Concept

Simulation — where it appears

Replaying a recorded trace through a modelled machine, which gives a checkable second count without needing a real clock. It gives a checkable second count without needing a real clock, and the model's parameters are printed wherever a number from it appears.

Named by 2 essays across 2 fields — each of them below, with the objects they name alongside it.

The count is not the time

An operation count is exact, machine-independent, and not a running time. The gap between them is mostly memory, and it is large enough to reorder the rankings. This site carries a second count — modelled cache misses from the same runs — and asserts that the two disagree, because if they agreed the second one would carry no information.

machine · Machine

The block that is not a block

This field's model has one memory, one block size, one processor, no prefetcher, no queue and no clock, and every number in it is a count of transfers rather than a duration. A real machine has five levels, reads ahead, issues a hundred requests at once, and charges four orders of magnitude more for one kind of transfer than another. What survives the difference is worth stating exactly, and so is what does not.

wrong · Transfer

Named alongside it

The objects these essays reach for when they reach for this one.

Cost model Memory hierarchy Access pattern Block transfer Cache Comparison count External-memory model Failure mode Honest limit Locality Prefetching Quicksort

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