Re: [理工] [os]-政大97-資科

[taco205130 (taco)]

※ 引述《b76516 (阿聰)》之銘言：
: 4. Consider a file consisting of 40 blocks. Assume that the file control block
: (and the index block, in case of indexed allocation) is already in memory.
: Calculate how many disk I/O operations are required for contiguous, linked,
: and indexed(single-level) allocation strategies, if, for one block, the
: following conditions hold. In the contiguous allocation case, assume that
: there is no room to grow in the beginning, but there is room to grow in the
: end. Assume that the block information to be added is stored in memory.
: (1)The block is added at the beginning.
: (2)The block is added in the middle.
: (3)The block is removed from the middle.
: (4)The block is removed from the end.
: 答案寫說
:    contiguous  linked  indexed
: (1)   81          1       1
: (2)   41          22      1
: (3)   38          22      0
: (4)   0           40      0


以下是我的想法 不知道對不對  大家幫忙看一下


如果先考慮題目10個blocks的話

coutigous:
(1)
    原先的     1 2 3 4 5 6 7 8 9 0

    要改成     * 1 2 3 4 5 6 7 8 9 0

    則若有n個blocks 則需要 2*n+1

(2)
    原先的     1 2 3 4 5 6 7 8 9 0

    要改成     1 2 3 4 5 * 6 7 8 9 0

    則若有n個blocks 則需要 2*n/2+1

(3)
    原先的     1 2 3 4 5 6 7 8 9 0

    要改成     1 2 3 4 5 7 8 9 0

    則若有n個blocks 則需要 2*(n/2-1)

(4)
    原先的     1 2 3 4 5 6 7 8 9 0

    要改成     1 2 3 4 5 6 7 8 9

    則不需要任何的disk動作

linked
(1)

   1>2>3>4>5>6>7>8>9>0>null

   *>1>2>3>4>5>6>7>8>9>0>null          // *.point= 1  ps:(1位置在memory)
(2)

   1>2>3>4>5>6>7>8>9>0>null

   1>2>3>4>5>6             // read until 5

           5>*>6           // *.point=5.point 5.point=*
(3)

   1>2>3>4>5>6>7>8>9>0>null

   1>2>3>4>5>6>7           // read until 6

           5>7             // 5.point=6.point

(4)
   1>2>3>4>5>6>7>8>9>0>null

   1>2>3>4>5>6>7>8>9>0     // read until 9

                   9>null  //9.point=null

index:

(1)(2)

   需更改index block內容 與 寫入增加的block

   但index block在memory  所以只須1次

(3)(4)

   只需要改index block



謝謝大家摟~



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◆ From: 163.25.118.52
推 lightergogo:index block是存在memory 所以不用I/O
→ taco205130:那降indexed(1)(2)的1次是??
→ taco205130:事就只有寫入新加的那個block嗎?
推 crazyjoe:YES
→ taco205130:喔屋我懂了!
※ 編輯: taco205130      來自: 163.25.115.23        (03/03 14:58)