Before & After Under The Giant Lock

[binto]

Hi,

>From what I read in "The Design and Implementation of the FreeBSD
Operating System",said:
'However, most of the heavily used parts of the kernel have been moved out
from under the giant lock, including much of the virtual memory system,
the networking stack, and the filesystem.'

What the different "virtual memory system, the networking stack, and the
filesystem." before under giant lock & after moved out from under giant
lock?

I'm interest get deeper learn operating system, especially with FreeBSD..

Regards,
Binto