Question about CPUs (4 vs 8 core)

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Gizmo j

Gizmo j

Golden Member
Nov 9, 2013
1,469
407
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A guy named "Sangeet Khatri" said just because a CPU has twice as many cores does not equal twice amount of power.


So I looked up the benchmarks of the FX4350 and FX8350, there both the same CPU except one has 4 cores and the other has 8 cores.

On cpubenchmark.net fx4350=5231 and fx8350=9078

Meaning the difference between the two is 73.5%

My question, is it a similar amount of performance increase in other CPUs with similar specs?
 
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BallaTheFeared

Diamond Member
Nov 15, 2010
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I think what he meant is that just because the 8350 has twice the cores as the i5 it doesn't mean it's twice as fast.

On the contrary the 8350 is similar in tasks that use 8 cores, but considerably slower in tasks that use 4 or less.
 
Gryz

Gryz

Golden Member
Aug 28, 2010
1,551
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It depends.

- When I impregnate 9 different women, will I get a baby in 1 month ? Nope. Some things can not be parallelized. The same is true of some algorithms. For some problems, you can not write programs that make use of a 2nd, or 3rd core. Those programs will run just as fast on a CPU with 1 core, as on a CPU with multiple cores.

- Sometimes algorithms can be created to run in parallel on multiple cores. But the software developer has not done that yet. If you think of a particular program that you are concerned about, you need to check if it can make use of multiple cores or not.

- How fast does each core run ? CPUs run at a particular "frequency". An internal "clock" ticks once, or a few times per nanosecond. Every time that clock ticks, the CPU performs a step in a computation. The faster the clock, the faster the CPU does its computations.

- How effective does a core run ? During each clock-tick, a CPU does a little part of work. Some CPUs can do a little bit more work during once clock-tick, than other CPUs. This can make one CPU a little (5-50%) faster than another CPU that runs at the exact same frequency. (This is called IPC, = Instructions Per Cycle).

- And then there are more details. Cache. Bus-speed. Memory-speed. Etc. Many small improvements on the overall architecture that can allow the CPU to keep running more efficiently. The result will be that some programs will run faster. Again, if you want to know how a specific program will behave, it is best to (read a) benchmark (about) that specific program.

- Are all the cores really full blown cores ? Intel has hyper-threading. That means that an 8-core CPU has 4 real cores, and 4 extra virtual cores. The virtual cores do make some programs (10-40%) faster compared to just 4 cores. But not for all software. AMD has a different architecture, when there are 8 cores, but only 4 FPUs (floating point units). So if you run a program that does mostly integer-computations, an AMD 8-core CPU can be twice as fast as a 4-core CPU. But if your program does mostly floating-point computations, then an 8-core CPU might be just as fast as a 4-core.

So lots of details to be aware of. On average an 8-core will be faster than a 4-core. But not always. And sometimes the 4-core might even be faster. The smartest thing to do is: check benchmarks of your favorite programs (and favorite games), and base your decision on that info.
 
TuxDave

TuxDave

Lifer
Oct 8, 2002
10,571
3
71
Gryz said:
It depends.

- When I impregnate 9 different women, will I get a baby in 1 month ? Nope. Some things can not be parallelized. The same is true of some algorithms. For some problems, you can not write programs that make use of a 2nd, or 3rd core. Those programs will run just as fast on a CPU with 1 core, as on a CPU with multiple cores.
Click to expand...

I was in the middle of trying to write up a "non-CPU" analogy for non-parallel tasks. But I think nothing trumps this one. :p
 
S

Sable

Golden Member
Jan 7, 2006
1,130
105
106
Gryz said:
It depends.

- When I impregnate 9 different women, will I get a baby in 1 month ? Nope. Some things can not be parallelized. The same is true of some algorithms. For some problems, you can not write programs that make use of a 2nd, or 3rd core. Those programs will run just as fast on a CPU with 1 core, as on a CPU with multiple cores.
Click to expand...

LOL.
 
sm625

sm625

Diamond Member
May 6, 2011
8,172
137
106
It's more than that. On my rather slow dual core non HT machine, I can do one instance of super pi 1M in 17 seconds. You would think I could run two different instances (different copies from different folders) also in 17 seconds, but it actually takes 21 seconds to run two. Can you guess how long it takes to run 3? 31 seconds. One reason is because they all share the same cache. I'm pretty sure the entire program, all 3 instances all fit in cache, but each process must be getting stuck waiting. For much the same reason, the 8 core cannot run even a perfectly multithreaded benchmark twice as fast vs a 4 core.
 
blastingcap

blastingcap

Diamond Member
Sep 16, 2010
6,654
5
76
Gryz said:
It depends.

- When I impregnate 9 different women, will I get a baby in 1 month ? Nope. Some things can not be parallelized. The same is true of some algorithms.
Click to expand...

Nice explanation. Lol. :D :thumbsup:

sm625 said:
It's more than that. On my rather slow dual core non HT machine, I can do one instance of super pi 1M in 17 seconds. You would think I could run two different instances (different copies from different folders) also in 17 seconds, but it actually takes 21 seconds to run two. Can you guess how long it takes to run 3? 31 seconds. One reason is because they all share the same cache. I'm pretty sure the entire program, all 3 instances all fit in cache, but each process must be getting stuck waiting. For much the same reason, the 8 core cannot run even a perfectly multithreaded benchmark twice as fast vs a 4 core.
Click to expand...

Infighting among the pregnant women eating from the same limited food supply?
 
podspi

podspi

Golden Member
Jan 11, 2011
1,982
102
106
Gryz said:
It depends.

- When I impregnate 9 different women, will I get a baby in 1 month ? Nope. Some things can not be parallelized. The same is true of some algorithms. For some problems, you can not write programs that make use of a 2nd, or 3rd core. Those programs will run just as fast on a CPU with 1 core, as on a CPU with multiple cores.
Click to expand...

:thumbsup:

Though after 9 months, your err, "production rate" of babies will be 1 a month. :colbert:
 
H

hackmole

Senior member
Dec 17, 2000
250
3
81
If anyone hasn't done video rendering and editing then they haven't used the full benefit of a computer because videos is a huge thing in life especially now that most cameras and even cell phones do videos as well. The problem is that video rendering which you absolutely need to do when you create videos takes a tremendous amount of computer time. Video software is capable of dividing up the work between the processors. That means an 8 core will do the rendering twice as fast as a 4 core and maybe even faster if the 8 cores are slightly faster chips. Time in getting things done is very important and so yes it would definitely be worth getting an 8 core for video rendering which I don't see how anyone can get along without doing at some point or another.
Yes, it doesn't make a damn bit of difference for word processing but anyone who uses a computer will at some point want to do a lot more than that like video rendering of personal videos, converting movies to DVD, converting DVD movies to computer movies and so on. These have been very important things to me and I can't wait for next years Haswell 8 core or whatever it is called.
 
Virgorising

Virgorising

Diamond Member
Apr 9, 2013
4,470
0
0
Gryz said:
It depends.

- When I impregnate 9 different women, will I get a baby in 1 month ? Nope. Some things can not be parallelized. The same is true of some algorithms. For some problems, you can not write programs that make use of a 2nd, or 3rd core. Those programs will run just as fast on a CPU with 1 core, as on a CPU with multiple cores.

- Sometimes algorithms can be created to run in parallel on multiple cores. But the software developer has not done that yet. If you think of a particular program that you are concerned about, you need to check if it can make use of multiple cores or not.


- How fast does each core run ? CPUs run at a particular "frequency". An internal "clock" ticks once, or a few times per nanosecond. Every time that clock ticks, the CPU performs a step in a computation. The faster the clock, the faster the CPU does its computations.

- How effective does a core run ? During each clock-tick, a CPU does a little part of work. Some CPUs can do a little bit more work during once clock-tick, than other CPUs. This can make one CPU a little (5-50%) faster than another CPU that runs at the exact same frequency. (This is called IPC, = Instructions Per Cycle).

- And then there are more details. Cache. Bus-speed. Memory-speed. Etc. Many small improvements on the overall architecture that can allow the CPU to keep running more efficiently. The result will be that some programs will run faster. Again, if you want to know how a specific program will behave, it is best to (read a) benchmark (about) that specific program.

- Are all the cores really full blown cores ? Intel has hyper-threading. That means that an 8-core CPU has 4 real cores, and 4 extra virtual cores. The virtual cores do make some programs (10-40%) faster compared to just 4 cores. But not for all software. AMD has a different architecture, when there are 8 cores, but only 4 FPUs (floating point units). So if you run a program that does mostly integer-computations, an AMD 8-core CPU can be twice as fast as a 4-core CPU. But if your program does mostly floating-point computations, then an 8-core CPU might be just as fast as a 4-core.

So lots of details to be aware of. On average an 8-core will be faster than a 4-core. But not always. And sometimes the 4-core might even be faster. The smartest thing to do is: check benchmarks of your favorite programs (and favorite games), and base your decision on that info.
Click to expand...


Brilliant delineation. Cept for the startling initial analogy re impregnating 9 women which was VERY Eeeeeewwww.:thumbsdown: But not quite AS Eeewww as any female not in charge of her own reproductive everything.

Good analogy too in response: given how many programs (still the majority) are written for 32-bit, can't expect any improvement in running those if you are running a 64-bit OS, tho many people expect just that.
 
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P

ph2000

Member
May 23, 2012
77
0
61
Gryz said:
It depends.

- When I impregnate 9 different women, will I get a baby in 1 month ? Nope. Some things can not be parallelized. The same is true of some algorithms. For some problems, you can not write programs that make use of a 2nd, or 3rd core. Those programs will run just as fast on a CPU with 1 core, as on a CPU with multiple cores.
Click to expand...

not quite fit analogy i think
since you will get 9 baby from the same time frame
instead of 9 year :\
 
JEDIYoda

JEDIYoda

Lifer
Jul 13, 2005
33,986
3,321
126
Gryz said:
It depends.

- When I impregnate 9 different women, will I get a baby in 1 month ? Nope. Some things can not be parallelized. The same is true of some algorithms. For some problems, you can not write programs that make use of a 2nd, or 3rd core. Those programs will run just as fast on a CPU with 1 core, as on a CPU with multiple cores.
Click to expand...
changed for the sake of accuracy -- If I could impregnate 9 different women,....
 
Gryz

Gryz

Golden Member
Aug 28, 2010
1,551
204
106
Virgorising said:
Good analogy too in response: given how many programs (still the majority) are written for 32-bit, can't expect any improvement in running those if you are running a 64-bit OS, tho many people expect just that.
Click to expand...

I can't agree.

With a 32-bit OS, you can address at most 2^32 bytes. Total. All programs together. Plus the OS itself (kernel, drivers, buffers, etc). So even though Virtual Memory is 4GB, the actual amount of RAM that can be used is less. Under Windows it's something like 3.2GB. If you have a browser open, another program can use 0.5GB less. Etc, etc.

If you run a 64-bit OS, the situation changes. The OS (kernel, drivers) still needs some RAM. You still lose memory because of overhead (buffers). But each 32-bit process now can have 3.2GB of RAM, without bothering other processes. Have your browser open with lots of tabs, it doesn't matter if it uses a GB of RAM. Run some more programs in the background, that use RAM. Your 32-bit applications can still use 3.2GB each. Even if you run out of RAM, although less likely with a few 32-bit applications and 6GB of RAM, the OS can just use the page-file.

So yes, running a 64-bit OS with 32-bit applications really can make a difference.
 
Gryz

Gryz

Golden Member
Aug 28, 2010
1,551
204
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I'm surprised that people laugh about my analogy. Haven't you heard that one before ? I didn't come up with it. I've must have heard it at least 10 years ago.

I still think it's the best example to explain that there are things that can not be parallelized. Try to come up with a better example, I challenge you ! :) There are none. Maybe I should have used a different word than "impregnate". English is not my first language. Saying "knock up" sounds even worse. What would be the correct word to use ?
 
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