University:
California State University, Northridge
Course:
COMP 122/L | Computer Architecture and Assembly Language and Lab
Academic year:

2024
Views:

186

Pages:

56
Author:

Raquel Frost

Computer Organization and Architecture Chapter 8 Operating System Support Objectives and Functions • Convenience —Making the computer easier to use • Efficiency —Allowing better use of computer resources Layers and Views of a Computer System Operating System Services • • • • • • • Program creation Program execution Access to I/O devices Controlled access to files System access Error detection and response Accounting O/S as a Resource Manager Types of Operating System • • • • Interactive Batch Single program (Uni-programming) Multi-programming (Multi-tasking) Early Systems • • • • Late 1940s to mid 1950s No Operating System Programs interact directly with hardware Two main problems: —Scheduling —Setup time Simple Batch Systems • • • • Resident Monitor program Users submit jobs to operator Operator batches jobs Monitor controls sequence of events to process batch • When one job is finished, control returns to Monitor which reads next job • Monitor handles scheduling Memory Layout for Resident Monitor Job Control Language • Instructions to Monitor • Usually denoted by $ • e.g. —$JOB —$FTN —... Some Fortran instructions —$LOAD —$RUN —... Some data —$END Other Desirable Hardware Features • Memory protection —To protect the Monitor • Timer —To prevent a job monopolizing the system • Privileged instructions —Only executed by Monitor —e.g. I/O • Interrupts —Allows for relinquishing and regaining control Multi-programmed Batch Systems • I/O devices very slow • When one program is waiting for I/O, another can use the CPU Single Program Multi-Programming with Two Programs Multi-Programming with Three Programs Sample Program Execution Attributes Utilization Effects of Multiprogramming on Resource Utilization Time Sharing Systems • Allow users to interact directly with the computer —i.e. Interactive • Multi-programming allows a number of users to interact with the computer Scheduling • • • • • Key to multi-programming Long term Medium term Short term I/O Long Term Scheduling • Determines which programs are submitted for processing • i.e. controls the degree of multi-programming • Once submitted, a job becomes a process for the short term scheduler • (or it becomes a swapped out job for the medium term scheduler) Medium Term Scheduling • Part of the swapping function (more later…) • Usually based on the need to manage multiprogramming • If no virtual memory, memory management is also an issue Short Term Scheduler • Dispatcher • Fine grained decisions of which job to execute next • i.e. which job actually gets to use the processor in the next time slot Five-State Process Model Halted Waiting Process Control Block • • • • • • • • Identifier State Priority Program counter Memory pointers Context data I/O status Accounting information PCB Diagram Key Elements of O/S Process Scheduling Memory Management • Uni-program —Memory split into two —One for Operating System (monitor) —One for currently executing program • Multi-program —“User” part is sub-divided and shared among active processes Swapping • Problem: I/O is so slow compared with CPU that even in multi-programming system, CPU can be idle most of the time • Solutions: —Increase main memory – Expensive – Leads to larger programs —Swapping What is Swapping? • Long term queue of processes stored on disk • Processes “swapped” in as space becomes available • As a process completes it is moved out of main memory • If none of the processes in memory are ready (i.e. all I/O blocked) —Swap out a blocked process to intermediate queue —Swap in a ready process or a new process —But swapping is an I/O process... Partitioning • Splitting memory into sections to allocate to processes (including Operating System) • Fixed-sized partitions —May not be equal size —Process is fitted into smallest hole that will take it (best fit) —Some wasted memory —Leads to variable sized partitions Fixed Partitioning Variable Sized Partitions (1) • Allocate exactly the required memory to a process • This leads to a hole at the end of memory, too small to use —Only one small hole - less waste • When all processes are blocked, swap out a process and bring in another • New process may be smaller than swapped out process • Another hole Variable Sized Partitions (2) • Eventually have lots of holes (fragmentation) • Solutions: —Coalesce - Join adjacent holes into one large hole —Compaction - From time to time go through memory and move all hole into one free block (c.f. disk defragmentation) Effect of Dynamic Partitioning Relocation • No guarantee that process will load into the same place in memory • Instructions contain addresses —Locations of data —Addresses for instructions (branching) • Logical address - relative to beginning of program • Physical address - actual location in memory (this time) • Automatic conversion using base address Paging • Split memory into equal sized, small chunks page frames • Split programs (processes) into equal sized small chunks - pages • Allocate the required number page frames to a process • Operating System maintains list of free frames • A process does not require contiguous page frames • Use page table to keep track Logical and Physical Addresses - Paging Virtual Memory • Demand paging —Do not require all pages of a process in memory —Bring in pages as required • Page fault —Required page is not in memory —Operating System must swap in required page —May need to swap out a page to make space —Select page to throw out based on recent history Thrashing • • • • Too many processes in too little memory Operating System spends all its time swapping Little or no real work is done Disk light is on all the time • Solutions —Good page replacement algorithms —Reduce number of processes running —Fit more memory Bonus • We do not need all of a process in memory for it to run • We can swap in pages as required • So - we can now run processes that are bigger than total memory available! • Main memory is called real memory • User/programmer sees much bigger memory virtual memory Inverted Page Table Structure Translation Lookaside Buffer • Every virtual memory reference causes two physical memory access —Fetch page table entry —Fetch data • Use special cache for page table —TLB TLB Operation TLB and Cache Operation Segmentation • Paging is not (usually) visible to the programmer • Segmentation is visible to the programmer • Usually different segments allocated to program and data • May be a number of program and data segments Advantages of Segmentation • Simplifies handling of growing data structures • Allows programs to be altered and recompiled independently, without re-linking and re-loading • Lends itself to sharing among processes • Lends itself to protection • Some systems combine segmentation with paging Pentium II • Hardware for segmentation and paging • Unsegmented unpaged — virtual address = physical address — Low complexity — High performance • Unsegmented paged — Memory viewed as paged linear address space — Protection and management via paging — Berkeley UNIX • Segmented unpaged — Collection of local address spaces — Protection to single byte level — Translation table needed is on chip when segment is in memory • Segmented paged — Segmentation used to define logical memory partitions subject to access control — Paging manages allocation of memory within partitions — Unix System V Pentium II Address Translation Mechanism Pentium II Segmentation • Each virtual address is 16-bit segment and 32bit offset • 2 bits of segment are protection mechanism • 14 bits specify segment • Unsegmented virtual memory 232 = 4Gbytes • Segmented 246=64 terabytes —Can be larger – depends on which process is active —Half (8K segments of 4Gbytes) is global —Half is local and distinct for each process Pentium II Protection • Protection bits give 4 levels of privilege —0 most protected, 3 least —Use of levels software dependent —Usually level 3 for applications, level 1 for O/S and level 0 for kernel (level 2 not used) —Level 2 may be used for apps that have internal security e.g. database —Some instructions only work in level 0 Pentium II Paging • Segmentation may be disabled —In which case linear address space is used • Two level page table lookup —First, page directory – 1024 entries max – Splits 4G linear memory into 1024 page groups of 4Mbyte – Each page table has 1024 entries corresponding to 4Kbyte pages – Can use one page directory for all processes, one per process or mixture – Page directory for current process always in memory —Use TLB holding 32 page table entries —Two page sizes available 4k or 4M PowerPC Memory Management Hardware • 32 bit – paging with simple segmentation —64 bit paging with more powerful segmentation • Or, both do block address translation —Map 4 large blocks of instructions & 4 of memory to bypass paging —e.g. OS tables or graphics frame buffers • 32 bit effective address —12 bit byte selector – =4kbyte pages —16 bit page id – 64k pages per segment —4 bits indicate one of 16 segment registers – Segment registers under OS control PowerPC 32-bit Memory Management Formats PowerPC 32-bit Address Translation

Operating System Support

Related Documents

Recommended Documents

Description

Related Documents

Free up your schedule!

Take 5 seconds to unlock