Software Maintenance Costs

Department of Computer Science and Information Systems, University of Jyväskylä

P.O. Box 35, 40014 Jyväskylä, Finland

<URL: http://users.jyu.fi/~koskinen/smcosts.htm>

Sept. 10, 2010

Abstract

Software maintenance and evolution is a considerably understudied area while taking into account its cost effects. This document lists some interesting figures on proportional and absolute maintenance costs, proportions of the main task types, and amount and nature of the existing legacy code. These figures are based on empirical data. Although there has not been much empirical research on this particular area, the magnitude of the maintenance cost effects is clearly identifiable.

1. Proportional software maintenance costs

The relative cost for maintaining software and managing its evolution now represents more than 90% of its total cost. This is refered to as legacy crisis by Seacord et al. (2003). Various studies on this subject are described in Table 1.

Year	Proportion of software maintenance costs	Definition	Reference
2000	>90%	Software cost devoted to system maintenance & evolution / total software costs	Erlikh (2000)
1993	75%	Software maintenance / information system budget (in Fortune 1000 companies)	Eastwood (1993)
1990	>90%	Software cost devoted to system maintenance & evolution / total software costs	Moad (1990)
1990	60-70%	Software maintenance / total management information systems (MIS) operating budgets	Huff (1990)
1988	60-70%	Software maintenance / total management information systems (MIS) operating budgets	Port (1988)
1984	65-75%	Effort spent on software maintenance / total available software engineering effort.	McKee (1984)
1981	>50%	Staff time spent on maintenance / total time (in 487 organizations)	Lientz & Swanson (1981)
1979	67%	Maintenance costs / total software costs	Zelkowitz et al. (1979)

Table 1. Proportional software maintenance costs for its supplier.

2. Absolute software maintenance costs

o Annual software maintenance cost in USA has been estimated to be more than $70 billion (Sutherland, 1995; Edelstein, 1993).

o E.g. in USA, the federal government alone spent about $8.38 billion during a 5-year period to the Y2K-bug corrections.

o At company-level, e.g. Nokia Inc. used about $90 million for preventive Y2K-bug corrections.

3. Maintenance task types

o About 65% of maintenance was found to be perfective by Lientz & Swanson (1981).

o About 75% of maintenance costs are spent for providing enhancements (in the form of adaptive and perfective maintenance) (Martin, 1983; Nosek & Palvia, 1990; van Vliet, 2000).

o Studies of software maintainers have shown that approximately 50% of their time is spent in the process of understanding the code that they are to maintain (Fjeldstad & Hamlen, 1983; Standish, 1984).

4. Legacy code amount

o In 1990 there were an estimated 120 billion lines of source code being maintained (Ulrich, 1990).

o In 2000 there are already about 250 billion lines of source code being maintained, and that number is increasing (Sommerville, 2000).

o An average Fortune 100 company maintains 35 million lines of code (Müller et al., 1994).

o These companies add in average 10% each year only in enhancements (Müller et al., 1994).

o As a result, the amount of code maintained doubles in size every 7 years (Müller et al., 1994).

o Older languages are not dead. E.g. 70% or more of the still active business applications are written in COBOL (Giga Information Group).

o There are at least 200 billion lines of COBOL-code still existing in mainframe computers alone (Gartner Group).

References

1) Eastwood, A. (1993). "Firm fires shots at legacy systems". Computing Canada 19 (2), p. 17.

2) Edelstein, D. (1993). "Report on the IEEE STD 1219 – 1993 – Standard for Software Maintenance". ACM SIGSOFT Software Engineering Notes 18 (4), p. 94.

3) Erlikh, L. (2000). "Leveraging legacy system dollars for E-business". (IEEE) IT Pro, May/June 2000, 17-23.

4) Fjeldstad, R. & Hamlen, W. (1983). "Application program maintenance-report to to our respondents". Tutorial on Software Maintenance, 13-27. Parikh, G. & Zvegintzov, N. (Eds.). IEEE Computer Soc. Press.

5) Huff, S. (1990). "Information systems maintenance". The Business Quarterly 55, 30-32.

6) Lientz, B.P. & Swanson, E. (1980). "Software Maintenance Management: A Study of the Maintenance of Computer Application Software in 487 Data Processing Organizations". Addison-Wesley: Reading, MA, 214 p.

7) Lientz, B.P. & Swanson, E. (1981). "Problems in application software maintenance". Communications of the ACM 24 (11), 763-769.

8) Martin, J. (1983). "Software Maintenance: The Problem and Its Solution". Prentice Hall, 472 p.

9) McKee, J. (1984). "Maintenance as a function of design". Proceedings of the AFIPS National Computer Conference, 187-193.

10) Moad, J. (1990). "Maintaining the competitive edge". Datamation 61-62, 64, 66.

11) Müller, H., Wong, K. & Tilley, S. (1994). "Understanding software systems using reverse engineering technology". The 62nd Congress of L’Association Canadienne Francaise pour l’Avancement des Sciences Proceedings (ACFAS), 26 (4), 41-48.

12) Nosek, J. & Palvia, P. (1990). "Software maintenance management: changes in the last decade". Journal of Software Maintenance: Research and Practice 2 (3), 157-174.

13) Port, O. (1988). "The software trap – automate or else". Business Week 3051 (9), 142-154.

14) Seacord, R., Plakosh, D. & Lewis, G. (2003). "Modernizing Legacy Systems: Software Technologies, Engineering Processes, and Business Practices" (SEI Series in Software Engineering). Addison-Wesley.

15) Sommerville, I. (2000). "Software Engineering (6th Edition)". Addison-Wesley.

16) Standish, T. (1984). "An essay on software reuse". IEEE Transactions on Software Engineering SE-10 (5), 494-497.

17) Sutherland, J. (1995). "Business objects in corporate information systems". ACM Computing Surveys 27 (2), 274-276.

18) Ulrich, W. (1990). "The evolutionary growth of software engineering and the decade ahead". American Programmer 3 (10), 12-20.

19) van Vliet, H. (2000). "Software Engineering: Principles and Practice". Wiley.

20) Zelkowitz, M., Shaw, A. & Gannon, J. (1979). "Principles of Software Engineering and Design". Prentice-Hall.

Updated: Sept. 10, 2010 by Jussi Koskinen.