Storage Devices

1
Storage Devices
2
??????? Program ??? Data
Secondary Storage
????
????????????????
????????????????????????????
Primary Storage
????????
3
???????????????????? Secondary Storages
????????Files
4
????????? Files

• Executable Program File
• Graphics File
• Audio File
• Video File

• ASCII File
• Data File
• Document File
• Spreadsheet File
• Source Program File

5
?????????? File (File Accessing)

• Sequential Accessing
• Direct Accessing (Random Accessing)

6
????????????????????????

• Batch Processing
• Transaction Processing

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Batch Processing

• ????????????????????????????????? ??????????????
• ???????????? 2 files
• master file
• transaction file
• ???????? ?????????????????????

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Transaction Processing

• ?????????????????????????????????????
  ???????????? real time
• ??????????????????? real time ????????????????
  -????? ?????????????????????????? ????????????
  online

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???????? Batch Processing

• ??????????????
• ???????
• ???????????????????????????????????

10
?????????? Batch Processing

• ?????????????????????

11
???????? Transaction Processing

• ??????????????????

12
?????????? Transaction Processing

• ?????????
• ????????????????????????????????
• ??????????????? online
• ???????????

13
Batch ???? Transaction Processing?

• ???????????????????????????????????

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Secondary Storages

• ??????????????????????? Primary Storage

15
??????????????? Secondary storages

• ??????????????????
• ??????? (Economy)
• ?????????????????? (Reliability)
• ????? (Convenience)

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????????? Secondary Storages

• Sequential Access
• Magnetic Tape Storage

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????????? Secondary Storages

• Random Access (Direct Access)
• Magnetic Disk
• CD Rom
• Magneto Opitcal Disk

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????????????????????? Tape

• ???????????????? sequential
• ???????
• ????????
• ?????????

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???????????????????? Tape

• ??????????????? batch processing
• ??????????????????? (backup)

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Magnetic Disk Storage

• ?????????????????????????????? direct access
• ????????????????????????????? bits

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????????? Magnetic Disk Storage

• Floppy Disk
• Hard magnetic Disk

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??????????????????Floppy Disk ??? Harddisk
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Tracks
track 80
track 00
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Sectors
sector 01
sector 00
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Clusters
cluster
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Clusters

• ??? sectors ????????????? ?????????? sectors
  ??????
• ?????????????????????????????????????????????
• ????? cluster ?????????????????????? ??????????
  track ??????? track ??

27
??????????????? Disk ????????????????????????
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Directory File Allocation Table

• ?????? disk ??????????????????????????????????????
  ?????????????? ?????????????????????????
• Directory ?????????????
• File Allocation Table ?????????????????
• ?????????????????????????? sector 0

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???????????????????
TU

• user ??? folder ???????????????????????????(?????
  ????????? files)
• ??????????????????????? ????????????????? disk
  ????????????????? directory

IS201
AC201
IM201
HOME
FRIENDS
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File Allocation Table (FAT)
File
Cluster
paper.doc
1
Cluster Address
project.xls
2
Cluster
Track
Sector
available
3
3
1
4,5,6,7
database.mdb
4
paper.doc
5
available
6

• FAT ??????????????? file ???????????????? Cluster
  ??????????????????
• FAT ????????????????? Cluster ???? ??????? track
  ??? sector ???

available
7
available
8
31
File Allocation Table (FAT)
File
Cluster
paper.doc
1

• ??????????????? save file OS ????????? fat
  ??????? cluster ??????? ??????????? cluster ???
  3, 6, 7, 8 ???? ????????? save ?? cluster ?????
• ???????????????????????? save ?? cluster ??? 3
  ????

project.xls
2
available
3
database.mdb
4
Paper.doc
5
available
6
available
7
available
8
32
File Allocation Table (FAT)
File
Cluster
paper.doc
1

• ????????????? cluster ??? 3 ????? ??????????? FAT
  ???????????????????? ???? ??????? save ?? ?
  ???????????? ???????????????????????? 6
• ????????????? save ??????? DOS ?????????? ????
  end of file ????????????????????????????

project.xls
2
available
3
database.mdb
4
Paper.doc
5
available
6
available
7
available
8
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File Allocation Table / Directory
Cluster

• ??? Fat ???/???? Directory ???????????????????????
  ???????
• Operating System ?????????? ????????????
  Directory ??? Fat ?????????? ???????????????
  sector ???

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Harddisk

• Harddisk ????????????? ???????????????????????????
  ????????????????????? ????????????????????????????
  ??? ????????????????????? Cylinder

35
??????????????????????????????????????

• Seek time ?????????????????????? ? track
  ?????????????
• Head switching ????????????????????????? ??????
  cylinder ?????????????
• Rotational delay ??????????????????? ?
  ??????????????
• Data transfer ?????????????????????? ??? harddisk
  ?? memory ????????????????

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Harddisk ????????????? Cylinders
Cylinders
Heads
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Seek Time
Data
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Head Switching
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Rotational Delay
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????????????????? Harddisk

• Access time
• Seek time
• Head switching
• Rotational delay
• Data transfer rate

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?????????????????????? Harddisk

• Disk Defragment
• Data Compression
• Using Several Disk

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Disk Defragment

• ?????????????? file ?????????????????????????
  Hard disk???????????????

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Data Compression

• ????????????????????????? Cluster ?????? file
  ?????
• ????????????????

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???????? Data Compression

• Uncompressed Compressed
• a 00
  0
• b 01
  01
• c 10
  10
• d 11
  11
• Example abaaacad
• Before Compressed 0001000000100011 (16 bits)
• After Compressed 00100010011 (11
  bits)

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Using Several Disks

• ?????????? hard disk ?????????????????????????????
  ?????????????????????????
• ????????????? ???? disk ?????????? record
  ???????? ???????? disk ????????? ???? record
  ?????
• ????????????????? disk ???????????????????????????
  ?????????? ??? disk ????????????
  ????????????????????????? ??????????????? Disk
  mirroring

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CD Rom

• ????????????? Plastic
• ??????????????????????????????
• Track ?????????????????? (spiral)

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CD Rom

• ????????? track ?????
• ????? sector ???????????????
• Motor ??????? CD Rom ????????????????????????????

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Magneto-Optical Disk

• ????????????????????????????????? ????????
  ???????????? laser ??? CD Rom

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Magneto-Optical Disk

• ?????????????????
• ????????????????
• ????????????????
• ?????????????????? 500 MB ?????????? 5.25 ????

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???????????? Magneto-Optical Drive

• ????????
• ???????????????? ??????? Alloy ?????? Aluminum
  ????????
• ?????? laser ???????????????????????? ? ????????
  ? ???? Alloy
• ? ???????????????? Alloy ????????????????
  ????????????????????????????????????

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???????????? Magneto-Optical Drive

• ???????
• ??? laser ??????????????? ???? Aluminum
  ?????????????????
• ????????? ???????????????????? Alloy
  ?????????????????? ????????????????????????????
  ????????????? polarization ???????????????????????
  ?????? 0 ???? 1

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? ?????? 9/7/2540, 3/7/2541

• Removable Hard Disk ???? Secondary Storage
  ?????????????? ?????????
• ????????????????? Hard disk ????????
• ?????? ????? ??????????? ???
• ??????????

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??????????? Floppy Disk, Harddisk, CD Rom

• F/L Disk HDD CD Rom
• ?????? (MB) 1.44 4,000 650 MB
• ???????? ??? ??? ??????
• ???????? ??? ??? ???????
• ??????????? ????? ???????? ?????

54
??????????? Floppy Disk, Harddisk, CD Rom

• F/L Disk HDD CD Rom
• ???????? 3 ?? 5 ?? gt 10 ??
• ???? (???) 10 10,000 75
• Bytes / ??? 144,000 400,000 8,666,666