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1/18/2008 CSCI 315 Operating Systems Design 1
Computer System Structures
Notice: The slides for this lecture have been largely based on those accompanying the textbook Operating Systems Concepts with Java, by Silberschatz, Galvin, and Gagne (2007). Many, if not all, the illustrations contained in this presentation come from this source.
1/18/2008 CSCI 315 Operating Systems Design 2
Memory Layout for a Simple Batch System
Operating System
User Program AreaOne programs: it’s loaded, runs to completion, and leaves the system.
1/18/2008 CSCI 315 Operating Systems Design 3
Multiprogrammed Batch Systems
Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them.
Operating System
Job 1
Job 2
Job 3
Job 4
0
512K
1/18/2008 CSCI 315 Operating Systems Design 4
OS Features Needed for Multiprogramming
• I/O routine supplied by the system.• Memory management – the system must
allocate the memory to several jobs.• CPU scheduling – the system must choose
among several jobs ready to run.• Allocation of devices.
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Time-Sharing SystemsInteractive Computing
• The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory).
• A job swapped in and out of memory to the disk.• On-line communication between the user and the
system is provided:– When the operating system finishes the execution of one
command, it seeks the next “control statement” from the user’s keyboard
• On-line system must be available for users to access data and code.
1/18/2008 CSCI 315 Operating Systems Design 6
Desktop Systems
• Personal computers – computer system dedicated to a single user.
• I/O devices – keyboards, mice, display screens, small printers.
• User convenience and responsiveness.• Can adopt technology developed for larger operating
system: – Often individuals have sole use of computer and do not need
advanced CPU utilization of protection features.
• May run several different types of operating systems (Windows, MacOS, UNIX, Linux).
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Parallel Systems
• Systems with more than one CPU in close communication (also known as multiprocessor systems).
• 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 (in some cases)
• graceful degradation
• fail-soft systems
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Parallel Systems (Cont.)• Asymmetric multiprocessing
– Each processor is assigned a specific task; master processor schedules and allocated work to slave processors.
– More common in extremely large systems.
• 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.
1/18/2008 CSCI 315 Operating Systems Design 9
Symmetric Multiprocessing Architecture
CPU
Memory
CPU CPU...
1/18/2008 CSCI 315 Operating Systems Design 10
Distributed Systems
• 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:– Resources Sharing, – Computation speed up – load sharing,– Reliability,– Communications.
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Distributed Systems (cont.)
• Requires networking infrastructure.
• Local area networks (LAN) or Wide area networks (WAN).
• May be either client-server or peer-to-peer systems.
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General Structure of Client-Server System
Client
Server
Client Client...
network
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Clustered Systems
• Clustering allows two or more systems to share storage.
• Provides high reliability.
• Asymmetric clustering: one server runs the application or applications while other servers standby.
• Symmetric clustering: all N hosts are running the application or applications.
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Real-Time Systems
• 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.• Real-Time systems may be either hard or soft
real-time.
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Real-Time Systems (Cont.)
• Hard real-time:– Secondary storage limited or absent, data stored in
short term memory, or read-only memory (ROM).– Conflicts with time-sharing systems, not supported
by general-purpose operating systems.
• Soft real-time:– Limited utility in industrial control of robotics.– Integrate-able with time-share systems.– Useful in applications (multimedia, virtual reality)
requiring tight response times.
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Handheld Systems
• Personal Digital Assistants (PDAs).
• Cellular telephones.
• Issues:– Limited memory,– Slow processors,– Small display screens.
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Migration of Operating System Concepts and Features
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Chapter 2: Computer-System Structures
• Computer System Operation
• I/O Structure
• Storage Structure
• Storage Hierarchy
• Hardware Protection
• Network Structure
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A Modern Computer System
CPUDisk
ControllerI/O
Controller
...
Disks Mouse
Keyboard
Printer
Memory Graphics Adapter
Network Interface
Monitor
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Computer-System Operation
• I/O devices and the CPU can execute concurrently.• Each device controller is in charge of a particular device
type.• Each device controller has a local buffer.• CPU moves data from/to main memory to/from local
buffers.• I/O is from the device to local buffer of controller.• Device controller informs CPU that it has finished its
operation by causing an interrupt.
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Common Functions of Interrupts
• Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines.
• Interrupt architecture must save the address of the interrupted instruction.
• Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt.
• A trap is a software-generated interrupt caused either by an error or a user request.
• An operating system is interrupt driven.
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Interrupt Handling
• The operating system preserves the state of the CPU by storing registers and the program counter.
• Determines which type of interrupt has occurred:– polling,– vectored interrupt system.
• Separate kernel routines determine what action should be taken for each type of interrupt.
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I/O SystemsI/O subsystem hides peculiarities of
devices from rest of system. It contains:
• Memory management component
• General device driver interface
• Drivers for specific hardware devices
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DMA Structure
• Used for high-speed I/O devices able to transmit information at close to memory speeds.
• Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention.
• Only on interrupt is generated per block, rather than the one interrupt per byte.
1/18/2008 CSCI 315 Operating Systems Design 25
Storage Structure• Main memory – only large storage media that the CPU
can access directly.
• Secondary storage – extension of main memory that provides large nonvolatile storage capacity.
• Magnetic disks – rigid metal or glass platters covered with magnetic recording material:– Disk surface is logically divided into tracks, which are subdivided
into sectors,– The disk controller determines the logical interaction between
the device and the computer.
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Storage Hierarchy
• Storage systems organized in hierarchy:– Speed,– Cost,– Volatility.
• Caching – copying information into faster storage system; main memory can be viewed as a last cache for secondary storage.
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Caching
• Use of high-speed memory to hold recently-accessed data.
• Requires a cache management policy.
• Caching introduces another level in storage hierarchy:– This requires data that is simultaneously stored in
more than one level to be consistent.
1/18/2008 CSCI 315 Operating Systems Design 28
From Disk to Register
Consider a system with virtual memory in which an integer variable A has been swapped out of “core” and currently resides on disk. Consider that a machine instruction moves that variable from memory into a register.
Question: What is the sequence of events that ensues until the value of A is finally stored in a register?