Hello,
What is north and south bridges in computer...

 

Hello,

Have a look at these pages of the wiki:
https://en.wikipedia.org/wiki/Northbridge_(computing)
https://en.wikipedia.org/wiki/Southbridge_(computing)

Bertus

 

why ram is called random?

 

Hello,

Read this:
https://en.wikipedia.org/wiki/Random-access_memory

Bertus