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Computing in the DSP arena has seen processors go from 8-bit to 16-bit to 24-bit to 32-bit to 64-bit word sizes. Because of dynamic-range considerations, until the 32-bit word size was reached, the entire word size was devoted to mantissa. With 32 bits, however, the convenience of floating-point has dominated and word sizes are split into, typically, 8 bits of exponent and 24 bits of mantissa, doing away with the 32-bit mantissa.
One gets the impression that dynamic range limitations have essentially disppeared with the use of floating-point notation. There are problems, however. The exponent is simply an attenuator which acts to control SINGLE-TONE dynamic range. If maximum TWO-TONE dynamic range is desired using a 32-bit word, the 32-bit mantissa is preferable to the 24-bit mantissa. TWO-TONE dynamic range is in the mantissa, not the exponent. For more details, see section on DYNAMIC RANGE