January 11, 2011

Saten -- 1½ CPUs?

I was curious to see how much a certain task was loading the CPU in Saten, so I opened the task manager and left it running. And it had two CPU-loading diagrams, not one.

I didn't think this was a dual CPU. I did some looking, and found the explanation: it's an Atom Z540, and that processor supports hyperthreading. Evidently HP decided to use it.

So the "System Information" frame just shows the one CPU, but the task manager shows two CPU threads.

UPDATE: Hyperthreading was one of those ideas which didn't really pan out. The right approach was multiple cores, and that's how everyone's going now. But there's a generation of processors in there which still supports it, and I didn't expect it to show up in the Slate.

Posted by: Steven Den Beste in Computers at 11:13 PM | Comments (4) | Add Comment
Post contains 134 words, total size 1 kb.

1 Hyperthreading is back again, since it's actually useful in certain specific cases.  (The desktop not notably among them.)  The Atom, for example, is an in-order design with a long pipeline, so having a second hardware thread available to run while the main thread is stuck waiting on a memory access is a big advantage.

It's also good on servers where you have lots of threads to run.  Intel's server implementation of hyperthreading adds about 20% overall performance for about 5% more die area, which is a decent tradeoff.  Makes benchmarking hell, though, as single-threaded performance drops by about 40% when all the virtual CPUs are busy.  Sun's latest Niagara-3 processors, built to cope with the insanity of Java programmers, have eight threads per CPU and 16 CPUs per chip.

Posted by: Pixy Misa at January 12, 2011 01:49 AM (PiXy!)

2

All* the Intel 2010 cpus--the Core i3/5/7--are hyperthreaded as well as being dual or quad core.  My laptop, an i5, appears to be a quad-core CPU to Windows.

* I think there are one or two individual chips that don't, like a low-end quad i7.

Posted by: RickC at January 12, 2011 04:41 PM (uDU56)

3 The further the memory goes from CPU (measured in clocks), the more advantageous hyperthreading becomes. However, I hoped that the end of GHz race would reverse the trend as the DRAM controller implementations and basic DRAM technology catch up. However, it did not happen, at least so far.

Posted by: Pete Zaitcev at January 12, 2011 05:47 PM (9KseV)

4 Rick - it's actually much more confusing than that.  The i3 is dual-core dual-thread, the i5 is either dual-core dual thread or quad-core single thread, and the i7 has two, four or six cores with dual threads.  So four reported cores could be two real cores with hyperthreading or four without, depending on a single digit in the model designation.

Posted by: Pixy Misa at January 12, 2011 07:51 PM (PiXy!)

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