StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p>I'd just like to add a couple of finer points:</p> <ul> <li><p><strong>division</strong> is special. Since most processors can do an addition, comparison, or multiplication in a single cycle, those are all counted as one flop. But division always takes longer. How much longer depends on the processor, but there's sort of a defacto standard in the HPC community to count one division as 4 flops.</p></li> <li><p>If a processor has a <strong>fused multiply-add</strong> instruction that does a multiplication and an addition in a single instruction -- generally A += B * C -- that counts as 2 operations.</p></li> <li><p>Always be careful in distinguishing between <strong>single-precision</strong> flops and <strong>double-precision flops</strong>. A processor that is capable of so many single-precision gigaflops may only be capable of a small fraction of that many double-precision gigaflops. The AMD Athlon and Phenom processors can generally do half as many double-precision flops as single precision. The ATI Firestream processors can generally do 1/5th as many double-precision flops as single precision. If someone is trying to sell you a processor or a software package and they just quote flops without saying which, you should call them on it.</p></li> <li><p>The terms megaflop, gigaflop, teraflop, etc. are in common use. These refer to factors of <strong>1000</strong>, <em>not 1024</em>. E.g., 1 megaflop = 1,000,000 flop/sec not 1,048,576. Just as with disk drive sizes, there is some confusion on this.</p></li> </ul>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload