Why are Intel E-Cores 1/4th the size of P-Cores

Among other things, they do less per clock, which likely means fewer adders and other compute units, smaller storage to support a smaller amount of out of order operations, etc.

The E-Cores are an extension of the Atom cores, so you may be able to find older articles comparing their die size and structure to 'Core' cores. They've been about 1/3rd to 1/4th the size and around 1/2 the performance of similar age designs through most of their lifetime.

I would imagine the P-Cores have other dedicated circuitry for various features that the E-Cores lack. I believe the intent for this hetrogenous setup is to be akin to the big.LITTLE topology used in ARM systems.

Personally I'd like to see Linux/Windows perform when if scheduled to exclusively run on the E-Cores.

Any reduced functionality implies reduced area: the interesting question is choosing features given some area and power objective.

For example, fast (and hot) AVX-512 with a large area, slow AVX-512 with a reduced area, or no AVX-512: having the extension on the P-Cores only was deemed enough.

Less cache, much smaller OOO window, AVX-512. E-core is an area play so Intel can score some multi-thread benchmarketing wins on integer heavy code that don’t have larger memory/cache footprints, don’t require much speculative depth, and naturally have high amounts of ILP. They completely fall flat on plenty of workloads. And the way Intel runs them is absurd: 10+ watts per e-core just to eek out a MT win is pure absurdity.

Until Intel has a p-core that isn’t grossly obese, they have no option but to spam e-cores just to make powerpoint slides.

No AVX-512, less cache, lower frequency only one thread per core.