System Software

339.022 2KV Mössenböck Th 13:45-15:15 HS 19 Begin: 08.10.2020

Due to Covid-19, this course is delivered in "hybrid mode", i.e. it takes place in HS19 and is also streamed and offered for later download.

All students who registered for hybrid mode on Doodle can participate directly in HS19. Since less than 45 students registered, those students can attend physically in every week.

The other students can attend the lectures online under or can download the lecture videos from this web page (see below).

Chances are high that the exam will also have to take place in online mode. The final decision will be made in November. The requirements and the procedure for online exams at our institute can be found under

This course is a KV (combined course consisting of lectures and project work) in which you will learn the concepts and the implementation of various system software components such as garbage collectors, linkers, loaders, debuggers and text editors. In addition to the principal algorithms the course will also discuss case studies of such programs. The course is given in English. It is part of the Major Subjects Software Engineering and Computational Engineering in the Computer Science Master programme.

Lecture Times

Date Topic Video
08.10.2020 Memory Management download
Garbage Collection download 1
download 2
download 3
Linkers/Loaders download 1
download 2
19.11.2020 Debuggers download
26.11.2020 Text Editors download
rest Project
03.12.2020 Exam
08.01.2021 Project submission


1. Memory Management
   1.1 Overview
   1.2 Allocation and deallocation of memory
   1.3 Simple free list
   1.4 Multiple free lists
   1.5 Buddy system
   1.6 Memory fragmentation

2. Garbage Collection
   2.1 Motivation
   2.2 Basic techniques
       2.2.1 Reference Counting
       2.2.2 Mark & Sweep
       2.2.3 Stop & Copy
   2.3 Variants
       2.3.1 Mark & Compact
       2.3.2 Generation scavenging
   2.4 Incremental garbage collection
       2.4.1 Tricolor marking
       2.4.2 Train algorithm
   2.5 Finding root pointers
       2.5.1 Pointer tables
       2.5.2 Conservative garbage collection
   2.6 Garbage collection in multi-threaded systems
   2.7 Finalization
   2.8 Case study: Java Hotspot VM
   2.9 Case study: .NET

3. Linkers and Loaders
   3.1 Overview
   3.2 Case study: Oberon
       3.2.1 Run-time data structures
       3.2.2 Resolving external references
       3.2.3 Load algorithm
   3.3 Case study: Java
       3.3.1 Overview
       3.3.2 Class files
       3.3.3 Loading phases
       3.3.4 Example: custom class loader
   3.4 Linking/loading in C/C++

4. Debuggers
   4.1 Architecture
   4.2 Case study: Java Platform Debugger

5. Text Editors
   5.1 Data structures for texts
       5.1.1 SimpleText
       5.1.2 GapText
       5.1.3 PieceListText
   5.2 Text representation on the screen (case study)
       5.2.1 Line descriptors
       5.2.2 Positions
       5.2.3 Input handling
       5.2.4 Updating the view
       5.2.5 Scrolling


The written exam will be online on December 3, 2020, 13:45-15:15 (see instructions). All registered students will receive an email the day before the exam. This email contains 2 links: one for Zoom and one for the exam. The exam link will only work once the exam starts. After you see the exam in your web browser, don't click the link again and don't reload the browser window. Please enter the Zoom session 20 minutes before the exam starts so that we can check the camera settings and your student ID cards.

In order to pass the course, you will have to implement the project as well. The final mark will be computed from the exam (90 points) and from the project (15 points).


Part of the course will be a project in which either a garbage collector, a debugger or a text editor has to be implemented.

The project must be presented via Zoom on January 8, 2021 between 13:00 and 16:00.
In order to minimize waiting times, please login at the following times and have your computer started for the presentation:

   - last names starting with A-A: Mössenböck (
   - last names starting with B-F: Weninger (
   - last names starting with G-I: Mössenböck (
   - last names starting with J-Pi: Weninger (
   - last names starting with Po-Schi: Mössenböck (
   - last names starting with Schm-Z: Weninger (

When you enter the Zoom session you will be put into a waiting room and will be invited to enter the main room when the previous candidate finished.



  • Jones, R., Hosking, A., Moss, E.: The Garbage Collection Handbook. CRC Press, 2012
  • Jones R., Lins R.: Garbage Collection. Algorithms for Automatic Dynamic Memory Management. Wiley, 1996.
  • Levine J.R.: Linkers & Loaders. Morgan Kaufmann, 2000.
  • Rosenberg J.B.: How Debuggers Work. Algorithms, Data Structures, and Architecture. Wiley, 1996.
  • Venners B.: Inside the Java Virtual Machine. McGraw-Hill 1999.

Garbage Collection
  • General
  • Reference counting
    • Collins, G. E: A method for overlapping and erasure of lists. Communications of the ACM 3, 12 (Dec 1960), 655-657
  • Mark & Sweep
    • McCarthy, J.: Recursive functions of symbolic expressions and their computation by machine. Communications of the ACM 3 (1960), 184-195.
    • Schorr, Waite: An efficient machine-independent procedure for garbage collection in various list structures. Communications of the ACM (August 1967), 501-505
  • Stop & Copy
    • Cheney C.J.: A Nonrecursive List Compacting Algorithm. Communications of the ACM, 13(119):677-678, November 1970
  • Generation Scavenging
    • Ungar, D.: Generation scavenging: A nondisruptive high performance storage reclamation algorithm. ACM SIGPLAN Notices 19, 5 (May 1984) and ACM Software Engineering Notes 9, 3 (May 1984).
    • Appel A.W.: Simple Generational Garbage Collection and Fast Allocation. Software Practice and Experience, 1988
    • Ungar, D., Jackson, F.: An adaptive tenuring policy for generation scavengers. ACM Transactions on Programming Languages and Systems 1, 1 (January 1992), 1-27
  • Pointer tables and conservative garbage collection
    • Agesen O., Detlefs D.L.: Finding References in Java Stacks. OOPSLA’97 Garbage Collection and Memory Management Workshop. Atlanta, GA, October 1997.
    • Boehm H.J., Weiser M.: 1988. Garbage collection in an uncooperative environment. Software -- Practice and Experience. 18(9):807-820
    • Diwan A., Moss E., Hudson R.: Compiler Support for Garbage Collection in a Statically Typed Language. Proceedings PLDI'92, p. 273-282, San Francisco, CA, June 1992.
  • Safepoints
  • Miscellaneous
    • Detlefs D., Printezis T.: A Generational Mostly-Concurrent Garbage Collector. Intl. Symp. on Memory Management (ISMM), 2000, 143-154.
    • Deutsch, L P., Bobrow, D. G.: An efficient incremental automatic garbage collector. Communications of the ACM 19,9 (Sept. 1976),522-526.
    • Lieberman, H, Hewitt, C. A real-time garbage collector based on the lifetimes of objects. Communications of the ACM 26, 6 (June 1983), 419-429.
Linkers, Loaders Debuggers Text Editors