4GB
192 Gigabytes is the maximum.
64 GB
over 9000
512 gb of ram
The maximum amount of RAM supported by Vista is 128 Gb (Ultimate, Enterprise and Business).
The maximum RAM supported by Windows 8 64-bit is 128 GB. This limit is applicable to the standard edition of Windows 8; other editions, such as Windows 8 Pro and Enterprise, also support this maximum. However, the actual amount of RAM you can use may also depend on your motherboard and hardware specifications.
The official minimum for a 64-bit installation is 2 GB of RAM. There is no "recommended" amount, as it depends on what you are trying to do. The maximum supported depends on what edition you are using: Windows 7 Professional and Ultimate support 192 GB of RAM. Windows 7 Home Premium supports 16 GB of RAM. Windows 7 Home Basic supports 8 GB of RAM.
4GB
According to the table in the Wikipedia article (see related link) - the maximum supported RAM is 4GB.
The maximum amount of RAM supported by a computer depends on the processor and the motherboard.
Approximately 3GB of RAM is the most that Windows XP 32 bit will recognize. ^^^^^^^^^^^^^^^^^^^^^ Right but wrong.... 4Gb of RAM is the maximum amount that can be addressed by a 32 bit operating system
4gb ram