5 Root Causes of Legacy Systems


28 March 2024

Legacy Migration

Software Development


The First Steps to Understanding Legacy

Legacy systems often pose significant challenges for organisations, causing frustration and hindering progress. Although they are valuable systems that an organisation wants to keep, they are also difficult to maintain, adapt, and lack the functionality required to support an organisation's growth. If your organisation is struggling to navigate the complexity of software modernisation and maintaining software systems, the first step you need to start with is understanding the underlying root cause of legacy systems. Continue reading to find out the underlying reason why these outdated systems continue to exist and uncover the root causes behind legacy systems.

Top 5 Root Causes

1. Technological Evolution

One of the main causes of legacy systems is the rapid pace of technological advancements. As technology evolves, older systems often struggle to keep up with newer advancements. Without regular updates or continuous modernisation, these systems inevitably turn into failing legacy systems. Newer technologies frequently offer improved performance, scalability, and security features that older systems lack. This widening gap between legacy systems and modern solutions creates significant challenges for organisations. Maintaining and extending legacy software becomes increasingly difficult and costly as the technology gap grows over time.

Moreover, the decreasing support and resources available for older technologies leave organisations relying on legacy systems vulnerable to various risks. These risks includesecurity vulnerabilities, compatibility issues with newer software and hardware, and reduced returns on investment. Consequently, organisations face growing pressures to address the outdated nature of legacy systems and transition towards more up-to-date technological solutions to remain competitive and secure within the changing digital environment.

2. Lack of Documentation

Documentation serves as a crucial resource for understanding and maintaining software systems. However, in many cases, legacy systems suffer from inadequate or outdated documentation. A lack of documentation makes it challenging for developers to comprehend the systems architecture, dependencies, and implementation details. Comprehensive and up-to-date documentation is crucial to create a shared understanding of the inner workings of a software system. Without clear and comprehensive documentation, developers may have to rely on trial-and-error methods to make changes to a system, leading to inefficiencies, errors, and delays. Further to this, as knowledge of the system continues to become lost over time due to turnover, the maintenance burden grows, contributing to the problem of technical debt.

Lack of Documentation is also a main contributor to the root cause of legacy systems. Comprehensive and up-to-date documentation is crucial to create a shared understanding of the inner workings of a software system. Documentation provides insights into the system’s architecture, design decisions, modules, and dependencies, which facilitates maintenance, troubleshooting, and future development. A lack of documentation makes it difficult for developers to comprehend the intricacies of the system, leading to increased maintenance costs, longer development cycles, and a higher likelihood of introducing errors or bugs during maintenance. Software documentation is of similar importance as a vehicle service book. They both serve as valuable records that enhance reliability, support, and create a shared understanding for users, maintainers, and future stakeholders.

Software documentation quote

3. Poor Design & Architecture

The way a software system is designed and built has a big impact on how easy it is to maintain, how flexible it is, and how long it lasts. The design and architecture of a software system are crucial factors influencing its ability to be maintained and to endure over time. If the design and architecture of a system are lacking, it’s more likely for a legacy system to emerge.

Poor architecture within a legacy system is often characterised by disorganised code, a consequence of either inexperienced development or the implementation of overly complex architectures. As a result, this makes the legacy system resistant to specific updates and changes. Changes made to specific features have a ripple effect throughout the entire system, creating a network of dependencies that can make the framework easily breakable and difficult to adapt. These architectural problems make it harder to change parts of the system without causing unexpected issues, making the system even more difficult to maintain.

As the system grows older, it becomes more complex, which makes fixing its architectural problems more expensive. Improving or changing the system's design becomes increasingly challenging and expensive, keeping it stuck in its outdated state, and therefore making it difficult to adapt to new technologies and user needs.

4. Business Changes

As organisations undergo changes, it’s crucial for their software systems to evolve accordingly. However, software systems often struggle to keep up with these transformations. This leads to business changes becoming a fundamental cause of legacy systems and presenting significant operational challenges. When a system fails to align with organisational requirements, it can result in decreased productivity, missed opportunities, and most importantly customer dissatisfaction.

Additionally, as stakeholders’ expectations exceed the capabilities of the legacy system, its perceived value decreases. This can create obstacles to justify ongoing maintenance and improvements to the system, resulting in the system becoming increasingly outdated and disconnected from the organisations key objectives.

To address these challenges, organisations must prioritise continuous modernisation efforts that align software systems with current business objectives. This will bridge the gap between legacy systems and evolving needs, helping organisations to unlock new opportunities such as innovation, efficiency, and growth.

5. Organisational Resistance

Organisational resistance to change plays a significant role in the cause of software legacy systems within organisations. This resistance is driven by factors like established cultural norms, aversion to risk, tight budgets, and conflicting priorities, leading to a reluctance to embrace change.

Despite recognising the limitations of legacy systems, organisations often hesitate to pursue modernisation due to concerns about cost, complexity, and potential disruptions. Additionally, organisational barriers, lack of collaboration, and conflicting agendas among stakeholders worsen the challenge of addressing legacy systems effectively.

This results in organisations becoming stuck in the cycle of making small improvements to a legacy system but are unable to break free from the constraints imposed by organisational resistance to change. These incremental efforts often fail to resolve underlying issues or deliver significant business value, continuing the legacy systems hold on the organisation.


In summary, the root cause of software legacy systems results from a combination of technological, organisational, and architectural factors that accumulate over time. To overcome legacy systems, organisations must focus on modernising these legacy systems and break the cycle of legacy systems through continuous modernisation.

Continuous modernisation is a key strategy for organisations to keep up with changing environments and customer expectations. Read our article for a more in-depth perspective of how continuous modernisation allows the ongoing process of updating and improving systems, processes, and technologies within an organisation to keep pace with changing business needs and market demand.

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