Question

one point of difference between Boot sector virus and file virus

Answer 1

boot virus infect the boot record
file virus infect executive files

Answer 2

Boot sector virus-it becomes active at the time of booting the machine.
Eg-Disk killer

File virus-it remains in the memory until user runs another program.As soon as another program is used,the virus copies itself and infects other files on the disk
Eg-Cascade

Hope it helps you!!