Default paging is what it already comes with. It is a pre-made template, while custom paging would be ones on ideas and creativity.
Difference between paging and what?
Nothing -- they are the same thing.
By default the paging file 1.5 times the size of the RAM installed
It is paging.
By default partition 0.
In demand paging, a page is not loaded into main memory until it is needed. In pure demand paging, even a single page is not loaded into memory initially. Hence pure demand paging causes a page fault. Page fault, the situation in which the page is not available whenever a processor needs to execute it.
One an a half times installed memory size.
In case of simple paging all pages should be in main memory to run a process..while in case of virtual memory paging pages can be loaded as needed by the processor i.e. called demand paging...
Start->Control Panel->System->Advanced->Perfomance Settings->Advanced->Virtual Memory Change. Choose a hard drive where you want to put the paging file, then custom size.
Because many systems only have one partition.
boot partition
Boot Partition