Originally posted by Woolie Wool
If cache = system memory, I have 512 MB (the only cache I'm really familiar with is the one for my browser). Plus 60 gigs of HD space.
I don't think I've ever even seen system RAM referred to as cache, before. Cache, insofar as I understand, refers to the on-chip fast memory* - and IIRC the highest for home PCs is something 1-2MB(?).
( *Cache is used to temp store data, so the chip can fetch it locally - and thus very quickly - rather than having to go all the way across the data bus to fetch from RAM. Recently accessed data is backed up - from RAM - onto the cache.
The CPU first checks the cache before going all the way to RAM to fetch data. Cache is normally over 2 levels. Level 1 is, IIRC, direct mapped so that every cache address directly corresponds to a RAM address range. This gives fast search time, but reduces free memory as each cache address is constrained to a set of data. Level 2 is fully associative IIRC - i.e. it's a generic pool where data from any address on RAM can be put in any cache address. It's slower to search, but you can put the data anywhere within it, so it's more space efficient. The CPU will search L1 then L2 then RAM.
Of course, you can have more than 2 cache levels, but I think the convention is currently to use 2.
See also 'cache' at
http://www.2002.arspentia.org/8lb3oz/gamecube which is decent explanation of L1 & L2 caching on the Gamecube.
Cache also exists on HDDs (reduce seek time by local storage on the HDD cache) and I believe on GPUs as well. )
