For a long time now, I've been pondering buying a netbook, but not just any netbook. I have very specific requirements.
When the Asus EEE PC 1015pem, with the Intel Atom N550, came out, I almost bought it, but there was one catch – maximum 2GB of RAM, which is just a tad low considering what I need, or at least what I think I need. Better to be on the safe side anyway.
So I held my breath, pondering, scheming and then suddenly, BAM, Intel released the N570, which apparently can support 4GB of RAM. Saying apparently since I haven't been able to find anywhere on their site, where I can confirm the information and the processor specification isn't complete yet for some reason, but I do believe it to be true for other reasons. Among other things, this CPU will also be used in servers.
However, every single netbook manufacturer, who have put specs out for netbook sporting the N570, have included a limit of 2GB.
Where then do the limitations lie? Is it at all likely that it can be circumvented, assuming that the manufacturers do not change the specs?
I don't think it's likely that the CPU would be the limiting factor, so what about the rest of the hardware? As far as I know, the memory controller is built in to the CPU, so that probably won't be it either. I suppose it could be a BIOS limitation.
What do you think?
Best Answer
I tried a 4G memory module, single rank which has identical pinouts (signals) as the 2G module except for chip select and clock enable (but with the same pin assignments) and it would not work. I then hardwired the chip select and clock enable lines in various configurations to guarantee activation at least half of the memory present (2 GB, like that of the 2 GB module) and that failed as well.
The ram modules have a PROM onboard that store characteristics of the memory module, like speed, latency, burst mode, etc (device parameters). Also, the absence of one additional A/D line (of the 204 pins present), say removed from the trace bus on the motherboard, is all that separates a 2 GB module from a 4 GB module, address/data buswise. Its possible to remove the trace line but that's not realistic or practical as a hardware limitation, although technically feasible.
Getting back to the PROM, the N570 CPU with its memory controller interrogates the memory module to find out what type it is and how it should configure itself to work with it. There are common (shared) bus & I/O lines used during power up that allow the CPU to do this, even though the CPU doesn't know yet which type it is working with.
If the BIOS determines that the memory at boot up is 4 GB (or greater) it may refuse to work with it, as a self imposed limitation of the BIOS design. That's why, for example, no one has got past boot up using any of the available 4 GB memory modules. This is where I believe the problem lies, not with the hardware or memory. Fix the BIOS and you should be able to handle 4 GB RAM on your netbook. Anyway that's my conclusion.