Secondary Storage

1
Secondary Storage

• ?????????????? ??? ???????????????????????????????
  ??? ???? ?????????????????????????????????????????
  ???
• ?????????????? Input ??? Output
• ?????????? ??? ???????????????????????????????
• Magnetic
• Optical
• ?????????????????????
• ??????
• ??????????????????-???? ??????

2
Secondary Storage Device

• Magnetic storage ?????????????????????????????????
  ???????????
• Floppy Disk
• Hard Disk
• Magnetic Tape access ??? Sequential , ???
  access ????????
• Optical Storage ???????????????? ???? laser
  beams ???????????????????????
• CDROM , WORM
• Optical Disk
• Magneto - Optical Disks (MO)

3
History of Storage Device

• 1800s punch card
• early 1950s tape drives -gt magnetic drums
• 1957 The first hard drive ( IBM's RAMAC 350
  ) 50 x 24 disks to store five megabytes
• early 1980s The first 5.25 hard disk drives , 5
  -10 MB
• The first PCs Floppy - 8 -gt 5 -gt 3.5

4
Diskette

• size 3.5 , 5 1/4 , ...
• Track , Sector
• Single-Sided, Double Sided , Double Density, HD
• Format - ?????? Diskette ????????????????????????
  ?? ????????? Track, Sector
• Cluster ??? ?????????????????????????????????????
  ???? file ??????
• FAT ( File Allocation Table)
• Access Time Seek Time Rotational Delay
  Data Transfer Rate

5
Harddisk

• Capacity Cylinders x Track/Cylinder x
  Sectors/Track x Bytes/Sector

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6
???????????????? Disk Capacity

• 1.) DISK ???? 3 1/2 , 2 sides , 80 Tracks ,
  18 sectors / Track , 1 sector 512 bytes
• Capacity 512 x 18 9216 Bytes / Track
  512 x 18 x 80 737280 Bytes/Side
  2 x 512 x 18 x 80 1474560 Bytes/????
  1474560 /1024 1440 Kbytes

7
????????? Harddisk

• Fixed
• Removable
• Portable

8
???????????????? Harddisk Capacity

• 1.) Harddisk ???? 1632 Cylinders , 12 sides ,
  1 sector 512 bytes, 54 sectors / Track
• 1632 Cylinders 1632 Track Capacity 1632 x
  54 x 512 x 12 541,458,432 Bytes
  528,768 KBytes

9
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10
CDROM

• Compact Disk Read Only Memory
• ???????????????? 4.75 ???? (12 cm.) ,
  ????????????? gt 15??
• Drive Single Speed(1X) 150 Kilobyte/S , upto
  32X (_at_7/7/98)
• Interface SCSI (???????) VS. EIDE(Enhance IDE)
• Typical Capacity 650 Mbytes
• Seektime 100 - 600 ms

11
??????????? CD-ROM

• CD-ROM ----gt ???? ??????????
  ?????????????????
• CD-R (recordable) ---gt ????????? ???????????????
  ??????????? ?????????????
• CD-RW (rewritable) ---gt ?????????????????????????
  ??

12
DVD

• Digital Video Disk
• DVD Drive ????????????????????? CD ??? ???? DVD
• ?????????????????? 4.7 GB
• ???????????????? 8.5 GB
• ?????????????????????? 9.46 GB
  ??????????????????????????????????????????????????
  ??
• ???????????????????? 17 GB

13
Storage ???? ?

• ????????????????????????????????? 2 ?????

14
Data Compression

• ??????????????? ?????????????????????????????????
  ???????
• ???? ????????????????????????????????????????????
  Early to bed, early to rise, makes a man
  healthy, wealthy and wise_at_ bed, _at_ r, kes a
  n h, w and w _at_ early , to , ise
  , ma , ealthyCompression ratio 56/30
  1.9 1 (46)
• ??????????? 2 ?????? ???
• Lossless ????????????? ? ?????????? compress
  ????????????????????? Text , Numeric
• Lossy ?????????????????????????? ?????????????
  Compression ratio ????????? ????????????????????
  ????????????????????? Video , Sound , Image