1.  Sowmiya Chocka Narayanan

2.  Problem Statement  Free listed exhausted!!! Mission Reclamation  Solution proposed  Newell, Simon and Shaw placed the responsibility on the user  Keeping track of lists, sub lists, shared lists make it painful  Reference Counting  Too much of bookkeeping involved  Haunting Circular lists  Invoking a special procedure to mark and collect  Additional storage for handling branch points or higher frequency of retracing the list  Sign reversal of whole words  Handling multiple word lists

3. Step 1: Step 2:

4. Step 3: Step 4:

5. Test Bench Storage Requirement HighlightLowlightSpeed WISP list Routine 68 words, 2 index registers and accumulator Can trace any list structure with any no. of branch points Bigger routine1.85 sec Wilkes Routine 35 words, 2 temporary locations Lesser storage Could get lost in a circular list 2.75 sec Branch point stored Routine 34 words, 48 words for branch points Parts of List structure traversed only once No. of branch points less than 49.448 sec

6.  Portability is best achieved by writing the garbage collector in a higher level language  Trace phase can be written in high level language  With support for extra low level operations like setting an element minus, setting branch point flag, testing sign etc.  The sweep phase is machine dependent

7.  Case 1  Each list element has n consecutive registers  Handled similar to list with single register  New Free list element occurs at every nth location in free store

8.  Case 2:  Head of first register contains register count  Follows same Mark phase as case1, returns a single free list element consisting of largest discarded register block  Addresses the problem with negative data word

9. Threaded List System Split List System

10.  What we saw so far..  Are the experiments mentioned thorough and sufficient?  What about the pause time aspect of the system?

11.  [1] Newell, A. Information Processing Language V Manual. Prentice-Hall, Englewood Cliffs, N.J., 1961.  [2] John McCarthy, Recursive functions of symbolic expressions and their computation by machine, Part I, Communications of the ACM, v.3 n.4, p.184-195, April 1960  [3] Daniel G. Bobrow, Daniel L. Murphy, Structure of a LISP system using two-level storage, Communications of the ACM, v.10 n.3, p.155-159, March 1967  [4] M. V. Wilkes, Lists and why they are useful, Proceedings of the 1964 19th ACM national conference, p.61.1-61.5, January 1964