Transcript Abstract View of System Components

Module 1.0: Introduction
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What is an operating system?
Multiprogramming Systems
Time-Sharing Systems
Parallel Systems
Distributed Systems
Real -Time Systems
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Operating Systems
Computer System Organization
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Computer-system operation
– One or more CPUs, device controllers connect through common
bus providing access to shared memory
– Concurrent execution of CPUs and devices competing for
memory cycles
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Operating Systems
What is an Operating System?
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A program that acts as an intermediary between a user of a
computer and the computer hardware.
Operating system goals:
– Execute user programs and make solving user problems
easier.
– One purpose of OS is to hide peculiarities of hardware
devices from the user
– Make the computer system convenient to use.
Use the computer hardware in an efficient manner.
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Operating Systems
Why do we need an operating system?
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User viewpoint -- provide user interface command interpreter,
directory structure, utility programs (compilers, editors, filters)
Software developer viewpoint -- enhance the bare machine
higher-level I/O, structure files, notion of independent processes,
improved storage (size, protection)
Efficiency viewpoint -- replace a human operator scheduling jobs,
storing I/O (files), invoking necessary programs such as compiler
Economic viewpoint -- allow concurrent uses and good
scheduling of resources
So, the goals are to make the system convenient to use (via system
calls) and to manage resources efficiently.
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Operating Systems
Computer System Components
1. Hardware – provides basic computing resources (CPU, memory,
I/O devices).
2. Operating system – controls and coordinates the use of the
hardware among the various application programs for the various
users.
3. Applications programs – define the ways in which the system
resources are used to solve the computing problems of the users
(compilers, database systems, video games, business
programs).
4. Users (people, machines, other computers).
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Abstract View of System Components
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Brief History of Operating Systems
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1940's -- First Computers
1950's -- Batch Processing
1960's – IC invention -> Multiprogramming (timesharing)
1970's -- Minicomputers & Microprocessors
Late 1970's, 1980's -- Networking, Distributed Systems, Parallel
Systems
1990's and Beyond – PC’s, WWW, Mobile Systems, and hand-held
devices (PDAs), pocket PC, iPods, PS/3, Xbox, …
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Operating Systems
Why need multiprogramming? I/O Times vs.
CPU times
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400 MHz Pentium II = 400 million cycles/second
10 cycles/instruction = 40 million instructions/second
Read 1 disk block = 20 msec
CPU can do (40 x 106) / 103= 40,000 instructions/msec
Thus:
In time to read one disk block, CPU can do 20 * 40,000 = 800,000
instructions !!
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Operating Systems
Alternating sequence of CPU and I/O bursts
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Operating Systems
1960’s -- Multiprogramming and Timesharing
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Multiprogramming: CPU is multiplexed (shared) among a number
of jobs -- while one job waiting for I/O, another can use CPU.
Advantages:
– CPU is kept busy.
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Disadvantages:
– Hardware and O.S. became significantly more complex for
handling and scheduling multiple jobs.
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Timesharing: switch CPU among jobs for pre-defined time interval.
Most O.S. issues arise from trying to support multiprogramming -CPU scheduling, deadlock, protection, memory management,
virtual memory, etc.
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Operating Systems
Parallel Systems
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Multiprocessor systems with more than one CPU in close
communication.
Tightly coupled system – processors share memory and a clock;
communication usually takes place through the shared memory.
Advantages of parallel system:
– Increased throughput
– Economical
– Increased reliability
 graceful degradation or fault-tolerant
– The ability to continue providing service proportional to the level of
surviving hardware.
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Operating Systems
Parallel Systems (Cont.)
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Symmetric multiprocessing (SMP)
– Each processor runs an identical copy of the operating
system.
– Many processes can run at once without performance
deterioration.
– Most modern operating systems support SMP
Asymmetric multiprocessing
– Each processor is assigned a specific task; master
processor schedules and allocates work to slave processors.
– More common in extremely large systems
– Also used in PS/3 and Sbox
 PS/3 has 8 CPUs with one CPU acting as a master
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Operating Systems
Symmetric Multiprocessing Architecture
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Operating Systems
Distributed Systems
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Distribute the computation among several physical processors.
Loosely coupled system – each processor has its own local memory;
processors communicate with one another through various
communications lines, such as high-speed buses or telephone lines.
Advantages of distributed systems.
– Resource sharing
 sharing and printing files at remote sites
 processing information in a distributed database
 using remote specialized hardware devices
– Computation speedup – load sharing
– Reliability – detect and recover from site failure, function transfer,
reintegrate failed site
– Communication – message passing
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Operating Systems
Real-Time Systems
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Often used as a control device in a dedicated application such as
controlling scientific experiments, medical imaging systems, industrial
control systems, and some display systems.
Well-defined fixed-time constraints.
Hard real-time system. Deadline support
– Secondary storage limited or absent, data stored in short-term
memory, or read-only memory (ROM)
– Conflicts with time-sharing systems, not supported by generalpurpose operating systems.
– Examples: QNX, FreeRTOS, eCos, EROS, ChorusOS, pSOS
Soft real-time system. No deadline support
– Limited utility in industrial control or robotics
– Useful in applications (multimedia, virtual reality) requiring
advanced operating-system features.
– Examples: Linux Kurt, VxWorks, Windows CE
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Operating Systems
Network vs. Distributed OS
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Network OS
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A configuration in which there is a network of application machines, typically a
workstations with multiple server machines.
Server machines can be file servers, printer servers, mail, etc.
Each computer has its own OS. The user must be aware that there are multiple
independent machine and must deal with them explicitly.
NW OS allows machines to interact with each other by having a common
communication architecture.
Distributed OS
– A common OS shared by a network of computers
– Offers the illusion of a unified system image, i.e. single system image
 i.e, a pool of interconnected computers appears as a single unified computing
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resource
can say that these machines have a Single System Image (SSI) [Buyya vol.1, 1999].
– It provides the user with transparent access to the resources of multiple
machines
– Therefore:
 less autonomy between computers
 gives the impression there is a single operating system controlling the network.
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Research vehicle
Examples: Bell Labs Inferno & Plan 9, Mach, Amobea by Tanenbaum, Chorus by
CMU
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Further Reading
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P2P computing
Multimedia systems
Cluster computing
Blade servers
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Operating Systems