Chapter 9
This presentation is the property of its rightful owner.
Sponsored Links
1 / 35

Chapter 9 PowerPoint PPT Presentation


  • 105 Views
  • Uploaded on
  • Presentation posted in: General

Chapter 9. Managing Memory. You Will Learn…. About the evolution of OS memory management How Windows 9x manages memory addresses and virtual memory How Windows NT/2000/XP manages memory How to troubleshoot OS problems with memory. OS Memory Management Evolution.

Download Presentation

Chapter 9

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chapter 9

Chapter 9

Managing

Memory


You will learn

You Will Learn…

  • About the evolution of OS memory management

  • How Windows 9x manages memory addresses and virtual memory

  • How Windows NT/2000/XP manages memory

  • How to troubleshoot OS problems with memory

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Os memory management evolution

OS Memory Management Evolution

  • Decisions made by IBM and Microsoft in the early 1980s still affect Windows 9x memory use

  • Early CPUs had only 20 address lines

    • Largest memory address the CPU could handle was 11111111111111111111 (1,048,575, 1,024K, 1 MB)

  • DOS and applications used first 640K

  • BIOS and device drivers used 640K to 1024K

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Dos and windows 9x memory

DOS and Windows 9x Memory

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Further evolution

Further Evolution

  • Later CPUs and motherboards used 24 address lines and more

    • Memory above 1024K became available, called extended memory

  • Memory addresses expressed using hexadecimal notation

    • Upper memory address numbers begin with A through F

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


First megabyte of memory in windows 9x

First Megabyte of Memory in Windows 9x

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


How memory addresses are used

How Memory Addresses are Used

  • Memory addresses are assigned to memory and used for communication

    • Device drivers

    • The OS

    • Application software

  • All components identify data to be shared by referring to its memory address

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Data identified by its memory address

Data Identified by Its Memory Address

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Windows 9x memory management

Windows 9x Memory Management

  • Supports 32-bit, protected mode applications

  • Still permits 16-bit, real mode device drivers and applications

    • Uses a virtual DOS machine (VDM)

  • OS totally controls memory access

    • Enables the use of virtual memory, where memory is stored in swap file

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Real mode and protected mode memory access

Real Mode and Protected Mode Memory Access

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Evolution of memory management

Evolution of Memory Management

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


How windows 9x and dos manage memory addressing

How Windows 9x and DOS Manage Memory Addressing

  • ROM BIOS on the motherboard

  • Some circuit boards

  • Device drivers

  • The OS

  • Applications

Memory mapping is the process of assigning memory addresses as the PC is booted to:

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


How windows 9x and dos manage memory addressing continued

How Windows 9x and DOS Manage Memory Addressing(continued)

  • Conventionalmemory or base memory: the first 640K

  • Upper memory: from 640K to 1024K

  • Extended memory: above 1024K

  • High memory area (HMA): the first 64K of extended memory

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Memory address map

Memory Address Map

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Conventional memory

Conventional Memory

  • Designed to hold all memory addresses accessible to the user

    • Operating system

    • Application software

    • Data

  • Turned out to be grossly inadequate

  • Couldn’t be rectified in subsequent DOS versions, because upper memory had been dedicated to hardware devices

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Upper memory

Upper Memory

  • Memory addresses from 640K to 1024K

  • Video RAM and ROM

  • Sixteen-bit BIOS programs for legacy expansion boards

  • Often has unassigned addresses

    • Memory management involves using unassigned upper memory addresses for device drivers and TSR programs

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Expanded memory and the high memory area

Expanded Memory and the High Memory Area

  • Memory above 1 MB

  • Managed as a device

    • Need device driver (memory extender)

    • Need applications written to use it

  • High memory area is the first 64K

    • Exists because of a bug in Intel 286 processors

    • DOS 5 and above could store portions of the OS in the HMA

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Utilities that manage memory

Utilities that Manage Memory

  • Himem.sys is device driver for memory above 640K

    • Loaded automatically by Windows 9x

  • Emm386.exe loads device drivers and other programs into upper memory

    • Can be loaded by an entry in Config.sys

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Using himem sys

Using Himem.sys

  • Manages memory as a device

  • Loaded with a Device= command in Config.sys

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Himem sys in config sys

Himem.sys in Config.sys

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Using emm386 exe

Using Emm386.exe

  • Used to manage memory addresses in upper memory

  • Use the MEM command to examine memory allocation

    • Goal of memory management is to maximize the amount of free conventional memory

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


A pc not using upper memory

A PC Not Using Upper Memory

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Creating and using upper memory blocks

Creating and Using Upper Memory Blocks

  • Himem.sys must be loaded first

  • Emm386.exe is loaded next

  • DOS=HIGH loads DOS into HMA

  • DOS=UMB creates upper memory blocks (consecutive memory addresses in upper memory assigned to physical memory)

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Config sys set to use upper memory

Config.sys Set to Use Upper Memory

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Loading device drivers high

Loading Device Drivers High

  • Devicehigh= in Config.sys loads a device driver into a UMB

  • Loadhigh (LH) command in Autoexec.bat loads a program into a UMB

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


How windows 9x manages virtual memory

How Windows 9x Manages Virtual Memory

  • Virtual memory uses hard drive space so that it acts like memory

  • Windows stores virtual memory in a swap file

  • Increases the amount of memory available

  • Works considerably slower than real memory

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Virtual memory options

Virtual Memory Options

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Virtual memory options continued

Virtual Memory Options(continued)

  • Windows 9x automates virtual memory management

  • To improve performance, set the maximum and minimum size to same value, preventing the size from changing

  • Set size to 2.5 times amount of RAM

  • Location of the swap file can be changed

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Memory paging

Memory Paging

  • Virtual Memory Manager (VMM)

    • Page is a 4K segment of memory

    • Memory paging is the process of moving pages in and out of physical RAM

  • Symptoms of disk thrashing

    • Very high CPU use

    • Very slow system response

    • Constant hard drive use

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Windows nt 2000 xp memory management

Windows NT/2000/XP Memory Management

  • Windows NT/2000/XP eliminates the complexity of DOS and Windows 9x

    • All memory addresses used the same way

    • Loses some backwards compatibility

  • Virtual memory manager

    • Allocates memory in 4K pages

    • Swap file is named Pagefile.sys

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Windows nt 2000 xp memory management continued

Windows NT/2000/XP Memory Management (continued)

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


How windows nt 2000 xp manages virtual memory

How Windows NT/2000/XP Manages Virtual Memory

  • Set initial and maximum sizes of the file to the same value

  • Balance file size with disk space use

  • Optimize performance by moving the paging file off the boot volume

  • Paging file must be on the same disk as the OS to capture memory dumps

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Changing paging file settings

Changing Paging File Settings

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Troubleshooting memory

Troubleshooting Memory

  • Check for viruses

  • Download latest OS and application patches from manufacturer’s Web site

  • Test memory modules

    • Memtest86 can be downloaded from http://www.memtest86.com

  • Determine whether sufficient memory is installed

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


Summary

Summary

  • Evolution of OS memory management

  • Windows 9x memory address and virtual memory management

  • Windows NT/2000/XP memory management

  • Troubleshooting OS memory problems

A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition


  • Login