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What is a Mainframe?

What is a mainframe


Mainframes were the large cabinets housing the central processing unit (CPU) and main memory of early computers. The term persists to describe and differentiate these larger computers, known for their considerable size and amount of storage, processing power, and reliability, from smaller counterparts such as servers, minicomputers, workstations, and personal computers (PCs). While mainframe is a generic term, most people instantly associate these computing workhorses with IBM and their System Z, the most popular and widely used models. The Z15 is the latest model.

The Modern Mainframe – Automated, Protect, Connected.

IDC research shows that traditional host platforms are well suited to play a pivotal role in digital transformation. This white paper looks at application access and security, RPA benefits, as well as host system security hurdles and how best to overcome those modernization challenges.

Download the report


How do mainframes help large organizations?

Despite advances in technology, mainframe-hosted systems remain business-critical, and at the heart of enterprise computing. Nothing else matches their levels of performance, consistency, and reliability.

As systems of record they hold and protect the complex, transactional and operational rules and policies that define an organization. Most mainframes can run multiple operating systems, handle high-volume input and output (I/O), and add or hot swap system capacity, without disruption to the business. A single mainframe can replace dozens, or even hundreds of smaller servers, whereas the reverse would be difficult to achieve with the same levels of reliability.

Why do enterprises still use mainframes?

One answer is that mainframes are better at what they do than any other platform. Another is the mainframe is so deeply embedded into the organizational IT that extracting and replacing these core systems, often written in COBOL, carries more risk than potential reward. However, there is another way, as we shall discover. So entrenched is this corporate “big iron” that IBM notes that 80 percent of the world’s corporate data resides or originates on mainframes.

Despite game-changing advances elsewhere in corporate IT, many organizations still rely on their most dependable business platform (the mainframe) to run their most important applications. As the organization evolves, the key is to bridge the gap between the old-school reliability, current business need, and the future innovation customers will demand.

We call this requirement mainframe modernization. This is a broad term and includes a range of potential activities, all ultimately aiming at improving business results by improving existing mainframe-based IT services.

Why modernize the mainframe?

Modernization fundamentally aims to take what is already working, and improve upon it to achieve new business outcomes. And realistically, because mainframes are inseparable from many organization’s business-critical systems and applications, they should underpin any modernization strategy.

As IDC observes, “Modernizing investments in core mainframe and other existing systems for [digital transformation and innovation is vital across applications, process strategies, and infrastructure.”

Successful mainframe modernization leverages and extends the value of core system investments, such as applications, processes, and infrastructure. Companies with so-called legacy (old-but-gold) systems must enhance their ability to deliver innovation, efficiency, and security – all without compromising their business-as-usual work – are ideal modernization candidates.

IDC InfoBrief, sponsored by Micro Focus (now part of OpenText™), Modernization Strategies as a Foundation for Digital Transformation, April 2020

What can mainframe modernization achieve?

Typical mainframe modernization goals include:

  • Supporting new markets and services to address competitive challenges and device variety.
  • Revitalizing and broadening mainframe application assets.
  • Integrating with new technology using REST/JSON, API, micro services or .Net and Java frameworks.
  • Supporting new cost models, on-premises and/or cloud (or hybrid).
  • Providing options for flexibility, data security, and access.

What are the options for mainframe modernization?


The least aggressive and most logical way to take legacy systems into the future is to harness the power of software that bridges the old and new to extend the capabilities of current technologies and investments.

We call this modernization, and this strategy is gaining more traction with analysts. As IDC states, “Modernizing investments in core mainframe and other existing systems for DX and innovation is vital across applications, process strategies, and infrastructure.” Organizations embracing smart DX optimize savings by maximizing ROI on IT investments, and reduce their risk profile by maintaining tried-and-trusted processes.

Modernizing a mainframe could encompass a range of options –

  • Application modernization, which relates more to software than hardware. “AppMod” also applies to distributed, off-the-mainframe platforms as much as the mainframe itself, but many of the world’s most important back-end applications (often called systems of record) reside on mainframes.
  • Process modernization, which in the context of mainframes will focus on using DevOps practices and tools to improve and secure user access, boost new platform integration, and accelerate deployment.
  • Infrastructure modernization, which may involve looking at the platform itself and potentially exploring additional elements such as the cloud to provide a more flexible IT deployment environment.

Rip and replace:

This comes from our digital transformation guide.

“For [those] with core business systems that have been in place for many years, the prudent approach is typically to build on to what already exists. A rip-and-replace strategy introduces strategically unacceptable levels of risk, plus negatively impacts cost and time-to-market.”

This IDC InfoBrief also notes that the best practice is to modernize “existing application assets to preserve/enhance existing investments (avoiding risky “rip and replace” projects)”.

Why do mainframes remain popular with banks and big finance?

Two words: power and reliability. Both are essential to any organization processing big numbers. Only mainframes have the necessary power to support the multiple IT functions banks demand. From the unseen, such as overnight batch runs, to providing back office support for mobile banking apps, the mainframe does both the heavy lifting banks need with the technology-forward integrations consumers expect.

The mainframe is the single platform answering multiple challenges. They are the systems of record, the number crunchers, the power behind cloud and mobile transactions. Mainframes monitor processes for fraud, perform real-time analytics, and many more functions – and all simultaneously.

Does the mainframe have a future?

In 1994, the growing computing power of PCs prompted American IT journalist Stewart Alsop, Jr. to predict the last mainframe would be unplugged by March 1996. In 2002, he ate his words. Mainframe computing power has grown 30 percent annually since 1992 and they have been adapted to thrive and survive in the IT jungle.

2019 COBOL Survey revealed that 70 percent of enterprises plan to keep their mainframes, and modernize key COBOL applications instead of replacing or retiring them. Additionally, 92 percent of respondents felt their COBOL applications were strategic – up from 84 percent in 2017. So, the short answer is yes.

How do I access the mainframe from the cloud?

BMC’s 2019 Mainframe Market Survey confirmed the viability of mainframes, and that 45 percent of enterprises regarded cloud technology implementation as a priority. Leveraging the private or public cloud helps increase availability, scalability, and performance, improve security, and reduce mainframe application costs. Key to this is centrally managed, browser-based access. It enables swift end-user configuration, deployment, updates, and terminal emulation functionality.

Browser-based host access, using an identity access management (IAM) system rather than eight-character passwords, will authorize or deny mainframe access by leveraging enterprise authentication credentials. This ensures users only access the mainframe systems and data they need, using the principle of least privilege. Zero-footprint host access enables essential, secure mainframe access either on premises or in the cloud, without having to manage each desktop, or rely on other systems (like Java) or vendors (like Oracle).

How can I migrate the mainframe to the cloud?

Moving applications and data from any platform to another – whether platform change or infrastructure modernization – is a technical project demanding careful planning. To learn more about mainframe migration and modernization, check out our modernization brochure or the dedicated “What is App Modernization?” page.

Although off-cloud or on-prem environments remains popular platforms for mainframe application workloads, cloud has become the new destination for IT leaders.

For many, this digital transformation of mainframe COBOL and PL/I applications is a step-by-step journey which takes place over time. Whether Cloud is your final destination or if you’re unsure, but seeking new approaches for application modernization, there are many resources available to support your plan. At OpenText, we see that modernization journey to the cloud in three 3 steps:

  • Get Cloud Ready: Plan using code analysis tools. Move to commodity x86 hardware platforms. Adopt Agile and containerization for more reliable and faster application delivery.
  • Migrate and Optimize: Quickly extend application value into the cloud using virtualized, containerized and cloud platforms. Adopt DevOps and managed services (XaaS) such as databases, analytics, and storage.
  • Go Cloud Native: Embrace cloud-native architectures and reach higher levels of performance and reliability at lower cost. Deliver new business value faster by implementing DevSecOps and API-enabling applications.

For those interested in getting started and mapping their Destination Cloud strategy, explore this resource page for more information.

How does RPA work with the mainframe?

Sometimes referred to as software robotics, robotic process automation (RPA) is the technology some organizations use to automate business processes. ”Robotics” refers to metaphorical software robots, or genuine artificial intelligence (AI).

Most organizations retain the most valuable asset, their business data, on the mainframe (80 percent of the world’s corporate data resides on mainframes). Using RPA initiatives, enterprises can leverage this unique information to increase productivity, reduce errors, and improve customer service. They use one of two methods to integrate RPA – either using web services or the more traditional Application Programming Interfaces (APIs), such as HLLAPI, or .NET.

There are many options for enabling the integration of mainframe-hosted data (often known as “3270/5250”, in reference to IBM model numbers) for enterprise RPA initiatives.

Service-enabling the mainframe (or host), is a scalable approach to RPA. It requires developing distinct procedures against host-based applications performing defined units of work as consumable web services for the RPA tool to call on as needed in an automated process.

The access standard for more than 30 years, IBM’s High Level Language Application Program Interface, or HLLAPI, is the traditional automation interface for mainframe green-screen data. In this scenario, the RPA tool accesses host data by leveraging HLLAPI through a terminal emulator and corresponding green screen. All RPA solutions support this standard interface for mainframe data access.

OpenText Host Connectivity solutions include this data via a desktop-based terminal emulator. For HLLAPI-savvy organizations, this can be a faster way to leverage mainframe data in an RPA-based automated process.

How do I automate terminal-based mainframe application testing?

Test automation works on at least two levels for organizations. First, it can increase the delivery velocity of terminal-based mainframe applications. Secondly, it meets user requirements without compromising quality; or as the industry prefers to describe it, automated terminal-based mainframe application testing establishes a continuous integration/continuous delivery (CI/CD) pipeline.

By automating testing behind CI/CD practices, mainframe development teams can meet both user and line-of-business (LOB) demands quickly and efficiently. Organizations using functionalregression, and performance testing – solutions all covered within our ADM portfolio – are equipped to deliver mainframe applications that meet regulatory requirements on time, with fewer bugs, and increased scale and flexibility.

There are solutions in the marketplace that deliver automated testing that work with current testing solutions and infrastructure, using discrete services to automate terminal-based mainframe application testing. These services use encapsulated application business logic that is exposed by many standard interfaces.

Securing the modernized mainframe

Enterprises have always regarded their mainframes as secure. But stiffening regulatory requirements, punitive fines for data breaches, and the growing threats of cyber-crime are forcing organizations to reassess their arrangements.

The mainframe generally lives outside enterprise security and relies instead on products such as RACF, ACF2, and Top Secret to implement access security control, so OpenText has introduced two game-changing solutions to extend enterprise-level security to the mainframe.

Centrally managed desktop terminal emulation with built-in security can ring-fence business-critical systems and data through masking and encryption, while the right solution enables automatic access for mainframe users.

Connecting the mainframe system directly to a multi-factor authentication (MFA) solution ensures authorized access only to business-critical host systems. Direct integration with advanced authentication creates an MFA protocol that meets regulatory, industry, and client standards.

Modernization and OpenText

The OpenText Modernization solution enables a transformational journey for the enterprise, on or off the mainframe. Our COBOL, mainframe application delivery, and host access solutions address the three pillars of modernization–application, process, and infrastructure–to achieve faster speed to market, competitive advantage, and operational efficiency.

OpenText mainframe solutions

OpenText mainframe solutions include specialisms for analysisdevelopmenttestingcontrol, and planning and management. Often treated separately, at least by host organizations, is mainframe access and security. Learn more about the wider marketplace, and our place in it, right here.


Unlock the value of host applications and data. Modernize access and integrate across new platforms. Accelerate deployment with DevOps practices and tools with these enterprise solutions.

Host Connectivity

Extend enterprise security to mainframe access, provide secure zero-footprint access to host applications (on-premises or in the cloud), integrate RPA with the mainframe, and automate terminal-based application testing. More here.



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