Version 1.3 implements a new internal design for arrays:

Extensive redesign of array data structures to support large arrays and
fast access to arrays created with split.  Many of the ideas in the
new design were inspired by reading "The Design and Implementation of
Dynamic Hashing Sets and Tables in Icon" by William Griswold and
Gregg Townsend, SPE 23,351-367.

Bug reports, comments, questions, etc. to 
Mike Brennan, brennan@whidbey.com.
ftp site: ftp.whidbey.net in ~/pub/brennan