I am in the process of resurrecting an ancient desktop PC.

Managed to scrap the following configuration: (SOCKET 478)

Motherboard: As Rock P4i65g

Processor: Intel Pentium 4, 3.40 GHz (1MB cache)


VGA: ATI Rad-eon x1650 Pro 256MB (AGP x8/PCI)

Power Supply: 400W

Been searching for a better socket 478 motherboard, that has max RAM of 4GB, and I found a few... Like this one: MSI 865GM2-LS 478 Intel 865G Micro ATX Intel and this one: Gigabyte GA-8IG1000MK

Both have somewhat similar setup regarding chip set, CPU compatibility, VGA compatibility etc.. and both allow max RAM up to 4GB.

I found a few that also allow max. 4GB RAM but with one condition: "Due to the operating system limitation, the actual memory size may be less than 4GB for the reservation for system usage under Windows® 32-bit OS"

I am not sure what this means,my questions does it mean no socket 478 motherboard can have more than 2GB RAM or?


3 Answers 3


It's telling you that if you have a 32-bit OS and 4GB of RAM, then the OS will/may not report all 4GB as available, so it will appear some is missing.

This is due to a certain amount of RAM being statically set aside to be dedicated to the system devices on the motherboard (this does NOT include RAM that may be set aside for shared graphics adapter usage if your motherboard has it; that is something else, and is unrelated to the topic at hand).

When you use less than 4GB (say, 2GB) is dynamically shifts the allocated section around, making it appear that the full amount of RAM is available.

They do this as a trade off of capacity for speed. Statically allocated memory space for I/O is faster than dynamically shifting address space, but in most cases having more available RAM capacity is more beneficial to the end user.

Once you hit 4GB with 32-bit XP, then you are at your maximum capacity so it is more beneficial to statically allocate that reserved space than to make that ~12.5% of RAM capacity (assuming the usually seen/referenced 3.5GB available of 4GB).

Keep in mind, that these decisions were made when having 4GB of RAM was still a HUGE amount of RAM. Later, as more people started needing 4GB+ and 64-bit became more available/popular, there was no reason to revert the way it worked, because if you REALLY need all 4GB of RAM (or more), then you can/should switch to a 64-bit version of the OS.

More info is available in this SU Question/Answer(s): Why does Windows only show about 3.5 GB of my 4 GB of RAM?


If you want to use the full 4GB of RAM you will have, you should go for a 64 bit Windows. Here's an explanation of why the limit of 4GB is here:

The system can only use 4GB of RAM in 32 bit, but this also includes the amount of RAM that your graphic card has and all the memory needed by the buses, etc. So it means that if your GPU is 256Mb, you will only be able to use 3.75GB of your system RAM. For example, you will only have 3 GB of usable RAM if your GPU has 1GB of RAM.

Windows generally say's there's only 3.25 GB of usable RAM when you put more, even if your GPU is under 750 MB of RAM, but I don't remember why.

Unfortunately, not all Pentium 4 are 64 bit and Hyper-Threaded, can you be more precise about your Pentium 4 model ?

Moreover, if your Pentium 4 is Hyper-Threading capable, then it's worth upgrading to 3GB of RAM no more. Because if you're web browsing with the latest browsers, your CPU will be limiting you even before you can use over 3GB of RAM.

Generally, my rules are like that for RAM and processors:

  • 1 Core: 2GB of RAM
  • 1 Core Hyper-Threaded: 3GB of RAM
  • 2 Core: 4GB of RAM
  • 2 Core Hyper-Threaded: 6GB of RAM

And so on, you see the logic ;)

  • Edit: I do remember why: Windows also keep some RAM for the buses.
    – X.LINK
    Commented Oct 2, 2014 at 17:02
  • Pentium 4 - Prescott - 3.40 GHz - 800MHz - 1MB
    – Rhayader
    Commented Oct 3, 2014 at 7:45

Sandard 32-bit PC processors generally cannot address 4GB of RAM. Here's an article that explains it

  • A more accurate synopsis of the article would be that a 32bit desktop processor only has 4GB worth of addresses to hand out, and some of those must be used for video memory and other system components, leaving less than 4GB worth of addresses available for RAM. But kudos on the otherwise good answer. Commented Oct 2, 2014 at 16:02
  • 3
    @music2myear - This isn't a "good" answer. Its not even acceptable since all the author did, was provide a single sentence, then link to an article.
    – Ramhound
    Commented Oct 2, 2014 at 16:09
  • 2
    Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference.
    – Cfinley
    Commented Oct 2, 2014 at 16:35
  • 1
    This is incorrect. 32-bit processors can address more than 4 GB of RAM via PAE. Commented Oct 2, 2014 at 16:42
  • 1
    @ChrisInEdmonton It seems you're right superuser.com/a/604713/372392 Commented Oct 4, 2014 at 9:29

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