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Chapter 9

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

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  1. Chapter 9 Managing Memory

  2. 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

  3. 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

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

  5. 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

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

  7. 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

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

  9. 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

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

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

  12. 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

  13. 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

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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

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

  21. 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

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

  23. 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

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

  25. 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

  26. 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

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

  28. 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

  29. 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

  30. 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

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

  32. 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

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

  34. 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

  35. 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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