Old system or contaminated site: How can legacy systems be modernized?

After decades of use, many of the systems that once formed the core of the company are out of date. With the continuous further development of technology, the question arises which programs can keep up and which cannot. The latter are legacy systems and are carried along until they can or must be replaced. You can now find out which solutions are suitable for high-level programming languages.

What are legacy systems exactly?

Legacy systems are old systems that, due to their core functionality, can only be renewed with great effort. The English word “legacy” can be translated not only as “inheritance” or “legacy”, but also derogatory as “legacy” or “legacy”. Another interpretation is “legacy” and “legacy”, with an emphasis on content that is definitely worth keeping. In particular, high-level programming languages such as PL / 1, Fortran, COBOL and Natural are deeply rooted in the IT infrastructure and cannot simply be erased.

Areas of application of legacy software

These established legacy systems are common in banks, insurance companies and other economic sectors. They still have enormous economic potential. The best example is the European banking system, which is still running with very outdated legacy software. The traditional system supports the entire company, with company-specific knowledge and individual business logic. This makes them a unique selling point for the company. These systems are therefore of crucial importance, have mature core functions and work reliably during operation. On the other hand, legacy software is characterized by outdated data management, bulky user interfaces and old programming languages that do not meet modern requirements. In many cases it can be replaced by a modern and cost-saving architecture.

COBOL is used, for example, in the formulation of business rules. The main area of application is business data processing. PL / 1 is mainly used on IBM mainframes, but there are also variants for Windows, AIX and other UNIX variants. Fortran is the focus where there is a lot to calculate, such as in physics and engineering. Natural is used for commercial application programs and was originally developed for mainframes from Siemens and IBM. Regularly changing business processes undermine these programming languages and increase maintenance costs. The original user of the system is about to retire and it is difficult to find young people interested in these historical techniques. In this narrow field, companies are increasingly choosing to replace their old software.

Legacy system risk: There are numerous reasons why legacy systems should be replaced:

Hardly any access

Just a few years ago, there was little understanding of IT architecture. As a result, only a few applications could automatically access the legacy system from outside or inside in the past. In recent years, the provision of interfaces to other systems has increasingly become a basic function.

Compliance issues and regulatory requirements

The outdated data processing is problematic with regard to inspection and software documentation within the meaning of the GDPR and other data protection regulations. In many legacy systems, the requirements that data can be identified, extracted or deleted easily, quickly and directly are not taken into account.

Opaque data silos

Not only the system documentation, but also the data management within the legacy system is a challenge. In the age of artificial intelligence, data science and data analysis methods, it is important to extract information from the system as easily as possible and make it available centrally. In legacy systems, difficult data models and opaque databases hinder this work.

Complicated maintenance work

Both the maintenance costs and the workload of the legacy system are higher than those of a modern architecture. In extreme cases, there is neither manufacturer support nor employees who are familiar with the software. It takes a lot of time to keep these systems running. Modernization can solve this problem.


A particular problem with legacy systems is that the security protection is getting weaker and weaker. Current software vendors provide security updates and are constantly making bug fixes, while legacy systems don’t get this basic maintenance. This obstacle is reflected in infrastructure weaknesses that need to be addressed as soon as possible.

High costs

One of the main problems with legacy systems is the cost of infrastructure and maintenance. The operation of the legacy system leads to running costs that are continuously increasing due to outdated technology. Outdated infrastructures, code bases and programming languages such as COBOL, PL / 1, Natural and Fortran require special expertise just to maintain the status quo. This special investment is quickly reflected in the operating costs.

Lack of integration due to outdated programming languages

In addition to increasing maintenance costs, the integration of legacy systems is also a problem. A few years ago it was not important to combine systems and integrate them into IT architectures. But this is the case today. The lack of integration options for legacy systems sparked ideas for further development and cross-linking.

These challenges arise with the further development / replacement of legacy systems

Legacy systems had their raison d’etre. Due to technological progress and constantly increasing requirements, it is usually no longer sensible to continue operating the systems. However, the transfer is not easy for the following reasons:

  1. Effort: Obsolete systems are written in old programming languages that are no longer used or poorly documented. Installing an interface for a new migration system is complicated. It is even more difficult to equip employees with the appropriate knowledge.
  2. Integration: Traditional systems are usually core systems that are deeply integrated into the IT architecture. Replacing these requires very careful planning.
  3. Change of a running system: Even when the benefits are clearly defined, companies are often reluctant to replace working software. Employees are the main delay factor here, as they are used to the legacy system.
  4. Exchange: Traditional systems are usually designed as independent systems. As a result, a full replacement process is applied instead of updating key components like in the microservices domain.
  5. Costs: Legacy systems consume a lot of resources. A change between the two systems and the temporary double operation of the two systems also cause costs.

How do you solve these challenges?

There are many reasons for replacing outdated software and hardware. The old system is renewed through data migration, temporary replacement, outsourcing of some functions or parallel operations. There are two sources of error to avoid: functional errors and data loss.

Data migration to avoid data loss

One of the worst situations in replacing an old system is data loss. Since new data models are seldom designed like old systems, data transfer must always be carefully planned. The solution is strategic data migration. For this purpose, data is extracted from the old system and transferred to the new system during the exchange. During this data migration, care must be taken not to lose data. This migration must take place in parallel with the online operation of the new system or afterwards. Depending on the database, the data transfer can either take place later or the operation of the system must be suspended.

Temporary replacement of the old system

There are basically three options for directly replacing the old system. The new models cover all functions. The new system only gradually switches over some functions or initially carries out parallel operations, which enable continuous checking in both systems. The most effective way to replace legacy software is to prepare a new system and replace the old one after the data migration.

Then all operations are carried out directly on the new system, data is created in the new system and all users must use the new software directly. The disadvantages are obvious: if something doesn’t work, important components in the IT infrastructure are paralyzed, the need for special training is very high, and if the exchange fails, data loss is inevitable. Instead, there is a method of continually replacing legacy systems based on functionality. For this reason, both systems are in a real-time switching state and components are only migrated gradually. In this way, the function can be checked continuously, while the effects in the event of a fault are kept as low as possible.

Sometimes functional methods increase the reliability of success, but also increase the need for care and organization. In general, this increases the duration of the project as each individual component is checked. It is also necessary to precisely control the coordination of employees so that it is clear which component is used in which system. According to this principle, it is necessary to create an interface to the old system so that (similar to a microservice architecture) data can be exchanged between systems. This need increases the preparatory work.

Temporary parallel operation

Another established method for migrating older systems is to temporarily fully operate both systems. With this solution, two complete systems have to be maintained and operated at the same time. The advantages are obvious: it soon becomes clear whether the two systems achieve the same results, store the same data and perform the same. In general, however, this parallel operation cannot be maintained for long because it is very cumbersome.

Modernize legacy systems: What does “reverse engineering” mean?

Reverse engineering refers to the reconstruction of an existing product – in this case software. In order to understand the structure and function of the program, it is broken down during reverse engineering and system documentation is created by the existing system. The purpose of software reverse engineering is to recreate the code of an existing program. In this way it is possible to optimize the software, correct functional errors, analyze competing programs and develop new systems.

If you need support with the software documentation of legacy software, contact us and we will arrange a non-binding appointment!

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