※ 引述《cocaincola (☆★)》之銘言：
: 1.
: Suppose a typist could type 60 words per minute continuously day after day.
: How long would it take the typist to fill a CD whose capacity is 640MB?Assume
: one word is five characters and each character requires one byte of storage.
1 word = 5 charcater, 1 character = 1 Byte
-----> 1 word = 5 Byte
-----> 1 minutes = 60 word = 300 Byte
640MB = 640 * 1024 * 1024 Byte = 2236962.13 minutes = 37282.7 hr
= 1533.4 days = 4.26 years
: 2.
: Assume a disk drive with the following physical characteristics:
: Rotation speed=12000 rev/min
: Arm movement time=0.02 msec to move to adjacent track
: Number of tracks/surface=1000(numbered 0 to 999)
: Number of sectors/track=50
: Number of characters/sectors=512
: What is the disk access time in best case,average case,and worst case?
best case --> Reading Head已經在Sector上了
1 track 有 50個sector 也就是讀完一個sector要轉0.02圈
轉一圈要1/12000分=0.005秒
---> 讀一個sector要0.0001秒 = 0.1ms
---> 0.1ms 可讀 512 character --> 5.12Mcaracter/s
Worst Case --> Reading Head要轉一圈才能讀到sector
Arm要從最裡面移到最外面才能找到track
轉一圈 --> 0.005s
Arm 移動 999個track --> 999*0.02ms = 0.01998 s
讀一個sector = 0.0001s
總共0.02508s --> 20.4kcharacter/s
Average Case
Head轉半圈 Arm移動一半
--> 0.0025s + 0.00999s + 0.0001s = 0.01259s
--> 40.67kcharacter/s
: 拜託大家了 謝謝> <
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 140.116.112.142