Question Why don't CPUs have an odd number of cores ?

FlameTail

Member
Dec 15, 2021
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There are 2,4,6,8,10,12,14...32..128 core CPUs. But all these are EVEN numbers. CPUs with odd-number of cores are almost non-existent. WHY ?

1. Making an actual CPU die with an odd number of cores.

In this scenario, I know the answer to the question.

It's possible to actually make a die with an odd number of physical cores. However this is challenging, because having an odd number of cores kills the symmetry and makes designing the CPU really complicated.

The Xenon ( not Intel Xeon ) processor is a rare example with 3 actual cores physically present in the die.

https://www.quora.com/Why-do-CPUs-always-have-an-even-number-of-cores-4-6-8-etc -Quora: Why do CPUs always have an even number of cores (4, 6, 8, etc.)?

2. Binning a CPU with even-number of cores to get an odd-number of cores.

Example:

An AMD Zen 3 CCD has 8 cores. If one core is defective, AMD can disable that core and sell it as 7 core CPU. However they do not do so. Instead they will probably disable 2 cores and sell it as 6 core CPU. WHY?

(a) Is there any physical/technical/software/hardware limitation that prevents them from doing this ?

(b) If NOT, what is the reason binned CPUs don't have an odd number of cores ?

The Phenom processors used to have a Triple-Core variant, which was basically obtained by disabling one core of a 4-core die. Nonetheless, we haven't seen such a CPU in recent years.

So (a) and (b) are my actual questions and i am looking forward to an answer to these.
 

Tuna-Fish

Golden Member
Mar 4, 2011
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For (a), AMD did have such a constraint for Zen 1 and Zen 2, because every core complex had to either have 0 cores or the same amount of cores as all the other ones that had any. With two 4-core CCX this meant that if you have one faulty core, you have to either competely disable the CCX containing it, or disable one core out of both CCX. Then if you had 2 faulty cores in the same CCX, it meant that either you wholly disabled that CCX, for a 4-core, or you disabled 2 cores out of both CCX:es, for a 4-core. Then a 3-core would have been possible if you are completely disabling one CCX and disabling one core of the remaining one, but that would require ~3 independent faults in a single chip which would be really uncommon.

With Zen3, they could probably ship a large portion of the 5600:s as 7-cores. Most likely the choice to make them 6-cores instead is mostly marketing-related: they want to keep the SKU amounts reasonable, and to keep them sufficiently distinct from each other.
 

Abwx

Diamond Member
Apr 2, 2011
9,473
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It still exist , and brand new...

The Intel Pentium 8500 is an entry-level low-power mobile CPU for thin and light laptops based on the Alder Lake architecture. It was announced in early 2022 and offers one performance core (P-cores, Golden Cove architecture) and 4 efficient cores

 
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mikeymikec

Lifer
May 19, 2011
15,239
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There are 2,4,6,8,10,12,14...32..128 core CPUs. But all these are EVEN numbers. CPUs with odd-number of cores are almost non-existent. WHY ?

1. Making an actual CPU die with an odd number of cores.

In this scenario, I know the answer to the question.

It's possible to actually make a die with an odd number of physical cores. However this is challenging, because having an odd number of cores kills the symmetry and makes designing the CPU really complicated.

The Xenon ( not Intel Xeon ) processor is a rare example with 3 actual cores physically present in the die.

https://www.quora.com/Why-do-CPUs-always-have-an-even-number-of-cores-4-6-8-etc -Quora: Why do CPUs always have an even number of cores (4, 6, 8, etc.)?

2. Binning a CPU with even-number of cores to get an odd-number of cores.

Example:

An AMD Zen 3 CCD has 8 cores. If one core is defective, AMD can disable that core and sell it as 7 core CPU. However they do not do so. Instead they will probably disable 2 cores and sell it as 6 core CPU. WHY?

(a) Is there any physical/technical/software/hardware limitation that prevents them from doing this ?

(b) If NOT, what is the reason binned CPUs don't have an odd number of cores ?

The Phenom processors used to have a Triple-Core variant, which was basically obtained by disabling one core of a 4-core die. Nonetheless, we haven't seen such a CPU in recent years.

So (a) and (b) are my actual questions and i am looking forward to an answer to these.
Given the two-state nature of the bit, it's not surprising that even numbers are more commonly embraced in computing. It's more of a question about what humans find aesthetically pleasing.
 
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FlameTail

Member
Dec 15, 2021
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Given the two-state nature of the bit, it's not surprising that even numbers are more commonly embraced in computing. It's more of a question about what humans find aesthetically pleasing.
In that case if someone made a 69-core CPU, it would sell faster than Tesla's (ludicrous) Cyberwhistle
 

Doug S

Golden Member
Feb 8, 2020
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Apple A8X had three (big, since they didn't have any little back then) CPU cores.

The A15 has five GPU cores (all five enabled in the "Pro" phones, four enabled in the non Pro)
 
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VirtualLarry

No Lifer
Aug 25, 2001
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My most recent router purchase was a triple-core. Not x86 family, but odd-numbered core products are out there, and being advertised.
 

desrever

Junior Member
Nov 6, 2021
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It just make sense to make things that are even rather than odd, people are psychologically more drawn to even numbers. They want things that are even. Just think of arbitrary things like model names for GPUs, they could name them anything they want but they basically always choose round even number. People tend to think a round even number is more than it is and think a odd number as less. When people pay, the price is usually something like 999.99 or 999.97 cause they think it is less. When people get something, the thing they buy is usually the "CPU 1000" because they think it's better.

Also from an engineering point of view, if you want to scale up anything, logical way to do it is to double it. So if you have 1 core (odd), the next improvement is 2 cores (even) and will be even no matter how many times you double it. Even if you started with 3 cores, you want to scale up to double it will be 6 (even again).
 

Hotrod2go

Member
Nov 17, 2021
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It's really triple-module. Not exactly the same thing.
So a module is a core is it? this website we are on reported the legal outcome of this argument right here
although that story was with FX8000 & 9000 series, the principal of modules being interpreted as cores applies across the whole range of FX series CPU.
That's why my earlier post was setting aside arguments about how a core is defined.
 

NTMBK

Diamond Member
Nov 14, 2011
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Arguments aside for what defines a core, but AMD's FX-6xxx series could be interpreted as triple core.
But that's still a four-module die with one module disabled- not built from the ground up as a triple core.

Stoney Bridge is a single core/module, so I guess that would count?
 

DrMrLordX

Lifer
Apr 27, 2000
19,151
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So a module is a core is it?
The term "module" exists to describe a design that really doesn't have cores in the traditional sense. In integer workloads, it's like 2c, but in fp workloads, it's like 1c - unless you use XOP then maybe it's more like 2c? You see the issue here? It's not worth it to ask the question, "how many cores does a CON CPU have?" because the answer is rarely satisfactory.

CON CPUs have modules, end of story.
 

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