class2 - Ts Tr Tt Tc seek time(get head to cylender...

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Sheet1 Page 1 Ts seek time (get head to cylender) Tr Rotational latency (get sector under head) Tt Transfer Time (read the data) Tc control Time (pfft) T= Tc+Ts+Tr+Tt Disk Read -maybe one block, more likely multiple blocks -two cases ( random sequences and sequential sequences) Service Demand = Sd = controller Time + (Seek Time + rotational latency+Transfer Time)*P(miss) = Tc+(Ts+Tr+Tt)*P(miss) ussually given the controller time(Tc) how to find Ts,Tr,Tt Tt= blocksize/ Transfer Rate (ie 1kBytes/20Mbits) blocksize= k=2^10 usually bytes Transfer rates = k=10^3, may be bits or bytes ##P(miss) = 1 for random requests Tsr= Seek Random (for random requests), ussually from manufacturer Trr=.5 * rotation time ##now for sequenial S_ds=Tc+(Ts+Tr+Tt)*P(miss) P(miss)=1/RunLength (ie 1st block is miss rest are not misses because we read ahead) Tss= SeekRandom/RunLength Trs = (.5 + (Run Length-1)((1+U)/2))/RunLength * Disk Revolution Time Trs = disk rev time* (.5 + (runlength-1)*.5*(1+U))/Runlength U = utilization (its a percentage 0->1.00)
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This note was uploaded on 05/02/2008 for the course ECE 460 taught by Professor Michel during the Spring '08 term at UMass Dartmouth.

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class2 - Ts Tr Tt Tc seek time(get head to cylender...

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