Why is it that CPUs always have even numbers of cores?

[xXCrossfireXx]

So I've been looking at CPUs for a while, and I've noticed something: All CPUs have even numbers of cores (unless it's single core, but that doesn't count). I mean I've seen 2 core, 4 core, 6 core, 8 core, 12 core, and 18 core, but I've never seen anything like 3 core, 5 core, 7 core, or 9 core. Can someone tell me why this is?

 

[Deleted member 217926]

https://en.wikipedia.org/wiki/Athlon_II

 

[Dugimodo]

Because that's how manufacturers choose to make them. AMD does have some 3 core CPU's but they are actually quad cores with one core disabled so it doesn't really count.

 

[MrKrako]

I guess because at some point it was decided to use two cores in the same system. After that, all was easy because adding more cores mean "just duplicate it". It is not that simple, but i don't think any other reason apart from that a the layout requirements. Adding third core parties would translate in changing how the cores are arranged and would leave a space unused (due to the processor being rectangular). I mean, you can use a rectangular space to fit even number of cores but 3 or 5 cores would leave to many wasted space.

Normally those 3 cores processor from AMD were 4-core processor with one of them disabled because it was faulty.

 

[photonboy]

HT is another reason.

Intel can make three processors like THIS in order of increasing performance (depending on the task):

1) 2-core
2) 2-core + HT
3) 4-core

I'm not sure adding a 3-core would add much to the lineup.

Actually, it COULD be a very good choice, especially for a future AMD APU. They could have a 3-core + HT, then utilize the extra space for the GPU. So it might be the best balance for gaming.

For INTEL I mean in terms of PROFIT. I'm sure someone simply figured out 3-core CPU's didn't make sense in terms of overall profit.

 

[Deleted member 217926]

Because that's how manufacturers choose to make them. AMD does have some 3 core CPU's but they are actually quad cores with one core disabled so it doesn't really count.

Those 3 core Athlon II chips were originally marketed because not all silicon is created equally. A chip that comes off the production line perfectly would have been a Phenom II. But you will have errors for one reason or another and if a single core failed testing but the other 3 were fine it was sold as an X3. The X3 proved so popular that AMD started making them on purpose though by starting with a full Phenom II and disabling the cache and a core. That's why some X3s unlock into a full Phenom and others won't. It just depends on if you got a damaged or a purposefully disabled chip. To be fair some chips that didn't pass testing would still unlock but it was luck of the draw.

 

[Delroy Monjo]

It's a binary environment.

 

[synphul]

Before dual/quad/hex core etc there were single core cpu's from both camps.

 

[gamerk316]

From a design standpoint, it's easier to put together a dual core system, then replicate. Bulldozer contained two cores per module, which is why every BD derived chip has cores in multiples of two; it was literally designed around two cores = one module. For Intel, you have HTT which basically mandates even core count. Odd core designs are simply wasteful.