IT_Chapter_6B

Drive Performance

• Average access time

– Also known as seek time

– Time to find desired data

– Measured in milliseconds

– Depends on two factors

• RPM

• Time to access a track

– Hard drive between 6 and 12 ms

– CD between 80 and 800 ms

• Data transfer rate

– How fast data can be read

– Measured in Bps or bps

– Hard drive ranges from 15 to 160 MBps

– CD ROMS depend on X factor

• 24x CD transfers 24 x 150 KBps

– Floppy disks transfer at 45 KBps

Optimizing Performance

• Disk optimization

– Handled by operating system tool

– Routine disk maintenance

– Optimization should be run monthly

• Clean up unnecessary files

– Delete temp files

– Uninstall unused programs

– Delete obsolete data files

– Files should be cleaned weekly

• Scan a disk for errors

– Bad spots on the media

– Find and fix the error

• Move data to a good spot

• Mark the spot as bad

– Disks should be scanned monthly

• Defragment a disk

– Files fragment when resaved

– Fragmented files load slower

– Defragment puts the fragments together

– Disks should be defragged monthly

• File compression

– Shrinks the size of a file

– Takes up less space on disk

– Reduce a disks performance

– Will increase disk capacity

– PKZip, WinZip and WinRAR

Drive Interface Standards

• Interface

– How the device is connected

– Drive controllers allow transfer of data

– Dictates transfer rate and access time

• Enhanced Integrated Drive Electronics

– EIDE

– Generic term for drive controllers

– Several names

• Fast IDE

• Advanced Technology Attachment (ATA)

– Up to 2 devices per controller

– Most computers have 2 EIDE controllers

• Small Computer System Interface

– SCSI

– Higher transfer rates than EIDE

– More than 40 devices per SCSI controller

• Computers may have several SCSI controllers

– Many versions exist

• Versions are typically incompatible

– Found in servers and workstations

• USB and FireWire

– External drives

– Transfer rate is limited

– Many devices can be connected