4 ms·

Reminds me of the 486 motherboard which would boot DOS with no SIMMs (RAM) in it. It had 64 kbyte cache on the motherboard...

mtrower 8y ago
That's not cache, friend - that's main system memory =) (and 640KB by the time of the 486) (though, speaking of cache, the 486 was the first chip in the family to have L1 cache - a whole 8KB of it!)
- 0xcde4c3db 8y ago
  Parent specified a board with SIMM sockets, which would contain main memory. The 486 family supported external L2 cache, for which 64KB would be a plausible size.
  - mtrower 8y ago
    Did SIMM RAM straight up replace the DIP chips when it was introduced? For some reason I thought they were used in parallel, with conventional RAM physically separate from the rest. I guess there's no reason that should have to be, though, as the 640K barrier was a real mode limitation, and nothing more. What they say about assumptions applies. I guess I kind of missed out on the fun here, going straight from an XT to a Pentium...
    - 0xcde4c3db 8y ago
      > For some reason I thought they were used in parallel, with conventional RAM physically separate from the rest. I don't specifically know of any boards like that, but Pre-Pentium boards were kind of a free-for-all, so I wouldn't be a bit surprised if they exist.
fb03 8y ago
Wait, wow, I've never heard of this. Do you have a link of this phenomena?
- mtrower 8y ago
  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.
  - Narishma 8y ago
    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.
    - mtrower 8y ago
      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.

mtrower 8y ago

That's not cache, friend - that's main system memory =) (and 640KB by the time of the 486) (though, speaking of cache, the 486 was the first chip in the family to have L1 cache - a whole 8KB of it!)

0xcde4c3db 8y ago
Parent specified a board with SIMM sockets, which would contain main memory. The 486 family supported external L2 cache, for which 64KB would be a plausible size.
- mtrower 8y ago
  Did SIMM RAM straight up replace the DIP chips when it was introduced? For some reason I thought they were used in parallel, with conventional RAM physically separate from the rest. I guess there's no reason that should have to be, though, as the 640K barrier was a real mode limitation, and nothing more. What they say about assumptions applies. I guess I kind of missed out on the fun here, going straight from an XT to a Pentium...
  - 0xcde4c3db 8y ago
    > For some reason I thought they were used in parallel, with conventional RAM physically separate from the rest. I don't specifically know of any boards like that, but Pre-Pentium boards were kind of a free-for-all, so I wouldn't be a bit surprised if they exist.

fb03 8y ago

Wait, wow, I've never heard of this. Do you have a link of this phenomena?

mtrower 8y ago
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.
- Narishma 8y ago
  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.
  - mtrower 8y ago
    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.