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I've been reading What Every Programmer Should Know About Memory by U. Drepper, where they state the following on p. 3:

Red Hat, as of 2007, expects that for future products, the “standard building blocks” for most data centers will be a computer with up to four sockets, each filled with a quad core CPU that, in the case of Intel CPUs, will be hyper-threaded.2 This means the standard system in the data center will have up to 64 virtual processors.


2 Hyper-threading enables a single processor core to be used for two or more concurrent executions with just a little extra hardware.

What I'm unclear about is how such a system would have 64 (virtual) processors.

Let us even assume that a hyper-threaded CPU consists of 2 processors (I've read about this technology, so I know that it may even perform worse, and at most about 30% faster than a non-hyper-threaded CPU). A quad-core consists of 4 processors, so a device with 4 hyper-threaded quad-core CPUs would have 4 * 2 * 4 = 32 processors.

What am I missing?

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The statement doesn't contain any reference to the number of cores per CPU.

64 virtual processors / 4 sockets / 2 (HT) would mean that each CPU would have to have 8 cores. 2008 just a year after the date mentioned in that excert there were already 6 core CPUs available. The write probably though that later on 8 cores (at least) would be doable.

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    Sure does, "each filled with a quad core CPU"? Do you think the last sentence there (before the footnote) refers to a different kind of system? – J. C. Dec 18 '19 at 13:53
  • Indeed that's odd but probably simply something that slipped by or another extrapolation based on having HT (yes the footnote wouldn't fit). As far as I know there have been rumors about AMD working on HT with up to four threads. – Seth Dec 18 '19 at 13:55
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    The statement by Red Hat was a prediction made in 2007. I mean the footnote is incorrect, due to the fact, there are no processors with hyper-threading that exceed 2 threads per core even in 2019. In fact based on the current leaks we any product in 2020 that can do more than 2 threads per core. – Ramhound Dec 18 '19 at 15:10
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    It seems IBM POWER8 processors have up to 8 threads per core - see this anandtech article – lx07 Dec 18 '19 at 18:57

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