Download Computer Org. Lecture 19 Name:_______________

Computer Org.
Lecture 19
Name:_______________
1. Suppose you are shopping for a new laptop computer, what criteria would you use to compare different
models?
2. Chapter 6 deals with performance. In the past, computer performance increases have been due to Moore’s
law (Gordon Moore - cofounder of Intel) - observation/prediction that the number of transistors that could be
put on a single chip would double every year (later changed to 18 months).
a) What kind of curve (# transistors vs. time)
does Moore’s law predict? (linear, quadratic,
exponential, etc.)
b) Why might Moore’s law not be valid in the
future?
c) As gate density increases on a chip, why would clock speed increase?
Computer Performance Terminology:
a) Efficiency =
total time executing useful work optimal time
= actual time
total time
b) Throughput - amount of work performed per unit time
c) Latency - wait time between the activation of an operation and its actual start (alternatively: time from
activation of an operation until the completion)
performance of A execution time on B
d) Relative Performance of Computer A to B = performance of B = execution time on A
execution time on reference machine
Speedup ratio = execution time on improvement machine
Lecture 19 Page 1
Computer Org.
Lecture 19
Name:_______________
e) Benchmark - suite of programs and data run on computers to compare execution times
f) Rate - rate at which tasks are executed. (e.g., Quake frames per second)
2. Comment on the quality of each metrics used to measure computer performance:
a) clock rate
b) MIPS (millions of instructions per second)
c) MFLOPS (millions of floating point operations per second)
d) CPI - (Clock cycles per instruction)
3. On way to speedup a program is to parallelize part of it (e.g., use multiple core on the same program). You
can estimate the expected speedup using Amdahl’s law.
Let’s develop Amdahl’s law using the above picture:
ts is the single processor time
fs is the fraction runs on single processor
fp is the fraction runs on p processors
Tp is the execution time on parallel system with p processors
Tp =
Speedup, S =
Lecture 19 Page 2
Computer Org.
Lecture 19
Name:_______________
4. From the above graph, what architectural improvements seem to have the biggest impact on performance?
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