nbelote :
128GB on non-Pro, 512GB on Pro. x86 of any version is limited to 4GB.
There seems to be a lot of confusion out there about max RAM allowed by the various Windows versions. There are three factors that impact the max RAM you can have on any computer.
Factor #1: The hardware architecture of your computer. PCs have gone thru a long history of changing architecture, and of course, Windows has to follow that. Originally (30 years ago in the '80's) computers were only 8 bit capable - how many bits (or digits) a computer can count to. Then they came out with 16 bit architecture, which was a vast improvement in capacities it could count to (both hard disk AND memory (RAM), which are now essentially all archaic. Then the next leap was to launch 32 bit architecture, which still exist today (you can actually buy 32 bit machines today. And finally, 64 bit architecture was released, which is what is prevalent and the latest today (2015).
Factor #2 - Windows Hardware Support
Of course Windows had to grow with each change in the hardware, in order to accommodate the hardware advances. So, when 32 bit architecture came out, Windows also support that, and it could count only up to about 3.5 GB for RAM. And when 64 bit Architecture came out, soon after Windows supported that as well, which can address well beyond the 3.5 GB range.
Factor #3 - Windows Architecture
Once 64 bit hit the streets, Windows was scrambling to be able to take advantage of this new hardware architecture. So, at first, the 64 bit support provided by Windows went up to only 16 GB on the Home Versions on 64 bit architecture hardware, and later versions (Business, Ultimate, and Enterprise for Vista) went up to support of 128 GB, and for Windows 7 and 8.x went up to 192GB max RAM support. It I expected that Windows 10 will follow the same RAM support limits as Windows 8. But keep in mind, that to be able to have such large amounts of RAM means that the PC hardware can also support that amount. Most 64 bit PCs and laptops support only up to 8GB, while the recent trend has been to make the limit 16GB, and even nicer PC can go to 32GB. To go beyond that capability in the PC hardware usually requires it being a 'server' - a machine built ti handle a lot more RAM.
Hardware Explanation
Memory is built on memory sticks, which are then simply inserted into 'memory slots' on the motherboard of the computer (the part that holds all the key portions of the computer, including the CPU). So, some computers are built with only to memory slots (the max higher end laptops when they have more than just one memory slot), and most desktops are built with 4 memory slots, while server have a lot more. So then, the max any computer can support hardware wise for its memory will depend on how big a memory stick each slot can support. This varies greatly, whereas the more modern PC (motherboards) can support 8 GB per slot. Older computers could only support 1GB per slot, more recent one could support only 2 GB per slot, and even more recent one could typically support only 4 GB. Just about all of today's computers can support 8GB per slot, but not all have 4 memory slots!
So, you can now see how this 'max memory' issue becomes very involved, complicated and confusing. So, the bottom line is that it is a combination of the hardware architecture (32 bit vs 64 bit), the actual individual computer's architecture (how many memory slots it has and what size of RAM each one can handle), and what is the Windows version (XP, Vista, Windows 7, Windows 8/10), and sub version that is in consideration (Home Edition or Professional/Ultimate/Business).
To get a real in depth description of what version of Windows what max RAM is can support, go to:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa366778(v=vs.85).aspx
and follow its links to the individual Windows version you are using or considering..
Facebook
Twitter
Instagram