National Center for Supercomputing Applications Larry Brumbaugh William Yurcik National Center for Supercomputing Applications (NCSA) University of Illinois at Urbana-Champaign A Little Man Storage (LMS) Model

National Center for Supercomputing Applications Little Man Computer (LMC) Paradigm Developed by Madnick and Donovan During the 1960s, at MIT Taught to all MIT undergraduate CS majors Simplistic overview of how a computer actually works Adheres to von Neumann principles Authors have built multiple LMC simulators See: Newer version to be introduced at SIGCSE 2006 See Irv Englander text for LMC in the classroom

National Center for Supercomputing Applications Little Man Computer and the Walled Mailroom 100 mailboxes 1 inbox 1 outbox 1 calculator counter Little Man 10 assembler instructions

National Center for Supercomputing Applications Basic Hardware Components of LMS Storage Device Hardware Properties ID Numbering Schemes for the Component 3 cylinders0, 1, 2 (numbers are independent of the platter surface) 4 tracks per cylinder0, 1, 2, 3 (0/1 are the 1st platter and 2/3 are 2 nd platter) 8 areas per track0, 1, 2, 3, 4, 5, 6, 7 (same amount of data can be stored in each area) Platters rotate Access arm moves over the platter surface Data is copied to/from areas on the disk

National Center for Supercomputing Applications Areas on Both Sides of Platter 0 Labeling scheme: cylinder|track|area From 000 to 237

National Center for Supercomputing Applications Physical Components that comprise an LMS Storage Device

National Center for Supercomputing Applications Comparing LMC and LMS Characteristics Environment/Physical Act Compared Little Man Computer (LMC) Little Man Storage (LMS) historic relevance of paradigmfrom 1960’s to presentfrom 1970’s to present type of device describedcomputerdisk storage device actual hardware location of the Little Man itself CPU control unitstorage controller locations where data is stored 100 mailboxes (00-99); each holds 3 digit number; no ‘special’ mailboxes 96 disk areas ( ) each holds 512 bytes; two ‘special’ areas how I/O operations are performedread/write slips of paperread/write disk areas a programmable device? fundamental design principles yes! von Neumann model not really? standard disk + MS FAT

National Center for Supercomputing Applications LIST Structure for the Disk File Name Size (Bytes) Start Location (Area) Creation DateModify Date ALPHA.doc /03/200506/04/2005 X.Y.Z /18/199706/04/2005 NextFile1234.txt022512/25/200201/01/2004 ************** 20 byte names II Implemented as a White Board Stored in area 000

National Center for Supercomputing Applications Contents of Area 001 Showing Storage Allocation after Two Files are Written Area NumberNext Area Location in File (first free area) * 00100N(last free area) * (file continuation) (file continuation) (end of file) (file continuation) (end of file) N666 Called Area Utilization List (AUL)

National Center for Supercomputing Applications Basic I/O Commands Supported by LMS Command Op- Code Processing Performed by Command Create File00 Write an entry in the LIST, including name, create date, etc. Initialize one Free-Area-List area to ***End-of-File***. Delete File01 Erase the file entry line from the LIST. Return all of the files AUL entries to the Free-Area-List. Read File02 Begin in the LIST and then go thru the corresponding AUL entries. An alternative approach starts in the AUL table. Write File03 Add data starting with the first area on the free list. Write ***End-of-File*** after the last record is written. Append File04Follow the AUL entries for the file to the one containing 666. Add new records in a new area and replace 666 with new area #.

National Center for Supercomputing Applications Disk Status Following Several I/O Operations Area Next Area Area Next Area Area Next Area Area Next Area (ROOT) LIST AUL TableALPHABETA ALPHAGAMMA 01DELTA FREE 014 FREE 015 FREE 016 FREE 017 FREE FREE 021 FREE 022 FREE 023 FREE 024 FREE 025 FREE 026 FREE 027 FREE 028

National Center for Supercomputing Applications Disk Status After Additional I/O Operations Area Next Area Area Next Area Area Next Area Area Next Area (ROOT) LIST AUL Table FREE BETA FREE GAMMA 01DELTA SIGMARHOSIGMA FREE 02 FREE

National Center for Supercomputing Applications References [1] William Yurcik and Hugh Osborne, “A Crowd of Little Man Computers: Visual Computer Simulator Teaching Tools, “ Winter Simulation Conference (WSC), Cincinnati, OH. USA, December [2] William Yurcik and Larry Brumbaugh, “Using LMC Simulator Assembly Language to Illustrate Major Programming Concepts, ” The Proceedings of Information Systems Education Conference (ISECON), Cincinnati, OH. USA, November [3] William Yurcik and Larry Brumbaugh, “A Web-Based Little Man Computer Simulator, ” 32nd Technical Symposium of Computer Science Education (SIGCSE), pp , Feb [4] William Yurcik, Joaquin Vila and Larry Brumbaugh, "An Interactive Web-Based Simulation of a General Computer Architecture, " Proceedings of the IEEE International Conference on Engineering and Computer Education (ICECE 2000), Sao Paulo, Brazil, August [5] pdf SNIA Shared Storage Model White Paper

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