A+ Guide to Software Managing, Maintaining and Troubleshooting THIRD EDITION Chapter 9 Managing Memory

2A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

3A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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 (1,048,575, 1,024K, 1 MB) DOS and applications used first 640K BIOS and device drivers used 640K to 1024K

4A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition DOS and Windows 9x Memory

5A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

6A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition First Megabyte of Memory in Windows 9x

7A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

8A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Data Identified by Its Memory Address

9A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

10A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Real Mode and Protected Mode Memory Access

11A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Evolution of Memory Management

12A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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:

13A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition How Windows 9x and DOS Manage Memory Addressing (continued) Conventional memory 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

14A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Memory Address Map

15A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

16A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

17A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

18A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

19A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Using Himem.sys Manages memory as a device Loaded with a Device= command in Config.sys

20A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Himem.sys in Config.sys

21A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

22A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition A PC Not Using Upper Memory

23A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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)

24A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Config.sys Set to Use Upper Memory

25A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

26A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

27A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Virtual Memory Options

28A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

29A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

30A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

31A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Windows NT/2000/XP Memory Management (continued)

32A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition 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

33A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Changing Paging File Settings

34A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Troubleshooting Memory Check for viruses Download latest OS and application patches from manufacturer’s Web site Test memory modules  Memtest86 can be downloaded from Determine whether sufficient memory is installed

35A+ Guide to Software: Managing, Maintaining and Troubleshooting, Third Edition Summary Evolution of OS memory management Windows 9x memory address and virtual memory management Windows NT/2000/XP memory management Troubleshooting OS memory problems