Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Operating Systems

P. Healy

CS1-08Computer Science Bldg.

tel: 202727patrick.healy@ul.ie

Autumn 2019–2020

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Outline

1 Computer System Organization – §1 of SGG

2 Computer System Architecture – §1 of SGG

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Computer System Operation

One or more CPUs, device controllers connectproviding access to shared memory

Concurrent execution of CPUs and devices competing formemory cycles

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Computer Startup

bootstrap program1 is loaded at power-up or rebootTypically stored in ROM or EEPROM, generally known asfirmware

Loads operating system kernel and starts executionThe OS then starts executing the first process, such asinit

init is a system program or daemon; i.e., it providesservices on behalf of OS but is outside kernel

init loads other daemonsexample of a daemon is the “listener” program that reacts toexternal network requests e.g. ftp

OS then waits for some event to occur

1Bootstrap program is sometimes also called bootloaderP. Healy (University of Limerick) CS4023 Autumn 2019–2020 4 / 20

Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Computer Startup: Linux

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Computer System Operation

I/O devices and the CPUEach device controller (hardware) is in charge of aparticular device typeEach device controller has a local buffer (memory)CPU moves data from main memory to local buffersI/O is from local buffer of controller to the deviceDevice controller informs CPU that it has finished itsoperation by causing an interrupt

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Computer System Operation

I/O devices and the CPUEach device controller (hardware) is in charge of aparticular device typeEach device controller has a local buffer (memory)CPU moves data to main memory from local buffersI/O is to local buffer of controller from the deviceDevice controller informs CPU that it has finished itsoperation by causing an interrupt

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Common Functions of Interrupts

Interrupt transfers control to the interrupt service routinegenerally, through the interrupt vector, which contains theaddresses of all the service routines (computer code)Interrupt architecture must save the address of theinterrupted instructionIncoming interrupts are disabled while another interrupt isbeing processed to prevent a lost interruptA trap is a software-generated interrupt caused either byan error or a user request

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

I/O Structure

A device controller (hardware) maintains some localbuffer storage and a set of special purpose registersOS has a device driver (software) for each devicecontrollerStart of an I/O operation:

The loads the appropriate registers withinthe device controllerThe examines the contents of theseregisters to determine what action to takeThe device controller starts the transfer of data from/to thelocal buffer to the to/from the deviceOnce the transfer is complete, the device controller informsthe device driver via an interruptThe device driver then returns control to the OS, possiblyreturning (if the operation was a ’read’) the data or a pointerto the data

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Interrupt Timeline

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Direct Memory Access Structure

Used for high-speed I/O devices able to transmitinformation at close to memory speedsDevice controller transfers from bufferstorage directly to main memory without CPU interventionOnly one interrupt is generated per block, rather than oneper byte (as previously done)On current linux systems blocksize is bytes

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Storage Structure

– only large storage media that the CPUcan access directly (via data bus)

cache doesn’t count as it is small

– extension of main memory thatprovides large nonvolatile storage capacityMagnetic disks – rigid metal or glass platters covered withmagnetic recording material

Disk surface is logically divided into tracks, which aresubdivided into sectorsThe disk controller determines the logical interactionbetween the device and the computerBeginning to become obselete for laptops, lightweightdevices; replaced by solid-state disks

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Storage Hierarchy

Storage systems organized in hierarchySpeedCostVolatility

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Storage Hierarchy

Storage systems organized in hierarchy

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Large-Scale Storage Devices

Main memory: only large storage media that the CPU canaccess directly

Random accessTypically volatile

Secondary storage: extension of main memory thatprovides large nonvolatile storage capacityTwo of these:

Hard disks: rigid metal or glass platters covered withmagnetic recording material

Disk surface is logically divided into tracks, which aresubdivided into sectorsThe disk controller determines the logical interactionbetween the device and the computer

Solid-state disks: faster than hard disks, nonvolatileVarious technologies e.g. a mixture of RAM and magneticdiskPopular in cameras, PDAs, USB etc,; now in larger devices

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Large-Scale Storage Devices (contd.)

Dummies guide to HDD and SSD here

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Caching

Important principle, performed at many levels in acomputer (in hardware, operating system, software)Information in use (i.e., it will likely be used soon again)copied from slower to faster storage temporarilyFaster storage (cache) checked first to determine ifinformation is there

If it is, information used directly from the cache (fast)If not, data copied to cache and used there

Cache smaller than storage being cachedCache management important design problemCache size and replacement policy

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

How a Modern Computer Works

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

System Types

Traditionally, systems use a single general-purposeprocessor (from PDAs all the way to mainframes) – thoughthat is changing

Most systems have special-purpose processors as wellMultiprocessor systems growing in use and importance

Also known as parallel systems, tightly-coupled systemsAdvantages include

Increased throughputEconomy of scaleIncreased reliability: graceful degradation or fault tolerance

Two typesAsymmetric Multiprocessing (master-slave relationship)Symmetric Multiprocessing

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Symmetric Multiprocessing Architecture

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

A Dual-Core Design

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Computer System Organization – §1 of SGGComputer System Architecture – §1 of SGG

Clustered Systems

Like multiprocessor systems, but multiple systems workingtogether

Usually sharing storage via a storage-area network(SAN)Provides a high-availability service which survivesfailures

Asymmetric clustering has one machine in hot-standbymodeSymmetric clustering has multiple nodes runningapplications, monitoring each other

Some clusters are for high-performance computing(HPC)

Applications must be written to use parallelization

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