1 CPU, 2 Threads?

Y

Yaden

Gawd
Joined
Sep 30, 2005
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529
Here at work I've been going through some "new" computers that I recently received. I was puzzled by a CPU-Z result that showed the following:

Specification: Intel Pentium 4 CPU 2.8 GHz
Number of processors: 1
Number of cores: 1
Number of threads: 2 (max 2) per processor

Windows task manager shows two CPU windows as well but I've never seen 2 threads before in a CPU-Z report, whats this about?

FYI, am using CPU-Z 1.38.
 
I haven't looked at Intel procs in years, been buying AMD for myself. Most of our comps are fairly old and I never seen one with 1 proc, core and 2 threads. Thanks for the info though, glad it wasn't too much trouble. :rolleyes:
 
Those guys are harsh lol
Anyway, hyperthreading was just some stuff intel came up with to make their long pipelines not quite so innefficent. It helped make the chips perform quite a bit better and helped at multitasking.
 
Actually, IBM had 'HyperThreading' (which they simply call SMT, Simultaneous Multi Threading) before Intel did, if I'm not mistaken.
And this was on CPUs with 'short' pipelines.
Intel has also said that HyperThreading will return in 2008 or so, in one of the refresh-cycles of the Core2-architecture. So still with 'short' pipelines: http://vr-zone.com/?i=4322
 
It helps short pipelines too but I was under the impression that it helped the p4 so much because it was helpful at keeping that long pipeline busy.
 
Jakalwarrior said:
It helps short pipelines too but I was under the impression that it helped the p4 so much because it was helpful at keeping that long pipeline busy.
Click to expand...

it doesn't help shorten pipelines.... it re-prioritizes everything you do. If you're surfing the web and running a program, if you don't have the program truely running, the CPU will reallocate resources and move then to your web surfing. It reads as 2 threads because HT tricks the OS into believing there are 2 processors, when physically there is only 1.
 
It's a good idea, one that worked out pretty well.

But yeah... sounds like you've been out of the loop a bit ;)
 
StealthyFish said:
it doesn't help shorten pipelines.... it re-prioritizes everything you do. If you're surfing the web and running a program, if you don't have the program truely running, the CPU will reallocate resources and move then to your web surfing. It reads as 2 threads because HT tricks the OS into believing there are 2 processors, when physically there is only 1.
Click to expand...

You completely misread what Jakal wrote.
 
sounds like you've been out of the loop a bit
Click to expand...
For Intel, definitely. I took over this job back in the spring and wasn't paying much attention to Intel till then since my last (home) machines have been AMD based. I've never been shy to ask questions, plus I fully expected some smartass to speak up around here. Thanks again though, it sounds fairly interesting.
 
StealthyFish said:
huh. where do you work? That computer sounds a little old. a 2.8Ghz w/ HT?
Click to expand...

Anywhere that only requires it's employees to do some basic MS word work...

We were using P3's at my work lol.
 
Anywhere that only requires it's employees to do some basic MS word work...
Click to expand...
Exactly, don't need much for "office" and such apps. Plus my boss is cheap. ;)
 
Here's a bit of a primer on what Hyperthreading is all about.

CPU's since the orginal Pentium have been able to do two instruction at once. Once processing of an instruction has begun the CPU looks at the next instruction to see if it depends on the result of the currently executing one. If it doesn't the CPU will send it to the second pipeline for execution. Thus we get a performance boost. However, there are a lot of instruction that do depend on the currently executing one's results. In that case, the CPU has to stall that instruction until it can be executed. This mean that the second pipeline is left empty for the duration.

Hyperthreading takes advantage of the fact that the second pipeline is going to be empty quite a bit of the time. So when the CPU sees that the next instruction is going to be stalled, it'll look at another thread of instructions load them into the the second pipeline until the first thread's instruction aren't dependant on each other.

Hyperthreading however doesn't actually reprioritze any resources. It just looks at how it can keep all the execution units busy and not wasting time being idle. Once the original thread can use the resources it gets them back and the second thread will sit and wait it's turn just like it would have anyway.
 
Since Pentium Pro, you don't really have pipelines as such anymore...
You have 'execution ports' as Intel calls them. They are divided into several tasks, such as ALU (arithmetic logic unit), AGU (address generation unit), LSU (load/store unit), FPU (floating point unit, often also handles MMX/SSE).

What HyperThreading basically does is add a second core, up to the execution units.. So you get a second set of registers and logic to execute a stream of instructions. But the ports are shared with the first core (as are caches, FSB and such).

This way it acts like it's a two-core system, being able to process two streams of instructions at the same time (which means that an OS can run two threads/processes simultaneously). This works reasonably well because generally there will be idle execution ports in a single core.
 
Yaden said:
Here at work I've been going through some "new" computers that I recently received. I was puzzled by a CPU-Z result that showed the following:

Specification: Intel Pentium 4 CPU 2.8 GHz
Number of processors: 1
Number of cores: 1
Number of threads: 2 (max 2) per processor

Windows task manager shows two CPU windows as well but I've never seen 2 threads before in a CPU-Z report, whats this about?

FYI, am using CPU-Z 1.38.
Click to expand...

Called Hyperthreading, and its why I stuck with my Pentium 4 for while, even though A64 was faster in games, P4 with HT offered multi-tasking smoothness that wasn't available until the Pentium D & X2 series came out.

Its VERY old as the 3.06Ghz P4's came out like 4 years ago!

VERY Surprised you've neber hear of it!
 
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