Software DevelopmentBuilding Software For Legacy Systems

Building Software For Legacy Systems

Legacy systems can be described as hardware or software that are old but are still being used. These systems are generally less efficient and have fewer functionalities than newer ones but are still operational. However, legacy systems are not necessarily old systems but they simply might not be able to meet the current requirements or might have a lack of support.

They might also have the inability to be integrated with other systems and platforms. Outdated architecture, platforms, designs or technology are harder to maintain and are more expensive to fix. Due to this, these devices and software become a barrier to digitization or advanced digital transformation.

DOS software is an example of Legacy systems as the last Windows Operating System to run on DOS was Windows 98. Other Windows versions such as XP, Vista, and 7 have compatible drivers and migration is possible across some older systems as well, however, when it comes to DOS systems and extremely old hardware (less than the required processing power or Random Access Memory), it becomes challenging.

Many organizations or corporations still use these systems, due to not wanting to migrate their business activities to a newer IT setup. For example, a food chain might not wish to upgrade its systems, and the company might keep running old billing and inventory software as it gets the job done for them. However, by not upgrading legacy systems, organizations may fall victim to frequent crashes and data loss. Thus, it is crucial to if not change legacy systems, then, at least optimize or upgrade them with updates or modifications. 

Optimization or Modernisation of Legacy Software

Businesses change with time and serve more customers or users, thus, working with more data than before. It is absolutely essential for existing systems to adapt to this in order to function effectively. Legacy systems such as computers running MS-DOS or Windows 98 are slow and software such as Microsoft Word 2001 is less efficient than the newer 2019 or 2020 versions, so it is always better to upgrade to the newer versions. However, when it comes to dedicated hardware or personalized software that businesses have bought or acquired and are using across a large number of computer systems, it is sometimes hard to simply shift to newer technologies. When it comes to a large number of systems, migration might be costly, thus, sometimes it is better to optimize existing systems or get software built for legacy hardware.

Here are some ways we can optimize or modernise legacy software:

    • Encapsulation: Encapsulation helps in leveraging the software for extending its value and features. While retaining the code in the legacy environment, components can be used to connect to other systems through an API. 
  • Rehosting: Rehosting is the process of migrating the mainframe software to another offline or cloud infrastructure. It can even be a virtual environment. This helps in speeding up business processes while the underlying business logic of the program remains unchanged.
    • Replatform: This is similar to rehosting but with additional adjustment of code for up-versioning the software. This makes the legacy software suitable for new platforms and makes the program scalable. This helps in using cloud functionalities, thus offering cost optimization and more efficient use of computing resources.
  • Code refactoring: If code can be optimized and restructured without changing the external behavior of the software, one can refactor software components to solve errors or make adjustments to the features and structure of the program.
  • Rearchitecting: This involves shifting to new software architectures with the alteration of code for fully utilizing the performance capabilities of a new platform. This is a highly code-intrusive process and must only be done if backward compatibility is possible. 

Here are some challenges one might face when working on legacy systems:

  • Limited innovation: It is difficult to integrate modern solutions with legacy applications in a natural manner.
  • Dedicated Pipeline: There must be a separate pipeline and separated associated processes for mainframe development.
  • Slow Testing: Testing is limited for legacy systems as there is a lack of automation and autonomy solutions for testing.
  • Manual Segregation of Components: Components cannot be visualised in an automated fashion and isolating components is harder as older system designs were not compartmentalised and were heavily dependent on other strings, thus, making the whole program crash if changes are made. Thus, one needs to encapsulate the program first.

Development of Software for Legacy Systems

More often than not, it is better to build better software from scratch to replace older legacy systems than to try optimising it. For software that is being built for legacy systems, existing business logic (if any) must be rewritten and packages must be customised or reengineered. One can also choose to redesign existing applications for increasing the functionality or the capabilities of the program. While developing software for these legacy systems or on legacy systems, one must also try understanding the scope for integration and how to extend its features through modern technology or other third-party platforms.

When building software for legacy hardware, one cannot go beyond what the hardware can support and must use virtual environments that will simulate the outdated hardware in order to check how the program runs and under what conditions. For example, too much pressure on the processor or a case of overheating must be avoided, thus benchmarks must also be strategised for creating a compatible software for legacy hardware.

Issues Faced with Legacy Systems

There are many reasons why one needs to upgrade or repurpose legacy systems, here are some of them:

  • Maintaining legacy systems is costly.
  • Legacy systems create byproducts such as data silos that create integration problems.
  • It is harder to adhere to modern compliance regulations due to these systems being outdated and not meeting the compliance requirements.
  • There is a huge security risk and a high probability of data or system breaches.
  • It is harder to recover or backup legacy systems and the data generated by them.


When it comes to hardware, if a company does not wish to change a massive batch of computer systems that have older hardware, they can get custom software developed that will function with those specifications. Similarly, for older Operating Systems, one can ask for basic software to also be built.

Also Read: Best b2b eCommerce software solutions 2022


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