Bit vectors vs. fixnums

[charest@AI-SUN.JPL.NASA.GOV (Charest)]

I have an application in which I want to implement a set of boolean
properties as a "array" of bits. I am doing this to minimize the 
memory consumed. 

I am stuck between using bit vectors or fixnums in my implementation.
Bit vectors seem "conceptually" appropriate, but do they eat more 
memory than a fixnum of the same size as allocated by SCL? And are the 
bit vector bit-manipulation functions more or less efficient than 
the fixnum bit-manipulation functions? On the other hand, is one 
implementation more flexible than the other?

	Thanx in advance,

	Len Charest