Why are CPUs more expensive than RAM?

Question

Something I never understood is that CPUs have a tiny die area (the size of your fingernail), but cost on average 4 times as much as a Memory DIMM, and a DIMM has maybe 20 or more memory chips that are each bigger than a CPUs die area, yet DIMMs are much cheaper than CPUs.

I know RAM chips are usually one generation behind CPUs for the size of the transistors, 32nm vs. 22nm, and there are much greater research costs for CPU development, but it still does not take into account the huge price difference per mm² of silicon.

Answer 1

If you just consider the quantity of the silicon, you could use the same logic to argue that a CPU should cost less than a sandbag.

But a CPU is much more architecturally complex than a DIMM or a sandbag. Economic forces such as the costs associated with R&D, manufacturing, packaging, patenting, licensing, litigation, marketing, advertising, competition, etc., all also contribute to the final cost.

That said, your original assertion is unfortunately an apples-to-oranges comparison and does not always hold true unless you restrict the sets of CPUs and DIMMs you're comparing. Even if you only consider products currently available through common retail channels, it is not difficult to find a CPU that costs less than a DIMM.

Answer 2

A CPU with some defects generally has to be thrown away. Occasionally you might have a die that has a lower end model with fewer cores or less cache and a bad core or bad cache section can be disabled. But generally, a CPU has to be perfect or it goes in the trash.

By contrast, a DRAM chip is a giant array of identical chunks. If there's a bad chunk, a good chunk can replace it. By creating a very small number of extra chunks, even a die with several failures can be salvaged by disabling the bad chunks and replacing them with spares.

This means the percentage of dies that make it to packaging is much higher for CPUs than for RAM. This is just one factor, but it's an important one.

Answer 3

CPUs are not generally more expensive than RAM. It depends on what quality and kind of CPU and what quality kind of RAM; also, on how much RAM vs "how much" CPU (e.g. number of cores).

For example, a 2x64 GB set of DDR4 2400 DIMMs would set you back about 2,000 USD, while an AMD Ryzen ThreadRipper 1950X costs ~670 EUR.

Now, you could say "oh, I'll get cheaper memory and not as much of it." Fine, then: I can find you a 5 USD 64-bit quad-core processor, now try and beat that...