Answer 1

register keyword is used for the variables which are heavily used . In order to speed up ur program .as these variables are stored in CPU registers
Register in CPU means these are the fastest storage location within the CPU .... These register inside CPU are faster than your RAM and as the data is held with in CPU ; its easy for the CPU to process and hence makes it fast . These registers are small in size (4bytes for a 32bit processor and 8bytes for a 64bit Processor)