Don't know about the 486 specifically, but this sort of thing wasn't unheard of. I have a pentium-era machine with 8MB EDO built into the board. It can stand alone or complement whatever you put in your DRAM slots (though curiously, if you max it out at 4x32MB, you get 128MB, not the 136MB you might hope for...)
Edit: wait... I thought we were talking about something unusual because he mentioned SIMMs, and the 486 specifically, but I guess he's just talking about the conventional memory on x86 that peaked at 640KB. This is not what I was describing above (that system has extended EDO built in in addition to the conventional 640).
Don't have a specific link for you, but just look into the memory model of the IBM PC, conventional vs extended RAM, etc... 640KB (or less!) was all we used to have, plugged right into DIP sockets.
When, in the late 80s, computing technology started increasing in power like mad, we quickly needed access to more RAM, but the original memory model held us back, so we had to hack around it in various awkward ways. So we ended up with the original on-board chips + SIMM expansion slots.
Looking back, we were so terribly shortsighted in our designs, and Moore's Law just continually blew everything to hell.
That's not what this is about. OP is talking about booting with just the external L2 cache (which I've seen vary from 64KB to 256KB) when no RAM SIMMs are plugged in.
So the cache can stand in for main memory when none was present? I'd be interested to see the implementation details, but alas, I must be going about my search wrong =(
Will have to look into it more when I have some more time.
Edit: wait... I thought we were talking about something unusual because he mentioned SIMMs, and the 486 specifically, but I guess he's just talking about the conventional memory on x86 that peaked at 640KB. This is not what I was describing above (that system has extended EDO built in in addition to the conventional 640).
Don't have a specific link for you, but just look into the memory model of the IBM PC, conventional vs extended RAM, etc... 640KB (or less!) was all we used to have, plugged right into DIP sockets.
When, in the late 80s, computing technology started increasing in power like mad, we quickly needed access to more RAM, but the original memory model held us back, so we had to hack around it in various awkward ways. So we ended up with the original on-board chips + SIMM expansion slots.
Looking back, we were so terribly shortsighted in our designs, and Moore's Law just continually blew everything to hell.