Find a string in the whole RAM

How to search a string in the whole RAM? (not only in some processes' allocated memory, but the whole RAM)

Or is there a way to dump the whole RAM into a 4GB or 8GB disk file? Then I could easily do:

grep mypassword c:\ramdump.raw

Usage example: I'd like to know if a password manager stores my master password in plaintext, as found by a security team here.

I'm using Windows 7 x64, as administrator.

Note: Unlike How to get complete memory dump in Windows 10? I specifically want to search content in the RAM, and not get information from a memory dump. Moreover this question is unclear: the title doesn't match the content ("Question in title doesn't seem to match the question in the body.")