Dear Mike
Because of the format of the SA transaction file(s), they will not decrease in overall size after archiving a segment (or all) of the data, but will 'fill up' with new transactions as they are retrieved into SA.
Having said that, there is no separate 'Purge' function...the option Archive / Purge describes the complete function - not two separate ones.
To make room on your hard drive now that you have archived some data, you may want to copy (or zip) the archive files and put them in another location (CD or zip disk), then remove them from the data directory so that these new files do not use up precious space. The archive files have the syntax "SRARnnnn", where "nnnn" is replaced with the archive file number.
I can assure you that when you choose to 'Archive' data - it is removed from the SRTRANS file. You can observe this by using the Online Inquiry option to view the data you archived...it should not be there after having run the function.
Again, even though the actual transaction file size will not decrease - you should see a marked increase in performance.
Hope this clarifies the Archive function!
Regards 