100 in base 10 to base 2

The highest power of 2 in 100 is 2^6 = 64

100 - 64 = 36

The highest power of 2 in 36 is 2^5 = 32

36 - 32 = 4

The highest power of 2 in 4 is 2^2 = 4

4 - 4 = 0

so we're done, and putting these partitions together tells us

100_10 = 1100100_2