This paper presents an algorithm for reclaiming unused free storage memory cells in LISP. It depends on availability of a fast secondary storage device, or a large block of available temporary storage. For this price, we get: 1.) Packing of free-storage into a solidly packed block. 2.) Smooth packing of arbitrary linear blocks and arrays. 3.) The collector will handle arbitrarily complex re-entrant list structure with no introduction of spurious copies. 4.) The algorithm is quite efficient; the marking pass visits words at most twice and usually once, and the loading pass is linear. 5.) The system is easily modified to allow for increase in size of already fixed consecutive blocks, provided one can afford to initiate a collection pass or use a modified array while waiting for such a pass to occur.
