Memory

1
Memory Hard Drive ManagementChapters 6 9

• David Turton
• Conestoga College
• Institute of Technology Advanced Learning
• http//www.conestogac.on.ca/dturton
• Doon 1D17 x3610

2
Early Memory Decisions (DOS)

• "no-one needs more than 640KB of memory"
• early 20-line busses max addresses 2201,024K1M
• conventional memory 0-640K
• O/S, applications, data
• upper memory 640K to 1024K
• BIOS, device drivers
• eg 640K to 768K for video (128KB Pong in BW?)
• extended memory above 1024K
• gt24 address lines in bus available
• Needed an extended memory manager
• Code/data was swapped down to conventional to
  execute
• Aberration 1st 64K un-allocated
• "High Memory" for parts of O/S (eg mouse
  driver)

3
DOS Memory Map

• This is a map of memory addresses
• Not physical RAM
• Video/network cards
• Responded to an assigned range of addresses
• Physical RAM
• Responded to a disjoint address range

4
Implications(other than BillG getting
embarrassed)

• O/S, applications and data had to fit in 640K
• programs cannot have contiguous data space
• couldn't run past 640K because of video
• video ROM hard-coded to fixed address range
• finite number of devices
• only so many address ranges available
• device memory conflicts frequent modem/COM
  ports, etc.
• devices couldn't grow larger
• video range is 128K, period.
• some applications (Lotus123) had own memory
  manager
• To manage data files 1M or larger
• WordPerfect had to write own memory manager

5
Windows 9x

• O/S lives in extended memory
• conventional upper memory available for 16-bit
  apps
• Virtual Memory
• swap file (or page file) on hard drive
• used as an extension to memory
• swaps 4K pages between physical memory swap
  file
• Unused code/data to disk, active code to memory

6
Virtual Memory Problems

• RAM is faster than hard drive, no seek time
• SATA 1.0 150MB/sec
• PC3200 (400MHz) 3.2GB/sec (20x faster)
• the more paging you do, the slower you go.
• thrashing
• RAM is continually full, continually paging
• CPU wasting time, high disk usage, slow response
• solutions
• Close applications
• Increase RAM
• Page file to another hard drive
• On another EIDE cable

• Increasing RAM
• Business app score
• Mult. applications open
• Multimedia score
• Editing media files
• 128MB ? 256MB
• Business 33 gain
• Multimedia 50 gain
• 128MB ? 512MB
• Business 8 gain
• Multimedia 10 gain
• 512MB ? 1GB
• Business 5 gain
• Multimedia 7 gain

7
NT/2000/XP/2003 Memory Management

• Eliminated fixed memory ranges
• lost some backward compatibility
• Each application has a virtual memory range
• Each range starts at byte 1
• Grows in allocations of 4K pages
• Virtual Memory Manager
• between application/driver physical memory
• pages in out of virtual memory
• app asks for address 256
• VMM delivers might actually be address 5285 in
  RAM

8
This is one reason programs cant work in REAL
MODE Not enough memory for everyone. PROTECTED
MODE hides physical limitations, allows O/S to
give everyone everything they need.
Windows NT Virtual Memory Manager
memory space for application 1
Application1
Physical RAM
memory space for application 2
Application2
pagefile.sys
9
Improving Virtual Memory

• should be 2.5x RAM size
• or more
• make max and min page file size same
• prevents file growing on demand
• and fragmenting
• move page file to another physical disk
• I/O to memory simultaneous with I/O for data
  apps

10
Memory Errors

• recurring errors/lockups
• "General Protection Fault"
• "exception fault 0E at gtgt0137BFF9C0D"
• causes
• virus
• update run AV, download patches
• memory modules faulty
• Run test utilities (memtest86)
• Pull/swap DIMMs one at a time, retest
• Not enough RAM
• Not enough free space on system disk

11
Supporting Hard Drives
12
Emergency Start-up Disksincludes utilities to
troubleshoot a failed hard drive or at least
see if you can salvage something outlook.pst?

• Win 9x
• Single bootable diskette
• Utility programs fdisk, format, extract, etc.
• Compressed cabinet file (ebd.cab)
• Uncompressed to RAM drive at boot
• Can pick individual programs w/ extract.exe
• extract ebd.cab /d list files
• extract edb.cab fred.txt extract single file
  fred.txt
• control panel ? add/remove progs ? startup disk
• Win 2000 - 4 diskettes, includes O/S kernel
• Win XP - backup file boot diskette

13
Win 9x rescue disk

• If can boot to A prompt
• Motherboard, CPU, memory, floppy drive, power
  supply and video system are functioning
• Check amount of memory ensure it sees it all.
• Problem is likely the hard drive
• fdisk is partition table OK?
• No can repair
• Win 9x fdisk /mbr
• Win 2000 fixmbr
• Can be used on Win XP systems
• But can't look into NTFS file system

14
File Systems (Microoft)if the file system is
not healthy, cannot use drive

• FAT16
• DOS/Win 95
• limit 2-4GB
• VFAT
• Win 3.11/95
• limit 2-4GB
• 255-byte file names
• 16-bit FAT

• FAT32
• Win 95 SP2
• limit gt32GB
• NTFS
• Win NT
• limit ??EB

15
FAT16 vs. FAT32

• File Allocation Table
• 1 pointer for each cluster on disk
• Points to next cluster for a file
• All 1's means end-of-file
• All zeros means cluster is free
• Else address of next location
• FAT16
• 16 bits per pointer
• Max value 216 65,536
• Can only be 65,534 clusters on disk
• 2GB disk
• 2,147,483,648 bytes / 65,534 clusters
• 32,700 bytes/cluster
• 5-byte file uses 32KB on disk

• FAT32
• 32 bits per pointer
• Max 232
• 4.2 billion pointers
• 80GB disk
• Still has spare pointers
• Min physical cluster size
• 1 sector or 512 bytes
• Min cluster used
• 2 sectors or 1KB

16
Disk error checks

• chkdsk c /f
• check c for errors and fix them
• from DOS prompt
• scandisk c
• older only Win 9x
• like chkdisk
• better with windows up
• defrag
• only win 9x
• defragment a drive
• debug
• try it!
• well, try the help prompt for it first

• Win XP facilities
• chkdsk still works
• need to disable some things
• else chkdsk restarts

17
Clean Boot for Windows XPMs article 310353

• run ? msconfig
• general tab
• ? selective startup
• clear
• system.ini,
• Win.ini,
• startup items,
• load system services
• services tab
• check
• Hide all Microsoft Services, Disable All
• OK ? restart

• chkdisk defrag
• keep restarting
• never finish
• need to disable
• startup programs
• settings
• drivers
• reset from clean boot
• general tab ? click Normal start-up

18
Partitioning disks

• win 9x
• fdisk /status
• partition info, all drives
• fdisk
• screens to display or modify partitions
• fdisk /mbr
• repairs a damaged MBR

• win 2000/XP
• Disk Manager
• prep a drive for 1st use
• diskpart
• similar to fdisk
• fixmbr
• similar to fdisk /mbr

formatting a disk with a file system see format
/?
19
Disk Inefficiencies

• fragmentation
• files are written to first available clusters
• larger files may be written to several groups of
  clusters
• these may be spread throughout drive
• files are still available
• but read time slowed with head movement
• cross-linked files
• clusters with more than one file pointing to them
• lost clusters
• clusters marked as in use
• but no file in FAT references them

20
Fragmentation, Lost Clusters,Cross-Linked Files
21

• Disk Defragmenter
• Collect file fragments
• rewrite in contiguous space

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23
chkdsk

• supported by all Windows versions
• "repairs" cross-linked files lost clusters
• lost clusters become "file001.chk"
• locates and flags bad sectors
• XP also has graphical version
• note needs exclusive access
• Clean boot or check before loading services

24
Freeing SpaceXP through properties on a disk
driver

• Disk Cleanup
• lists deletes temporary files
• Disk Compression
• stores data in drive in one big file
• compression algorithm uses less space
• trade-off
• more data transferred per read or write
• more CPU load to compress/decompress

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26
Caching
many slow trips
hard drive
CPU
cache program
hard drive
CPU
few slow trips
many fast trips
RAM

• RAM to hold data read from or written to hard
  drives
• cache program reads ahead of CPU
• faster from RAM than waiting for disk to move
• Hardware cache
• BIOS and RAM on drive controller
• slower bus to CPU
• software cache
• uses systems RAM
• faster bus to CPU

27
Backups

• can recover data lost to system failure, virus,
  etc.
• only if you plan ahead
• full backup
• every file very large, very slow
• incremental backup
• files changed since last backup (full or
  incremental)
• archive bit turned off
• fastest need to restore full backup and every
  incremental since
• differential backup
• files changed since last full backup
• archive bit left on
• fast need to restore full backup and only last
  differential
• Note
• XP's backup doesn't compress commercial
  products do

28
Suggested backup schedulechild parent -
grandparent
29
Scheduled TasksControl Panel ? Scheduled Tasks

• schedule tasks to run
• daily, weekly, etc.
• used by Ms backup, Norton AV
• can create a batch file
• copy certain folders
• schedule to run daily

30
Troubleshooting Hard Drives

• Norton Utilities www.symantec.com
• prevent drive damage, recover data, repair
  damage, improve performance
• use version for your O/S
• damage could result
• Partition Magic www.powerquest.com
• FAT16 to FAT32, create/resize/move partitions
• without losing data
• Great for clients that "shorted" c drive space
• hide partitions
• SpinRite www.grc.com
• DOS small footprint, real mode from floppy
• analyse drive surface, data recovery from
  corrupted files, recover file system information

31
Resolving drive problems

• invalid drive or drive specification
• Booting from C
• same message using XP boot diskette
• Partition table damaged on hard drive
• Win 9x fdisk /mbr XP fixmbr
• Invalid media type
• Non-DOS disk
• Unable to read from drive C
• O/S boot record damaged
• recover from backup copy, if have one
• repair w/ Norton disk doctor or SpinRite

32
Resolving drive problems cont'd

• Sector not found reading drive C, abort, retry,
  Ignore, Fail?
• FAT or root directory damage
• try copying important files off drive
• Norton Disk Doctor
• to repair FAT or root directory
• Non system disk or disk error
• Invalid system disk
• Win9x to recover io.sys msdos.sys
• sys C
• Win XP copy, from another machine
• ntldr, ntdetect.com, boot.ini