Here is what the standard C99 (ISO-IEC 9899 6.2.5 §10) or C++2003 (ISO-IEC 14882-2003 3.1.9 §8) standards say:
There are three floating point types:
float,double, andlong double. The typedoubleprovides at least as much precision asfloat, and the typelong doubleprovides at least as much precision asdouble. The set of values of the typefloatis a subset of the set of values of the typedouble; the set of values of the typedoubleis a subset of the set of values of the typelong double.
The C++ standard adds:
The value representation of floating-point types is implementation-defined.
I would suggest having a look at the excellent What Every Computer Scientist Should Know About Floating-Point ArithmeticWhat Every Computer Scientist Should Know About Floating-Point Arithmetic that covers the IEEE floating-point standard in depth. You'll learn about the representation details and you'll realize there is a tradeoff between magnitude and precision. The precision of the floating point representation increases as the magnitude decreases, hence floating point numbers between -1 and 1 are those with the most precision.