There’s a rumor going around that AMD is going to build a 10-core Ryzen 4000 CPU, possibly as a direct challenge to Intel’s Core i9-10900K. The source of the rumor is a claim by Yuri “1usmus” Bubliy, who has previously also claimed to create power profiles capable of improving performance over AMD defaults. Our own testing of the power plan did not support this claim when we reviewed it, and there’s little reason to believe these 10-core rumors:
About Zen 3. Part 2.
— Yuri Bubliy (@1usmus) September 7, 2020
No, it isn’t — but how do we know that? The clues are in the way Ryzen is structured. The basic “unit of Ryzen,” if you want to refer to such a thing, is a quad-core CPU and its associated cache (AMD calls this a CCX). AMD does offer dual-core Ryzen-class CPUs, but it doesn’t offer any core counts that are multiples of two but not four in the rest of the stack.
There are three ways for AMD to support a 10-core chip:
1). Build a new CCX architecture based around a block of five chips instead of four, with a total of 10 chips per chiplet instead of eight.
2). Build a brand-new memory controller and pair it with a different package design.
3). Threadripper 2990WX.
There’s no word that AMD is bumping core counts with the Ryzen 4000 family and the market is still digesting the core count doubling AMD delivered in 2019. AMD has settled on 16-cores as the boundary between enthusiast and workstation hardware. Manufacturers also don’t tend to use odd numbers of CPU cores (AMD’s triple-core Toliman CPUs were an exception that proves the rule).
AMD’s third-generation memory subsystem connects one dual-channel memory controller to each chiplet. It could theoretically disable one memory channel per controller and use two controllers, with a memory connection to each chiplet — but that still creates a lopsided configuration in which eight cores are fighting for a single channel of memory bandwidth. The other two cores would share an equally wide channel. AMD would have to rewrite its algorithms to tell the eight-core chip to preferentially push traffic over the connection and through the other CPU. The 2990WX approach, with the memory controller connected to one chiplet and the second chiplet hanging off the first is a step backward.
But there are non-technical reasons for AMD not to release a 10-core chip, too. Instead of meeting Intel core-to-core, AMD has chosen to bracket Intel with 8-core and 12-core CPUs. This is advantageous to the company. Currently, a 12-core AMD CPU is typically faster (at least in multi-threaded code) than an Intel equivalent. Intel’s 10-core may beat an AMD eight-core, but AMD makes certain you pay a hefty premium to step up to it — while making their own 12-core look like a very nice performance bump. Inserting a 10-core part into this stack would muddy it in a way that isn’t necessarily to AMD’s advantage.
These factors collectively indicate that AMD will not launch a 10-core part in October.