1p.01

1
?????
2
?????
??(cylinder)
??(sector)
??(track)
???
3
???????

• ???????
• access time seek time rotation time transfer
  time

• seek time????????????????????
• ????????????????????
• rotation time???????????????????
• ??????????????
• transfer time??????????????????
• ??? seek time ????!

4
???????

• ?????????3600rpm,????(data transfer)?????????,???
  ????(seek time)?16ms,???????3000????????????

?seek time????16ms rotational
time3600rpm???3600?
?60sec/3600?0.0167sec/?

16.7ms/? rotational time16.7/28.35ms
data transfer time3000/300000010-3s1ms
?????168.351 25.35 ms
5
???????

• ??????????5400rpm,????(data transfer)?????????,??
  ????????????????30ms,???????6000????????????

?seek time 30/2 15 ms rotational
time5400rpm???5400?
?60sec/5400?0.0111sec/?

11.1ms/? rotational time11.1/25.55ms
data transfer time6000/50000001.2x10-3s1.
2ms ?????155.551.2 21.75 ms
6
?????

• FCFS (First Come First Service)
• ????
• SSTF (Shortest Seek Time First)
• ??seek time??
• SCAN ?????
• C-SCAN ?????

7
?????

• ?????????????98, 183, 37, 122, 14, 124, 65,
  67,???????53??,????????????????????
• FCFS
• SSTF
• SCAN
• C-SCAN

1. FCFS???????? 53, 98, 183, 37, 122, 14, 124, 65,
   67 ? ??????458514685108110592640
2. SSTF???????? 53, 65, 67, 37, 14, 98, 122, 124,
   183 ? ??????12230238424259236
3. SCAN???????? 53, 65, 67, 98, 122, 124, 183, 37,
   14 ? ??????122312425914623299
4. C-SCAN???????? 53, 65, 67, 98, 122, 124, 183,
   14, 37 ? ??????122312425916923322

8
?????

• ?????????????100, 181, 39, 120, 16, 122, 67,
  69,???????55??,????????????????????
• FCFS
• SSTF
• SCAN
• C-SCAN

1. FCFS 616
2. SSTF204
3. SCAN236
4. C-SCAN