That’s exactly what is done during bring up of new SoCs. Memory controllers are either non-functional in early prototypes or a miniature design is put into a bunch of FPGAs with only a single core and caches. The cache lines and TLB entries are primed and pinned with all relevant code and data pages before booting up a kernel.
I think this is also what happens at boot on most systems before RAM is initialized, so maybe boot times could be faster if they took advantage of caches getting larger?
Not sure if you meant to point out something else but initramfs or ramdisks are loaded on to RAM itself which is already up and running at that point. RAM initialization is usually initiated by early boot firmware and information about the physical address map is eventually passed on to the OS kernel which later sets up paging (virtual memory).
On coreboot this boot method is called CAR, Cache as RAM, pretty interesting usage of cache to be honest, no need to add separate SRAM if you already have some
https://en.wikipedia.org/wiki/Tiny_Core_Linux
There are <100MB Linux distributions. Is it theoretically possible to run an entire operating system without RAM, purely in CPU cache?
That’s exactly what is done during bring up of new SoCs. Memory controllers are either non-functional in early prototypes or a miniature design is put into a bunch of FPGAs with only a single core and caches. The cache lines and TLB entries are primed and pinned with all relevant code and data pages before booting up a kernel.
I think this is also what happens at boot on most systems before RAM is initialized, so maybe boot times could be faster if they took advantage of caches getting larger?
Not sure if you meant to point out something else but initramfs or ramdisks are loaded on to RAM itself which is already up and running at that point. RAM initialization is usually initiated by early boot firmware and information about the physical address map is eventually passed on to the OS kernel which later sets up paging (virtual memory).
On coreboot this boot method is called CAR, Cache as RAM, pretty interesting usage of cache to be honest, no need to add separate SRAM if you already have some
The 7995WX has 384 MB L3 cache.
Imagine what you could do with that!
not only possible people have done it. dunno if theyve done it on amd but some soc have.
Xeon Max will boot without any RAM installed at all. Though I’m not sure it counts, considering it has 64gb built into the cpu.