What Is a Legacy Application?

Legacy applications are older software systems that remain critical to business operations, even though they may no longer be actively maintained or updated.

A legacy application is an older software program or system that continues to be used within an organization, often due to its importance to core business operations, despite being built on outdated technologies or architectures. These applications were typically developed years, sometimes even decades ago, and may rely on outdated programming languages, operating systems, or hardware.

As a result, they often lack modern features, such as enhanced security, scalability, and interoperability, which makes them challenging to integrate with contemporary systems. Legacy applications may also have limited support from their original developers or vendors, leading to difficulties in maintenance and adaptation to current business needs.

Despite these challenges, organizations continue to rely on legacy applications due to the essential data and processes they support, and the potentially high cost or risk associated with replacing or reengineering them.

Types of Legacy Applications

Here are the common types of legacy applications.

Mainframe Applications

Mainframe applications are often mission-critical systems running on mainframe computers, typically used by large organizations for high-volume transaction processing, like in finance, insurance, and government sectors. These applications are stable, highly reliable, and secure but are based on older programming languages like COBOL and can be expensive to maintain and difficult to integrate with modern technologies.

Desktop Applications

Desktop applications are standalone programs installed on individual computers rather than a centralized server. These legacy systems may lack cloud capabilities and are often limited in terms of collaborative functionality, making remote access and cross-device compatibility a challenge. Updating these applications usually requires manual installation on each machine, which can be time-consuming and resource intensive.

Custom-Built Applications

Many organizations have custom-built applications tailored to their specific business needs. While these applications can be highly specialized and valuable, they’re often based on older programming languages and frameworks that can be challenging to update or migrate. Maintenance can be costly, especially if the original developers are no longer available, as newer development teams may struggle with the outdated codebase and lack of documentation.

Enterprise Resource Planning (ERP) Systems

Legacy ERP systems, often implemented many years ago, manage critical business processes such as inventory, finance, and human resources. Although these applications provide a stable environment for operations, they’re typically monolithic and difficult to customize or expand. Integrating them with newer systems can be challenging due to rigid data structures and limited API support, which restricts the ability to leverage cloud solutions or other modern technologies.

Database Management Systems (DBMS)

Older database management systems store large volumes of critical organizational data and are often central to legacy application infrastructure. These systems may be based on outdated architectures, which can affect performance, scalability, and security. Migrating to a modern database structure is complex, particularly if the DBMS has become tightly integrated with other legacy systems over time.

Web-Based Legacy Applications

Early-generation web-based applications, developed with outdated web technologies, are another type of legacy system. While initially designed to bring some level of accessibility via the internet, they often rely on technologies like old Java applets or Flash, which are no longer supported in modern browsers. These applications may have limited responsive design, security vulnerabilities, and outdated user interfaces that impact user experience and compatibility with modern devices.

Supply Chain Management (SCM) Systems

Legacy SCM systems coordinate the production, shipping, and distribution processes within a company. While these systems are essential for logistics and supply chain visibility, they often lack flexibility and are challenging to update or customize. Modernizing SCM systems typically involves migrating data and workflows to more adaptable, cloud-based systems that can better accommodate today’s complex, dynamic supply chains.

Legacy Applications Examples

Legacy applications are essential but outdated systems that organizations rely on to support key business functions. Here are a few notable examples:

COBOL-Based Banking Systems. Many banks and financial institutions still rely on COBOL-based applications for processing transactions and managing customer accounts. Developed in the 1960s and 1970s, these applications are highly reliable but challenging to maintain, especially as COBOL expertise becomes increasingly rare. Replacing these systems can be risky and costly, which is why they often remain in use.
Microsoft Access Databases. Microsoft Access, a desktop-based database application, has been widely used for small-scale data storage and simple applications within departments. While it provided flexibility for non-developers to create their own solutions, Access is limited in scalability and is difficult to integrate with modern, cloud-based databases, making it a common legacy application that many organizations are working to phase out.
Lotus Notes. Lotus Notes (now IBM Notes) was once a popular platform for email, collaboration, and business applications, especially during the 1990s. While it offered a wide range of features, Lotus Notes has become outdated compared to modern, cloud-based collaboration tools. Many organizations still rely on it due to the critical business data it holds, and because it’s often complex and costly to transition away from.
Oracle Forms and Reports. Oracle Forms and Reports is a development and deployment tool for creating data-driven applications, widely used in the 1990s and early 2000s. Although powerful, it has since become a legacy platform with limitations in user experience, and it can be difficult to integrate with modern web technologies. Organizations are gradually moving away from it, but the complexity of migrating forms and reports keeps it in place for many.
AS/400 Systems (IBM iSeries). AS/400, later rebranded as IBM iSeries, is a family of midrange computers used primarily in manufacturing, logistics, and finance sectors. These systems are highly robust and have been in use for decades, managing critical applications. However, AS/400 runs on proprietary IBM technology, making it difficult to integrate with modern software and expensive to maintain as the number of specialists decreases.

What Is Legacy Application Modernization?

Legacy application modernization is the process of updating or transforming outdated software systems to align with current technology, business needs, and user expectations. This process often involves enhancing or reengineering legacy applications to improve their functionality, scalability, security, and integration capabilities. By modernizing legacy applications, organizations reduce technical debt, lower maintenance costs, and mitigate risks associated with relying on outdated technologies.

Modernization can take many forms, from rehosting or migrating applications to cloud environments to rearchitecting them to leverage microservices, containers, or serverless computing. Other modernization strategies include rewriting portions of the code, replacing legacy applications with newer software, or integrating them with modern APIs to extend their functionality.

The ultimate goal of legacy application modernization is to retain the business value of these applications while ensuring they are compatible with modern infrastructure, easier to maintain, and capable of evolving alongside technological advancements.

Benefits of Using Legacy Applications

Despite their outdated nature, legacy applications offer several benefits that can make them valuable for organizations:

Reliability and stability. Legacy applications are typically highly reliable and stable, as they have been used over many years and refined through continuous updates and fixes. Organizations depend on them for critical functions because these systems are less likely to experience unexpected failures, which is essential for high-stakes industries like banking, healthcare, and government.
Cost savings. Using existing legacy applications can save costs compared to building or purchasing new software. These applications are already integrated into the organization’s workflows, reducing the need for new infrastructure, training, or custom development. Replacing them often requires significant investments, which companies may prefer to avoid if the legacy system still meets essential needs.
Embedded business logic. Legacy applications often contain complex and refined business logic, processes, and workflows that have been developed and customized over years to suit specific business needs. Reproducing this in new systems can be challenging and costly, as newer applications may lack the specialized functionality that legacy systems provide.
Data retention and accessibility. Legacy systems often hold large volumes of historical data crucial to the organization. This data may include customer records, transaction histories, or compliance-related information. Accessing this information in its original system allows the organization to easily retrieve past records and comply with regulatory requirements.
User familiarity. Employees who have used legacy systems over the years are familiar with the interface and workflow, which can improve efficiency and reduce the learning curve compared to new applications. This familiarity also minimizes disruption to daily operations, as employees can continue to work without extensive retraining.
Lower security risks (in some cases). Although many legacy systems are vulnerable to modern cyber threats, certain legacy systems disconnected from the internet or operating in a closed environment can have lower exposure to security risks. This isolation can make them harder to breach compared to modern, network-connected applications.
Reduced downtime. Because legacy systems have been in operation for years and often undergo fewer updates, they typically experience lower downtime than newer applications that require frequent patches or upgrades. This is advantageous for critical business operations where continuous availability is essential.

Challenges of Using Legacy Applications

Here are some common challenges of using legacy applications:

Technical debt accumulation. Legacy applications contribute to technical debt as they continue to use outdated code, making it more difficult and costly to maintain and expand. Over time, this technical debt becomes a major barrier to innovation, as resources are devoted to managing the legacy system instead of investing in new, value-added projects.
High maintenance costs. Legacy applications often require specialized knowledge and resources to maintain, as they rely on outdated technologies and languages. The scarcity of skilled professionals for these older systems drives up costs, making maintenance an expensive and resource-intensive process.
Security vulnerabilities. Older applications are more susceptible to security vulnerabilities, as they may not have been designed with today’s security standards in mind. Lack of vendor support and updates makes it difficult to patch known vulnerabilities, exposing organizations to cyber threats and data breaches.
Limited scalability. Legacy systems are typically designed to operate on specific hardware or within certain performance parameters, making it difficult to scale them in line with modern requirements.
Incompatibility with modern systems. Legacy applications often lack the flexibility to integrate with contemporary systems or cloud-based solutions. This incompatibility creates data silos, reduces operational efficiency, and complicates workflows, as organizations may need to develop costly workarounds or custom connectors.
Poor user experience. Many legacy applications have outdated interfaces and limited functionality compared to modern solutions. These interfaces can be difficult to navigate, impacting productivity and increasing the learning curve for new employees.
Data silos. Legacy systems often store data in closed-off or proprietary formats, creating isolated data repositories that make it challenging to extract, share, or analyze data across the organization.
Reliability and performance issues. As legacy applications age, they tend to suffer from reliability and performance degradation, often requiring more frequent repairs and downtime.
Vendor and support limitations. Many legacy applications are no longer supported by the original vendors, meaning updates, security patches, and technical support are either limited or unavailable. Organizations using unsupported software face increased risks and challenges in maintaining and troubleshooting these systems.