Wikipedia has good documentation on binary representation of floating-point numbers

• single precision, 32 bits
• double precision, 64 bits
• floating-point arithmetic

Additionally, these Julia notebooks have nice viewable, interactive demos of floating point numbers and arithmetic from a Julian perspective.

• Floating point numbers, Sheehan Olver, University of Sydney
• Rounding and floating-point artihmetic, Sheehan Olver, University of Sydney

These notebooks are part of Sheehan Olver's series of Julia notebooks for MATH3976, Numerical Computing.