Until 64 bit CPUs and OSes became mainstream, it was not easy to use more than 4GB on a 32bit system (or even 2 in Windows XP, later raised to 3.1-3.5-ish with

Until 64 bit CPUs and OSes became mainstream, it was not easy to use more than 4GB on a 32bit system (or even 2 in Windows XP, later raised to 3.1-3.5-ish with the /3GB switch in boot.ini). You had to use PAE (Physical Address Extensions - https://en.wikipedia.org/wiki/Physical_Address_Extension https://en.wikipedia.org/wiki/Physical_Address_Extension ), basically a 3-level page table structure, provided the CPU and the OS offered it. It could cause a few compatibility woes with binaries not expecting it, esp. stuff running in kernel mode, and of course in the Microsoft world it was used as an excuse to charge you more - the "Standard" versions of Windows server x32 were limited to 4GB, forcing you to buy "Advanced/Enterprise/Datacenter/Whatever" SKUs. So anyway 4GB was the maximum it would make sense to install on Windows for a long time, pretty much until 64 bit CPUs and Windows 7 became common (Deliberately omitting Vista, which so many opted to skip).