IDT application note AN33 [IDT89] gives an expression for the average number of cycles per instruction in a RISC system as:
Cave = Pb(1 + b) + Pm(1 + m) + (1 ? Pb ? Pm) where:
pb = probability that an instruction is a branch
b = branch penalty
pm = probability that an instruction is a memory reference
m = memory reference penalty
Explain the validity of this expression. How do you think that it might be improved?
The first term, Pb(1 + b), is the probability of a branch multiplied by the total cost of a branch (i.e., 1 plus the
branch penalty). The second Pm(1 + m) term deals with memory accesses and is the probability of a memory
access multiplied by the total memory access cost. The final term, (1 ? Pb ? Pm), is what’s left over; that is not a
branch and not a memory access.
This formula is limited in the sense that it does not describe the difference between branches that are taken and
not taken and between cache accesses and not?cache accessed. However, its message is clear; reduce both
branches and memory accesses.
You might also like to view...
The chapter discussed defamation and how it is applied. Surf the Internet and find a defamation case (preferably one that has been decided) and write a brief summary detailing how the five criteria were applied to determine defamation.
What will be an ideal response?
Reports have three views: Report view, Layout view, and Design view
Indicate whether the statement is true or false
Find the missing coordinate for the solution to the given equation. 
A. -10 B. 0 C. 10 D. 20 E. -20
Core memory used to cost $0.01 per bit. Consider your own computer. What would be a rough estimate of the cost if memory cost is $0.01/bit? If memory were still at that price what would be the effect on the computer industry?
What will be an ideal response?