[理工] os 恐龍版 習題 memory

[rnbjacky (浪漫A大調)]

Consider a demand-paging system with a paging disk that has an average
access and transfer time of 20milliseconds.Addresses are translated
through a page table inmainmemory, with an access time of 1microsecond
per memory access. Thus, eachmemory reference through the page
table takes two accesses. To improve this time, we have added an
associativememory
that reduces access time to one memory reference, if the
page-table entry is in the associative memory.
Assume that 80 percent of the accesses are in the associative memory
and that, of the remaining, 10 percent (or 2 percent of the total) cause
page faults.What is the effective memory access time?


我列的式子是

o.8 * 1 us + o.2 * ( 0.9 * 2 us + 0.1 *( 2 us + 20 ms )  )

假設存取associative  memory 時間是 0


請問哪邊有問題?

算不出他給的答案

(0.8) × (1 usec ) + (0.1) × (2 usec) + (0.1) × (5002 usec)


希望版上的大大可以幫忙解惑!!



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推 fxac:我同學算的跟你一樣
推 hunter0904:如果照祭祖的1us+0.18*1us+0.02*20ms吧?
→ rnbjacky:照計組的 1us+0.18*1us+0.02*( 1 + 20ms)
→ rnbjacky:不過不管哪個 都不會是解答那個  解答那個好怪= =
→ rnbjacky:1f同學是高手?
推 qpalwosk:3F嘴巴真甜>///<  1us + 0.2( 1us + 0.1*20ms )
→ qpalwosk:他的答案可能 4002寫成 5002了吧？
→ rnbjacky:原來如此 感謝！