How many ALUs are in a CPU?

cpu alu
Duffman picture Duffman · Mar 15, 2015 · Viewed 9.6k times · Source

I believe that there is "1" ALU per core in a CPU correct? I seem to be having a little bit of difficulty looking this up. Someone asked me in a discussion for school so I am quite curious as well.

Answer

osgx picture osgx · Mar 15, 2015

Modern superscalar (http://en.wikipedia.org/wiki/Superscalar) CPU has many execution pipelines, and there can be ALU in several pipelines. For example, Intel *Bridge microarchitecture has 6 execution ports; and some ports has 2 or 3 execution pipelines behind them; Haswell has 8 ports. Check http://www.anandtech.com/show/6355/intels-haswell-architecture/8 - it has picture of pipelines for Nehalem, Sandy Bridge and Haswell with some ALU marked (I count 6 ALU for Haswell; and there are many smaller ALUs in this billion sea of transistors)

There are also SIMD ALU common in current days (SSE2, AVX, ...); SIMD has several ALU to work on short vector.

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