I am havind almost 50 gb free space in hard disk. But while partitioning its shows that could not allocate requested partitions : no partition slots in sda. I made free space by shrinking my current 'e' drive.
Error while Installing centos 6.7 alongside windows 7
centos;partition
MBR only supports four primary partitions and you probably already have partitions C,D and E plus a boot partition. So you would need to delete one partition and/or reformat it. For details see https://en.wikipedia.org/wiki/Master_boot_record.