Question Why dont we have odd numbers of cores ?

Mrgr74

Commendable
Just curious ,

Why no one is making CPUs with odd numbers of cores ? like 3 ,5 7 ,9 , 15 , 31cores?
Hi @nofanneeded

AMD did with their Tri core CPU's. As with any CPU really, but in years past, AMD was known for some of their CPU's having some of their cores locked, namely their earlier unlocked "Black Edition" (Tho those CPU's weren't only known for this) CPU's being able to be unlocked if paired with the correct motherboard and a healthy dose of luck.

Such as the AMD dual Core 7750 BE. There were a TON of people that were able to "unlock" an additional 2 cores on this particular CPU. Sadly while I still have my 7750 BE (and it still works) I was unable to get the additional 2 cores to run stable and so kept it "locked" at the stock 2. I remember I spent BANK on the mobo as well. I remember I drove 90 minutes to pick it up at a Fry's in another city. The name of it eludes me but I have it as well locked away in storage.

As for other odd # of CPU's, they are out there. I would hazard a guess that they are not a good overall use of silicone during the manufacturing process. If memory serves I heard ARM Cortex utilizes a 3 core processor but I'd have to google it to verify.
 
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Just curious ,

Why no one is making CPUs with odd numbers of cores ? like 3 ,5 7 ,9 , 15 , 31cores?
In a way we do see an odd number of cores because the CCX's in a 3600 and 3900 have three cores each; but with two CCX's per CCD the odd number gets doubled. And doubled again with a 3900's two CCD's.

But of course the 4th core is still there in the CCX, just disabled because it didn't meet 'standard' for CPU performance. So I wonder if it has to do with design efficiency. It's obvious that one core is not going to cut it so 2 is the minimum to design around. That 2-core 'pattern' includes the design features and optimizations needed to access shared resources (caches, mainly) and becomes a building block, duplicated as needed to build the desired processor.

2 core building blocks, doubled in a CCX, further offers more options to harvest as many dies as possible for manufacturing efficiency which in turn allows marketing to create a segmented product line.
 
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Mr.Spock

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Dec 8, 2019
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single core CPUs are by definition odd. those still exist, Samsung SSDs had a 3-core controller, Athlon X3's have been produced.
but the short story is easier to load balance with 2 or multiples of two - the beauty of XOR.
 

jasonf2

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Oct 11, 2015
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While there is nothing keeping it from happening on a technical basis so much optimization was done for 4 core systems that odd core counts potential may be underutilized by some software. In parallelization you "split" the processes into multiple threads. Developers optimize as much as possible. As most core counts are even breaking loads out into even thread counts will give you optimal performance in most cases. Also good die layout depends on packing as much stuff on a chip as possible. Having even numbers of cores makes for more efficient layout when the cores are the same. Odd core count has been more prevalent when big little core sets are used or cores are purposely disabled for yield. This is again due to silicon use efficiency where one big one stacks well against two small ones. In yield cases there are more than likely still even cores on the die, just disabled.
 
Everything in computers is generally a power of 2--2,4,8,16,32,64,128,256,512,1024,2048,4096,16384,32768,65536,etc. (all I could do from memory :D)

Now if you have 3 cores you would be trying to divide these power of 2 numbers by 3. Some of these work well, but others are really messy so it doesn't make as much sense as a 2/4/6/8/10/12/etc core system.
 
Hi @nofanneeded

AMD did with their Tri core CPU's. As with any CPU really, but in years past, AMD was known for some of their CPU's having some of their cores locked, namely their earlier unlocked "Black Edition" (Tho those CPU's weren't only known for this) CPU's being able to be unlocked if paired with the correct motherboard and a healthy dose of luck.

Such as the AMD dual Core 7750 BE. There were a TON of people that were able to "unlock" an additional 2 cores on this particular CPU. Sadly while I still have my 7750 BE (and it still works) I was unable to get the additional 2 cores to run stable and so kept it "locked" at the stock 2. I remember I spent BANK on the mobo as well. I remember I drove 90 minutes to pick it up at a Fry's in another city. The name of it eludes me but I have it as well locked away in storage.

As for other odd # of CPU's, they are out there. I would hazard a guess that they are not a good overall use of silicone during the manufacturing process. If memory serves I heard ARM Cortex utilizes a 3 core processor but I'd have to google it to verify.
Exactly, even x3 processors were actually 4 core with one disabled/deactivated (in various ways) because they didn't make it as "healthy" at same standards as other cores. If they were not far off they could usually be activated using some higher voltage if BIOS would allow it.
 

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