You have three different systems and you would like to compare them. You have th
ID: 3772761 • Letter: Y
Question
You have three different systems and you would like to compare them. You have the information in the table below. What system provides the lowest effective access time?
Main Memory hit
time/percentage hits
Level 1 Cache hit
time/percentage hits
Level 2 Cache hit
time/percentage hits
System A System B System CMain Memory hit
time/percentage hits
110ns 25% 112ns 20% 115ns 25%Level 1 Cache hit
time/percentage hits
15ns 40% 12ns 35% 16ns 45%Level 2 Cache hit
time/percentage hits
40ns 35% 42ns 45% 45ns 30%Explanation / Answer
System B provides the lowest Effective Acces Time.
Effective Access Time = L1 hit time * hit percentage + L2 hit time * hit percentage + MM hit time * hit percentage
(provided the miss time of L1 is included in hit of L2 and miss of L1 and L2 is included in hit time of MM)
EATA = 15 * 0.40 + 40 * 0.35 + 110 * 0.25 = 6 + 14 + 27.5 = 47.,5
EATB = 12 * 0.35 + 42 * 0.45 + 112 * 0.20 = 4.2 + 18.9 + 22.4 = 45.5
EATC = 16 * 0.45 + 45 * 0.35 + 115 * 0.25 = 7.2 + 15.75 + 28.75 = 51.7
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