Operating Systems

Operating Systems Instructors David Browning Maggie Kirlakovsky Vishal Shah

Outline • Introduction • Computer System Components • Operating System Definition • Process Management • Process Concept • Process Scheduling • Memory Management • Background • Swapping, Paging, and Segmentation • Virtual Memory • I/O Management • I/O Hardware • Transformation of requests to hardware • Case Studies • Simplix Operating System Demo Operating Systems

What is an operating system? • Computer Hardware – basic computing resources (i.e.,CPU, memory, I/O devices) • Operating system – controls and coordinates the use of the hardware resources • Applications programs – controls how the system resources are used (i.e. compilers, video games) • Users (people, machines, other computers) Operating Systems

Operating System Services Program Execution File-system Manipulation I/O Operations Services Communications Error Detection Operating Systems

Outline Process Memory I/O • Introduction • Computer System Components • Operating System Definition • Process Management • Process Concept • Process Scheduling • Memory Management • Background • Swapping, Paging, and Segmentation • Virtual Memory • I/O Management • I/O Hardware • Transformation of requests to hardware • Case Studies • Simplix Operating System Demo Operating Systems

Process Concept Process Memory I/O • Process Definition • Running program • Process state • new • running • waiting • ready • terminated Operating Systems

Process Concept Process Memory I/O The Process Control Block (PCB) • Process state • Program counter • CPU registers • CPU scheduling information • Memory-management information • I/O status information Operating Systems

Process Concept Process Memory I/O CPU switch from process to process • Process (Context) Switch Operating Systems

Process Scheduling Process Memory I/O • Scheduler: Processes execution decisions • Preemptive and Nonpreemptive Scheduling • Scheduling criterion • Fairness • Efficiency • Response time • Turnaround • Throughput Operating Systems

FIFO Scheduling P1 P2 P3 0 24 27 30 Process Memory I/O ProcessBurst (Completion) Time P1 24 P2 3 P3 3 • Suppose that the processes arrive in the order: P1 , P2 , P3 The Gantt Chart for the schedule is: • Waiting time for P1 = 0; P2 = 24; P3 = 27 • Average waiting time: (0 + 24 + 27)/3 = 17 Operating Systems

FIFO Scheduling P2 P3 P1 0 3 6 30 Process Memory I/O Suppose that the processes arrive in the order P2 , P3 , P1 . • The Gantt chart for the schedule is: • Waiting time for P1 = ?;P2 = ?; P3 = ? • Average waiting time: ? Operating Systems

Priority Scheduling Queue headers Runnable Processes Highest Priority Priority 4 Priority 3 Priority 2 Lowest Priority Priority 1 Process Memory I/O • A priority number (integer) is associated with each process • The CPU is allocated to the process with the highest priority (smallest integer  highest priority). • Problem  Starvation • Solution  Aging Operating Systems

Round Robin Scheduling Current Process Next Process Current Process B F D G A F D G A B Process Memory I/O • Each process gets a small unit of CPU time – time quantum • At the end of time quantum: • process is preempted • added to the end of the ready queue. • Example Operating Systems

Multilevel Feedback Scheduling Process Memory I/O • A process can move between the various queues • Scheduler parameters: • number of queues • scheduling algorithms for each queue • method used to determine when to upgrade/demote a process • method used to determine which queue a process will enter when that process needs service Operating Systems

Background Process Memory I/O • Program must be brought into memory and placed within a process for it to be run. • Input queue – collection of processes on the disk that are waiting to be brought into memory to run the program. • User programs go through several steps before being run. Operating Systems

Main Memory Process Memory I/O • Operating system responsibilities • Keep track of which parts of memory are currently being used and by whom. • Decide which processes to load when memory space becomes available. • Allocate and deallocate memory space as needed. Operating Systems

Instruction and Data Binding Process Memory I/O • Central idea of memory management • Concept: logical address bound to separate physical address • Three possible stages • Compile time • Load time • Execution time Operating Systems

Memory Management Unit (MMU) Process Memory I/O • Hardware device that maps virtual addresses to physical addresses • Implemented with relocation register • User programs deal with logical addresses only; they never see the real physical address Operating Systems

Swapping Process Memory I/O • Temporary process shifting • “old” processes out • “new” processes in • Backing store • Fast disk • Large enough to accommodate copies of all memory images for all users • Provides direct access to these images Operating Systems

Contiguous Allocation Process Memory I/O • Two partitions of main memory • Resident operating system in low memory • User processes in high memory • Single-partition • Relocation register • Protect user processes from each other • Protect operating system code and data • Limit register • Contains range of logical addresses • Multiple partition • Multiple blocks of available memory, or holes • Incoming processes allocated memory from hole large enough to accommodate them Operating Systems

Single Partition Hardware Process Memory I/O Operating Systems

Contiguous Allocation (cont.) Process Memory I/O • Operating system responsibility • Maintain partition information • Allocated partitions • Free partitions (holes) • Allocation Algorithms • First-fit • Best-Fit • Worst-Fit Operating Systems

Allocation Example Process Memory I/O OS OS OS OS process 5 process 5 process 5 process 5 process 9 process 9 process 8 process 10 process 2 process 2 process 2 process 2 Operating Systems

Paging and Address Translation Process Memory I/O Paging and Address Translation with TLB Paging and Address Translation Operating Systems

Page Faults and Replacement Process Memory I/O Page Replacement Process Page Fault Handling Operating Systems

Page Replacement Algorithms Process Memory I/O • First-In First-Out (FIFO) Algorithm • Optimal Algorithm • Least Recently Used (LRU) Algorithm • Second Chance (Clock) Algorithm Operating Systems

Example: FIFO Algorithm Process Memory I/O 6! • 3 Frame Memory • 3 pages can be in memory at a time per process • Reference String: 7,0,1,2,0,3,0 • How many page faults? Operating Systems

Thrashing Process Memory I/O • Thrashing  a process is busy swapping pages in and out. Operating Systems

Segmentation Process Memory I/O • Memory-management scheme that supports user view of memory • Programs can be broken into logical segments, as follows: • Main program • Procedure • Method • Objects • Variables • Stack • Array • Etc. Operating Systems

Segmentation Architecture Process Memory I/O • Logical address two tuple • <segment #, offset> • Segment table • Maps two-dimensional physical addresses • Base  starting physical address in memory • Limit  specifies length of segment Operating Systems

Segmentation Example Process Memory I/O Operating Systems

What Is I/O? Process Memory I/O I/O is one of the main functions of an OS • Issues commands • Catches interrupts • Handles errors • Interface Operating Systems

I/O Hardware Process Memory I/O • ECEs -> chips, wires, power supply … • CS -> commands that HW accepts, the functions it carries out, and errors reported • Two parts • Devices • Device controller • Communicates with OS • A model for connecting the CPU, memory, controllers and I/O devices Operating Systems

Life Cycle of An I/O Request Process Memory I/O Operating Systems

Outline Process Memory I/O • Introduction • Computer System Components • Operating System Definition • Process Management • Process Concept • Process Scheduling • Memory Management • Background • Swapping, Paging, and Segmentation • Virtual Memory • I/O Management • I/O Hardware • Transformation of requests to hardware • Case Studies • Simplex Operating System Demo Operating Systems

Windows 2000 Windows Linux • 32-bit multitasking OS for Intel microprocessors • System goals • Portability • Security • POSIX compliance (IEEE 1003.3 standard) • Multiprocessor support • Extensibility • Compatibility with MS-DOS and ms-windows applications Operating Systems

Windows 2000 Architecture Windows Linux Operating Systems

Virtual Memory Manager Windows Linux • Page-base management scheme • Two step process to allocate memory • Reserves a portion of the processor’s address space • Commits the allocation by assigning space in the 2000 paging file • Automatically reclaims allocated memory when a process terminates Operating Systems

Virtual Memory Layout Windows Linux Operating Systems

I/O Manager Windows Linux • Responsible for • file systems • cache management • device drivers • network drivers • Works with VM Manager to provide memory-mapped file I/O • Controls the 2000 cache manager • Synchronous and asynchronous operations Operating Systems

Linux Basics Windows Linux • Main design goals are speed, efficiency, and standardization • Compliant with POSIX documents Operating Systems

Process Management Windows Linux • Process control block • Process properties fall into three groups • Identity • Environment • Context • Scheduling • Virtual memory Operating Systems

Scheduling Windows Linux • Running and interrupting of processes • Linux adds kernel tasks • Requested by a running process • Execute internally on behalf of a device driver. Operating Systems

Process Scheduling Windows Linux • FIFO and Round-robin real-time scheduling • Runs the process with the highest priority • Continue to run until they either exit or block Operating Systems

Memory Management Windows Linux Buddy-Heap Algorithm Operating Systems

Input/Output Windows Linux • Two caches disk access • Page cache • Buffer cache • Three device classes • Block • Character • Network Operating Systems

Outline Simplix • Introduction • Computer System Components • Operating System Definition • Process Management • Process Concept • Process Scheduling • Memory Management • Background • Swapping, Paging, and Segmentation • Virtual Memory • I/O Management • I/O Hardware • Transformation of requests to hardware • Case Studies • Simplix Operating System Demo Operating Systems

Operating Systems