Long(INT64) is for integers that have the maxvalue of 9,223,372,036,854,775,807
Long is stored in 64bit and 64 bit = 8 bytes. 1 byte can be written in a hexadecimal number with the max value of FF(F=16) per byte. So 8 bytes have the maxvalue as 0x7FFFFFFFFFFFFFFF in hexadecimal or 9,223,372,036,854,775,807 in decimal.
Also, there is short(int16) which stores in 2 byte and have the maxvalue of 32767
Hope you understand
Ref:int16:http://msdn.microsoft.com/en-us/library/system.int16.maxvalue(v=vs.110).aspx
Ref:Int64:http://msdn.microsoft.com/en-us/library/vstudio/system.int64.maxvalue