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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.

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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

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