The difference between mips*-gnu and mips*-linux when configure tool-chain

["Fu, He Wei PSE NKG" <hewei.fu@siemens.com>]

Hello everyone.At the time of building tool-chain for mips machine,we
can choose mips*-gnu or mips*-linux, I want to know what's the
difference between them? The original idea is that mips*-gnu for
developing firmware which has not OS-surport, and mips*-linux for
developing software on Linux, but it is not suitable for firmware such
as bootloaders.But now I think I'm not right,it seems that configure
with mips*-linux suit for both linux and bootloader, and configure with
mips*-gnu means build for OS such as IRIX surport, I'm not very
clearly,can anybody help me figour out the difference between them?
Thanks