SMT vs. Hyperthreading (What's the difference?)

[USAG_Techie]

I was watching the "Use your Gaming PC's Extra Power as a NAS Ultimate Guide" video and Linus brought up the "hyperthreading" term when explaining what CPU you would need for a desktop/NAS that supports virtualization. Now I was searching about the interwebs and was seeing that Intel uses this technique whereas AMD uses SMT technology. Can anyone give me a clear description between the two if there are any differences or if they are similar?

[Overl0rd]

HyperThreading is Intel's brand name for SMT (simultaneous multithreading). Both boil down to the same principle, but Intel and AMD have their own implementation.

[LukeSavenije]

nothing

 

it's the same

 

two hands for one mouth

[TeaDrinkingMaximus]

Well technically IBM has their own implementation also and was used in the XBOX 360. 3 cores, 6 threads.

[USAG_Techie]

2 minutes ago, TeaDrinkingMaximus said:

Well technically IBM has their own implementation also and was used in the XBOX 360. 3 cores, 6 threads.

I never knew that... Hm.

[LukeSavenije]

3 minutes ago, TeaDrinkingMaximus said:

Well technically IBM has their own implementation also and was used in the XBOX 360. 3 cores, 6 threads.

ibm? do they still make cpus these days? i thought xb used amd jaguar?

[TeaDrinkingMaximus]

Just now, LukeSavenije said:

ibm? do they still make cpus these days? i thought xb used amd jaguar?

Just memorabilia at this point, but worth a mention.

[Meticulous]

On 3/17/2019 at 7:56 PM, LukeSavenije said:

ibm? do they still make cpus these days? i thought xb used amd jaguar?

Yeah, they do. Check out Power10. IBM makes PowerPC CPUs these days. I'm not sure who's buying them, but it would seem like some folks are. I know there's a company called Raptor Engineering which makes PCs and servers using IBM's Power10 CPUs. I don't own one of their systems, but I know about them from my days of keeping tabs on the FSF.

[Sarra]

3 year thread bump...

 

Wasn't there an implementation that had 1 core 4 threads?

[RandomStyuf]

IBM and Sun (back in the day, not sure if Oracle continued with it) had wider SMT processors in their PowerPC and SPARC architecture lines. 

I'm pretty sure it went up to 8 threads per core for at least one of them, but I don't remember for sure. (It's possible they even went up to 16 threads but my memory could be playing tricks on me). The thing is, such wide SMT is useful in some tasks but can require engineering tradeoffs that make the CPU worse in other tasks.

 

On a very technical note, I'm not 100% sure if the SPARC implementation was actually SMT or a multiplexing (sometimes called "Fine Grained") in-order engine implementation. The point is, not all cores that run multiple threads on a single core are actually SMT, but back to the point, the Intel and AMD implementations are both similar and do SMT execution.