs can be distributed among CPUsEven one job can span many CPUs each

working on some subtaskVery complex processBeyond the scope of this course

OS - MEMORY MANAGEMENT

RAM VS Hard diskAssume multitasking1 CPU, many programsCan’t all fit in memoryOS keeps list of empty space Adds to it when programs are done

Fragmentation could happen

OS - MEMORY MANAGEMENT

Compaction

OS - MEMORY MANAGEMENT

Paging Allow one program to occupy many noncontiguous memory segments

(pages)

OS - MEMORY MANAGEMENT

Swapping What if there are no pages to fit all program? Start program by loading only needed pages Swap between needed and unneeded ones

NETWORKS

We are not in isolation anymore Help computers communicate Transfer data without physical intervention (i.e. not via disk or tape) Sharing resources

5 users and all want to access a printer?LANs Limited to a single building or campusWANs Span cities, countries and even continents

NETWORK TOPOLOGIES

Ring vs. Star topologies

CLIENT/SERVER MODEL – STAR TOPOLOGY

THE INTERNET & WEB

TYPES OF CONNECTIONS

Physical connectionsTwisted-pair wire

Two insulated copper wires wrapped around each other. Transmit electrical signals US phone system

Used to form WANs

NETWORKS

Coaxial cable Insulated copper wireUsed for cable TVsFaster and less prone to interference than twisted-pair but more expensive

NETWORKS

Fiber OpticsFastestTransfer light instead of electricity No weight

Less prone to interference

Expensive to install

WIRELESS NETWORKS

Wireless (non-physical) connections Radio waves (In LANs)

Where physical wiring isn’t very convenient Prone to a lot of interference from radio transmitters

Microwaves (In WANs) Use high frequency radio signals which travel easily but only in straight lines

Relay towers must be set up at intervals or satellites must be used for larger distances

Carries more data (high frequency)

WIRELESS NETWORKS

Types of electromagnetic waves

They only differ from each other in wavelength/frequency

Wavelength is the distance between one wave crest to the next

WIRELESS NETWORKS

The potential drawbacks to a wireless solution include

Intervening hills and tall buildings or trees can block the radio frequency (RF) signals "line-of-sight“: antennas must be able to "see" each other

Severe weather, can adversely affect signal transmission

Might be susceptible to other radio frequency interference

Dense fog could possibly be a problem for microwave links

NETWORKS

BandwidthDepends on the link between two computers

Measured in bpsTwisted-pair: 10-100 MbpsFiber optic: > 2400Mbps=2.4Gbps

NETWORKS OVER THE PHONE SYSTEM

Phone systems transfer data as continual electrical signals that forms a wave

Varied frequency and amplitudeAnalog signalComputer phoneDigital to analogComputer phoneDigital to analogModemCapable of transmitting a certain number of bits per second

>14,400 up to 56K

PROTOCOLS

Is a rules that governs the transmission of data within a network

How machines are addressedHow messages are addressedWho can view or transmit a sent messageHow will the message be packed/unpacked by sender/receiver

How to deal with transmission errorsSender, receiver and intermediaries must

agree on a communication protocol before communicating

PROTOCOLS

Sender steps Layer 1: (Application) A message is usually generated by some application on the

sender Layer 2: (Packaging) The message is packaged for transmission Layer 3: (Network) routing the message to receipt Layer 4: (Physical Link) does the actual sending

PROTOCOLS

Intermediary stepsLayer 3: (Network) consulted only here

Check message and forwardLayer 4: (Physical Link) consulted only here

Does actual forwardingReceiver stepsLayer 4: (Physical Link) comes thru to next layerLayer 3: (Network) Received hereLayer 2: (Packaging) checks for any transmission errors and unpacks

Layer 1: (Application) presents to user/program