Dual core confusion - dslreports.com

Author	All Replies
DrAsh join:2005-01-05 UK	Dual core confusion OK I'm a bit of a newb on this score - can someone clear this up for me. A 2GHz dual core has 2 cores each running at 2GHz, right?, so it can "do" app A at 2GHz and app B at 2 GHz (put really simplistically), but could it do just A at 4 GHz if needed, or is it really just a 2GHz machine that doesn't slow down as much as a single core when it's hammered by a bit of heavy multitasking? That is, 2 x 2 doesn't really equal 4 when it's a dual core (sorry for the unintended rhyme). Thx.
	to forum · permalink · · 2006-01-11 22:20:31 ·
rexbinary Mod King Premium join:2005-01-26 Plano, TX	The clock operates at 2GHz, so neither CPU will exceed that.
	to forum · permalink · · 2006-01-11 22:22:49 ·
Thinkdiff Premium,MVM join:2001-08-07 Bronx, NY	reply to DrAsh It's technically faster than 2 separate 2GHz processors. so yes, it can reach "4GHz" on some tasks.
	to forum · permalink · · 2006-01-11 22:23:03 ·
Thinkdiff Premium,MVM join:2001-08-07 Bronx, NY	reply to rexbinary said by rexbinary : The clock operates at 2GHz, so neither CPU will exceed that. Are you sure? I thought each core was rated for 2GHz..
	to forum · permalink · · 2006-01-11 22:23:37 ·
TearAbite join:2001-07-25 Rancho Cucamonga, CA ·Charter Pipeline	reply to DrAsh yes, yes, maybe, sorta, and..depends.. it will multitask better.. if the apps are writted to take advantage of 2 processors, it can ALMOST be like 2 seperate computers @2Ghz.. but.. there is a lot of overhead "thinking" in keeping the 2 cores from running into each other - so you'll never get a 2+2=4 .. suffice it to say, 2 is way better than 1 .. . -- Click HERE to see my FAKEz
	to forum · permalink · · 2006-01-11 22:24:14 ·
rexbinary Mod King Premium join:2005-01-26 Plano, TX ·Verizon FIOS	reply to Thinkdiff Well that's what I meant, neither core will operate over 2GHz. But the combined performance of both cores running at 2GHz would exceed the performance of a single 2GHz core, as you pointed out. -- Verizon FiOS 15/2 \| "Here's to the crazy ones. The misfits. The rebels." - Apple Computer \| FreeBSD & Novell SUSE Linux Fan \| Addicted to PvP \| EDIT: I seldom post without an edit.
	to forum · permalink · · 2006-01-11 22:26:06 ·
DrAsh join:2005-01-05 UK	reply to TearAbite Thanks guys, I get the overhead thing, so it does better than a single 2GHz but not as good as 2 x 2GHz - should have written "but could it do just A like a 4GHz single core if needed" instead of "but could it do just A at 4 GHz if needed", would have been clearer. So does MacOS X have the built-in capability to use (and control/administer) the resources of both cores for one app or process (forgive the woolly terminology I'm fast sinking out of my depth)? I'm thinking like a big computational job where both cores can do half of the job each, so that the net effect is as if the job was done on a faster than 2GHz single core machine. That's different from running two apps, each in a separate core isn't it? So does that kind of parallel speed improvement come "straight out of the box" with X for all apps if they demand that kind of grunt, or will it only be available for specially written programs - hence the differing performance claims, 2x and up to 5x, that I'm reading.
	to forum · permalink · · 2006-01-11 23:02:20 ·
metsfan489 METS - 2006 NL EAST join:2004-10-11 Oakland Gardens, NY clubs:	said by DrAsh : Thanks guys, I get the overhead thing, so it does better than a single 2GHz but not as good as 2 x 2GHz - should have written "but could it do just A like a 4GHz single core if needed" instead of "but could it do just A at 4 GHz if needed", would have been clearer. So does MacOS X have the built-in capability to use (and control/administer) the resources of both cores for one app or process (forgive the woolly terminology I'm fast sinking out of my depth)? I'm thinking like a big computational job where both cores can do half of the job each, so that the net effect is as if the job was done on a faster than 2GHz single core machine. That's different from running two apps, each in a separate core isn't it? So does that kind of parallel speed improvement come "straight out of the box" with X for all apps if they demand that kind of grunt, or will it only be available for specially written programs - hence the differing performance claims, 2x and up to 5x, that I'm reading. An application will only split a job across more than one core (or more than one processor) if the application was written to take advantage of more than one core/processor. When you write the application you are "threading it", or making it aware that it can do more than one job simultaniously. Now I believe that it is up to the Operating System to distribute the threads across the multiple cores/processors. (Could someone confirm or correct me about this)
	to forum · permalink · · 2006-01-11 23:10:47 ·
Thinkdiff Premium,MVM join:2001-08-07 Bronx, NY	reply to DrAsh OS X has complete support for SMP (Symmetrical Multi Processing) .. Unix relies on "threads" to send instructions to processors. if a program can utilize multiple threads (most do), then OS X will automatically distribute the threads across all available processors in the most efficient way possible. If you are running a single program, which is running a single calculation or string of calculations, it will most likely not utilize the full processor, but OS X will put that on one core, and place all the other less important instructions on the second core, optimizing the amount of processing power available to the most intensive applications.
	to forum · permalink · · 2006-01-11 23:13:11 ·
Thinkdiff Premium,MVM join:2001-08-07 Bronx, NY	reply to metsfan489 said by metsfan489 : Now I believe that it is up to the Operating System to distribute the threads across the multiple cores/processors. (Could someone confirm or correct me about this) Normally, yes. I believe it's specifically the kernel's job.
	to forum · permalink · · 2006-01-11 23:13:51 ·
DrAsh join:2005-01-05 UK	reply to Thinkdiff Right, so a dual core really is pretty much nearly twice as "good" as the same speed single core, for jobs with plenty of threads. My single calculation example would probably be a special case that regular users probably wouldn't come across very often. So looking at Safari at the moment I've got 9 threads (for just this one window I'm typing in), so Safari as a single app could be using all of both cores (except for the overhead), dividing up the threads. I could be viewing two different H.264 HD movies in two different windows simultaneously (can't think of a better, or more useful example at the moment, but that really smokes my 1GHz G4) Wow, that makes the new iMac seem pretty good value compared with the one you could buy just hours ago with the G5 in for the same cash. :):):):)
	to forum · permalink · · 2006-01-11 23:40:43 ·
cailyoung join:2003-06-30 Australia ·iiNet edit: January 12th, @12:36AM	said by DrAsh : Wow, that makes the new iMac seem pretty good value compared with the one you could buy just hours ago with the G5 in for the same cash. :):):):) Shutupshutupshutupshutup ;P
	to forum · permalink · · 2006-01-12 00:36:09 ·
Hot_Rats He's Not Tor Johnson join:2003-07-08 Indianapolis, IN clubs:	reply to DrAsh Multiple cores will be faster for multi-threaded applictions and in general will allow the OS to remain responsive when a single thread is stuck or executing at high priority and maxing out one of the cores. There are a few situations where a single fast core is better (gaming, dedicated rendering or processing i.e. "start the render and go to lunch") but overall if the computer is used by someone who does more than one thing at once, more cores are better. Even single-threaded renders can be helped by multiple cores if they are I/O intensive, because the I/O is going to require some CPU time as well. -- "I'm downloading with a 56k modem. Can you give me step by step instructions on how to install x86 Solaris?? Please reply back. Thanks."
	to forum · permalink · · 2006-01-12 08:39:23 ·
DrAsh join:2005-01-05 UK	So you could argue that going to multiple cores/processors with an OS like X is actually desirable in its own right rather than being just a way around a currently insurmountable problem - not being able to speed chips up any faster. I was under the impression the dual core thing was just a sub-optimal botch to get around the fact that the PC chip makers seem to have been hitting a brick wall trying to make faster single cored chips (and deflect some of the criticism). Thanks for the info guys - guess I'll have to start saving for a rev B iMac
	to forum · permalink · · 2006-01-12 10:59:06 ·
dennismurphy Put me on hold? I'll put YOU on hold Premium join:2002-11-19 Parsippany, NJ ·Optimum Online	said by DrAsh : So you could argue that going to multiple cores/processors with an OS like X is actually desirable in its own right rather than being just a way around a currently insurmountable problem - not being able to speed chips up any faster. I was under the impression the dual core thing was just a sub-optimal botch to get around the fact that the PC chip makers seem to have been hitting a brick wall trying to make faster single cored chips (and deflect some of the criticism). Thanks for the info guys - guess I'll have to start saving for a rev B iMac No way --- multi-core and multi-processor system have many scaling advantages versus a single-CPU system. Just ask Sun!
	to forum · permalink · · 2006-01-12 11:24:01 ·
Hot_Rats He's Not Tor Johnson join:2003-07-08 Indianapolis, IN clubs:	reply to DrAsh It is true that the dual cores are kind of a workaround solution to the issue of increasing the processing power of the core. I have been in love with dual CPU systems since the late 90's or so when I worked on multiprocessor PC workstations. They were so responsive, there's the whole "Well x is taking a while to open, so I might as well go back to y and do something else" and you actually could without it being annoyingly slow. So regardless of it being a "hack" or "workaround" it does have some neat side benefits most home-users will take advantage of, even without running multi-threaded 3D rendering applications. Hopefully, this trend will mean further optomization of the ability to get the most out of the "extra" core(s) and more programs being written to take advantage of the extra core if available. -- "I'm downloading with a 56k modem. Can you give me step by step instructions on how to install x86 Solaris?? Please reply back. Thanks."
	to forum · permalink · · 2006-01-12 11:26:56 ·
tokevino Rain join:2001-12-03 AZ edit: January 12th, @12:10PM	reply to DrAsh said by DrAsh : Thanks guys, I get the overhead thing, so it does better than a single 2GHz but not as good as 2 x 2GHz No, I don't think you get it. There is no big difference between multi-core and multi-processor. Both of them will result in some kind of overhead. As about this "2x2" issue: Two is better than one, mostly, but rarely, you still see some single threaded apps doing better on a single core for some reason, (given the same clock, of course). Is two cores better or worse than two separate processors? Not necessarily one way or the other, it all depends on design and engineering. You can get some objective comparison from anandtech.com. Like how Intel's Core Duo runs against AMD's x2s, or how x2s or Pentium Ds run against single cores. Oh, one thing that might not be good news: I recall Photoshop and Mozilla/Firefox were some of the apps that run better on a single core, given the same clock speed, (with Windows and PC at this time). Let's hope OS X can make these apps run better on x86 based duals. Of course, you can always assign one app on one core/processor and do the rest on the other.
	to forum · permalink · · 2006-01-12 12:07:00 ·
DrAsh join:2005-01-05 UK	reply to dennismurphy said by dennismurphy : Just ask Sun! Wow, 32 threads at 1.2 GHz each - might be overkill for surfing the web, but I sure would like to try it Does Steve know about these?
	to forum · permalink · · 2006-01-12 12:07:22 ·
Johnny Premium join:2001-06-27 Atlanta, GA	reply to DrAsh Let us not forget that in defense of systems like the dual processor 2 gHz G5, each processor has its own independent frontside bus running at 1 gHz. The Core Duo shares its 667 mHz bus between the two cores. Of course, almost no apps saturate either of these buses at these speeds, so it is a theoretical advantage - but look at the streaming benchmark on the Core Duo versus the G4 - 667 versus 167 bus speed, and almost 6x the performance. -- »homepage.mac.com/johnnylundy/Fil···g27.html
	to forum · permalink · · 2006-01-12 12:34:55 ·
DrAsh join:2005-01-05 UK	reply to tokevino said by tokevino : No, I don't think you get it. There is no big difference between multi-core and multi-processor. Both of them will result in some kind of overhead. Sorry, my sloppy terminology seems to be causing some mis-aprehension. What I was trying to question is whether a dual core 2GHz is as good as a single core 4GHz. I thought the dual cores were a botch because they couldn't make the 4GHz, but now it seems for the kind of stuff most people do, the dual core 2GHz is actually more preferable (even with the overhead involved with having 2 cores). I don't know how dual cores compare with dual processors, but it seems they aught to be better as well.
	to forum · permalink · · 2006-01-12 12:49:40 ·


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