Like Windows 32-bit there are other versions that suffer from memory limitations including Windows Vista and Windows 7 Starter Editions.
These versions of Windows are commonly found on Netbooks*, and sometimes basic Notebooks / Laptops.
The limits of these versions are as follows:
Windows Vista Starter = 1Gb
Windows 7 Starter = 2Gb
Much like with Windows 32-bit you may be able to install more than 1Gb or 2Gb in the machine but the operating system will only be able to use the maximum as stated above.
*the Windows 7 Starter Edition memory limit does not directly affect Netbooks, as these machines mostly only have a 2Gb maximum supported by the machine.