caching - Cache and scratchpad memories -

could explain difference between cache memory , scratchpad memory? i'm learning computer architecture.

a scratchpad place keep stuff. cache, memory talk through not talk at. scratchpad post note, write on , keep you. cache paper send off else instructions memo.

cache can in various places, layers (l1, l2, l3...). both scratchpad , cache sram in chip, address , data bus , read/write/etc control signals. (as many other things in computer may or may not used addressable ram). during boot, before ram on far side (slower ram side, processor being near side) initialized (eventually dram typically if have cache otherwise why have cache) may possible access cache addressable ram. depends on system/design though, there may control register enables behave simple ram, or there may mode, or normal mode may such long dont address more size of ram based on alignment (perhaps 32k ram between 32k boundaries) may not try evict , generate bus cycles on dram/slow/far side of cache allowing use ram scratchpad.

but, normal use case cache ideally invisible pathway ram. dont access cache ram using cache addressing use address space of ram beyond , cache allows processor continue without waiting slow ram.

talking booting again, think kinds of things need when booting, namely bringing dram controller, non-trivial thing. having on chip memory allows if nothing else temporarily have ram small stack , variables. can example compiler on compiled language c needs @ minimum ram stack , variables. depending on space can put program there too, running there faster flash. alternative having no ram having write dram init in assembly using general purpose or other registers in processor, taking complicated task , making more difficult. once main system ram up, may or may not choose not use on chip (scratchpad) ram.

i , argue if want test dram see if working need not use ram test ram, test program should not run in nor use ram under test. having scratchpad ram on chip (or other ram in address space, perhaps video card ram example) used dram test program. unfortunately lots of folks use ram under test hold stack , program , variables , heap program doing test, leaving important parts of ram untested other 1 or small number of patterns.