The disadvantages of older systems, is that they are considered expensive to maintain, cannot be updated without significant effort, and lack the flexibility to an interface (connect to) and exchange

The disadvantages of older systems, is that they are considered expensive to maintain, cannot be updated without significant effort, and lack the flexibility to an interface (connect to) and exchange data with newer ITs or to take advantage of Internet-enabled business processes. Because of their challenges, when companies need to update mission-critical legacy systems, they usually turn to enterprise information system software.

This is NOT to say that mainframes are dead, they are far from it. 

What is a mainframe? It's a style of computing (Links to an external site.)Links to an external site. (IBM Knowledge Center)

Enterprise information systems, or simply enterprise systems (or enterprise software), integrate core business processes and functions that you read about in Chapter 9. Integration is achieved by linking databases and data warehouses so that data can be shared with:

• Internal functions: Functions that take place within the company, which are referred to collectively as the internal supply chain.
• External partners: Business or supply chain partners, such as customers or suppliers. These constitute the external supply chain.

(chapter 10, quick look, para. 1)

The acronym ERP stands for enterprise resource planning. It refers to the systems and software packages used by organizations to manage day-to-day business activities, such as accounting, procurement, project management, and manufacturing. ERP systems tie together and define a plethora of business processes and enable the flow of data between them. By collecting an organization’s shared transactional data from multiple sources, ERP systems eliminate data duplication and provide data integrity with a “single source of truth.”

Today, ERP systems are critical for managing thousands of businesses of all sizes and in all industries. To these companies, ERP is as indispensable as the electricity that keeps the lights on.

                                                                                                                                       (Oracle, 2018, para 1)

What is ERP?ERP stands for Enterprise Resource PlanningWhat is the simplest ERP definition? Think about all the core processes needed to run a company: finance, HR, manufacturing, supply chain, services, procurement, and others. At its most basic level, ERP integrates these processes into a single system. But new ERP systems are anything but basic. They provide intelligence, visibility, analytics, and efficiency across every aspect of a business. Using the latest technologies, ERP systems facilitate the flow of real-time information across departments and ecosystems, so businesses can make data-driven decisions and manage performance – live