[plt-scheme] Bignums in Scheme

I am writing to inquire if you are aware of any articles/documents
that describe how bignums (arbitrarily large integers) are implemented
in Scheme. I am particularly interested in how bignums are represented
and the algorithms used for bignum arithmetic. I am also looking for
performance studies (speed and memory) that may exist. Both
descriptions of native implementations and use of foreign libraries
are of interest to me.

On a related note, are you aware of any garbage collection algorithms
for bignums?

I look forward to hearing from you. 

Best wishes, 

Marco