- Joined
- Mar 17, 2007
- Messages
- 9,311
I understand, what HT is, but i do not understand, what advantage it gives.
4 Cores * 2 Ghz or 8 Cores * 1 Ghz...sorry, i don't understand the benefit of the second option.
Hail's analogy is fairly good; it's important to note that in that analogy, the CPU (not the OS - this is lower-level than the OS) can pump water from both aqueducts at the same time. You can apply the same concept with more than two "aqueducts", and companies such as IBM and Sun Microsystems have done this. This technique in general is called "simultaneous multithreading" or SMT; hyperthreading is just Intel's marketing word for it.
And while having two actual CPU cores (like Core 2 Duo or Pentium D gives you) is better in terms of performance, it is not necessarily better in terms of chip area, which in turn affects chip cost. Hyperthreading averages 15-25% performance improvement when a program supports multiple threads (Intel cites 25% in their paper on the Pentium 4 with hyperthreading), but increases chip area by less than 5% (source). Adding a second core will approximately double performance (slightly less than 100% improvement), but will double chip area, and thus at least double the cost for the raw materials (likely more in practice). So it's not just marketing. The improvements may not be drastic, and yes, it is possible for it to decrease performance slightly, but there are good, technically sound, reasons to implement hyperthreading.
Adding hyperthreading to a computer with 4 cores at 2 GHz doesn't equate it to 8 cores at 1 GHz. Basically, if you're running a program that can take advantage of anywhere from 1 through 4 cores, you won't notice much if any difference. If you're running a program that could take advantage of 8 cores, you'll probably get a 15-25% performance boost. Key to why this is different than 8 cores at 1 GHz is if you consider a program that uses 1 thread, such as Civ4. On your 4-core, 2 GHz machine with hyperthreading, Civ4 will use 1 core at 2 GHz, with no benefit from the hyperthreading. On an 8-core, 1 GHz machine, Civ4 will use 1 core at 1 GHz - all else equal, it will run at half the speed as your 4-core machine with hyperthreading. Windows may show 8 "cores" in Task Manager, but you aren't getting half the speed per core with hyperthreading than without it.
If you're interested in more details, send me a PM. It's hard to say what crucial details I might be leaving out without knowing how much of a technical background you have, and I can't read German, so your earlier link doesn't help me.
Still planning to have two cores (without hyperthreading) whenever Civ5 comes out myself. Don't have the means to upgrade without the need to at this time, and my 2.7-year-old laptop doesn't feel that old, anyways.