Modernising Software 101


14 February 2024

Software Development

Legacy Migration


A common question we get asked at WorkingMouse is “How do I know if I'm using a legacy system?”

At some point, you’ve probably used a legacy system without realising. Legacy Systems have red flags such as;

  • Frequent down time
  • Poor user experience
  • Outdated technology stack
  • High maintenance costs
  • Lack of support
  • Lack of security

Legacy systems are valuable systems that an organisation wants to keep, despite the challenges it presents due to their complexity. They are often referred to as a business’s biggest asset whilst also being the businesses biggest liability.

Legacy Systems

Legacy Systems are hard to comprehend due to their complexity, making it difficult to maintain, adapt, deploy, and lacks functionalities necessary to support an organisations growth. Most of these systems were developed before modern software engineering methods became widely used and have been maintained to adjust to changing requirements over time. Additionally, since the original designers and developers have most likely left the organisation, there is limited people that can provide explanations about the functionality. Additionally, the cost of operating a legacy system is often deemed unjustifiable. Legacy systems must evolve to address changing needs as business requirements evolve over time.

Replace vs Modernise

A legacy system can progress through three avenues: maintenance, modernisation, or replacement. At some stage, the existing system will reach a point where further evolution is no longer possible, it then requires either replacement or modernisation. Replacing a system involves building or purchasing a new system to replace the outdated legacy system, often requiring significant investment. One downside to replacing a system is the new system may not fully meet the organisations requirements, leading to the necessity of customisation. Further to this, most legacy systems are often custom to suit specific needs, replacing the system entirely may not always be possible.

The other avenue is modernisation, involving restructuring the legacy system using modern programming languages, such as object-oriented programming (such as Java, C+, Python, and C#), while reusing existing assets. This process aims to improve reliability and maintainability, updating outdated applications and connecting them with newer technologies. This avenue focuses on retaining and extending the value of the existing investment through migration to new platforms. Modernisation projects are most suitable to organisations who have legacy systems that are low quality but provide high business value.

Why Systems need Modernising?

Software systems are constantly evolving. For example, the average Fortune 100 company maintains 35 million lines of code and adds 10% each year just in enhancements, updates, and maintenance. Consequently, the codebase of these companies doubles in size every 7 years, resulting in more technical debt and prompting the need for upgrading or modernisation.

The most common reasons for modernising legacy systems include increased maintenance costs, reduced productivity, limited user access, poor documentation, integration issues, and outdated hardware and software. Maintaining a legacy environment can consume a large percentage of an organisations budget and human resources. On average, organisations may spend from 60-85% of software development budget on maintaining legacy systems that fail to meet evolving business needs. Due to these challenges, organisations often look into adopting new technologies and architectures to modernise their legacy systems. To read more about the challenges and top risks of software modernisation, refer to our blog here.

Wrapping up...

Modernising a legacy system should focus on keeping its business value intact and ensuring the system is easy to maintain. This is because organisations want to get the most of their existing investments from their legacy systems. As organisations face increasing pressure to reduce costs and respond more efficiently to ongoing business demands, the importance of modernising legacy systems becomes more evident. This need can be driven by market dynamics, business requirements, and advancements in technology.

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Jessica Montgomery

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