The main purpose of an information security management system (ISMS) is to reduce the frequency and impact of information security incidents. An ISMS is a systematic approach to managing information security risks, policies, procedures, and controls within an organization. An ISMS aims to ensure the confidentiality, integrity, and availability of information assets, as well as to comply with relevant laws and regulations. The other options are not the main purpose of an ISMS, but rather some of its possible benefits or components.
References:
* CISA Review Manual (Digital Version), Chapter 7, Section 7.11
* CISA Review Questions, Answers & Explanations Database, Question ID 205

The best method to reduce the risk associated with the transition to a new system using technologies that are not compatible with the old system is parallel changeover. Parallel changeover is a method of system conversion that involves running both the old and the new systems simultaneously for a period of time, until the new system is verified to be working correctly and completely. Parallel changeover can help reduce the risk of data loss, errors, or disruptions that may occur due to the incompatibility of the technologies, as well as provide a backup option in case of failure or malfunction of the new system. Parallel changeover can also help users compare and validate the results of both systems, and facilitate their training and adaptation to the new system.
Modular changeover is a method of system conversion that involves replacing one module or component of the old system with a corresponding module or component of the new system at a time, until the entire system is replaced. Modular changeover can help reduce the complexity and scope of the conversion, as well as minimize the impact on the users and operations. However, modular changeover may not be feasible or effective when the technologies of the old and new systems are not compatible, as it may create integration or interoperability issues among the modules.
Phased operation is a method of system conversion that involves implementing the new system in stages or increments, each with a subset of functions or features, until the entire system is operational. Phased operation can help reduce the risk and cost of implementing a large and complex system, as well as allow for testing and feedback at each stage. However, phased operation may not be suitable or efficient when the technologies of the old and new systems are not compatible, as it may require extensive modifications or adaptations to enable partial functionality.
Pilot operation is a method of system conversion that involves implementing the new system in a limited or controlled environment, such as a department or a location, before rolling it out to the entire organization.
Pilot operation can help test and evaluate the performance and usability of the new system, as well as identify and resolve any issues or problems before full-scale implementation. However, pilot operation may not be relevant or reliable when the technologies of the old and new systems are not compatible, as it may not reflect the actual conditions or challenges of operating both systems concurrently.
References:
* TRANSITION TO THE NEW SYSTEM - O'Reilly Media 1
* 10 Challenges To Think About When Upgrading From Legacy Systems - Forbes

IT governance should be driven by organizational strategies. It provides a formal structure for organizations to produce measurable results toward achieving their strategies and ensures that IT investments support business objectives12. While business unit initiatives, balanced scorecards, and policies and standards can play a role in IT governance, they are tools or methods that support the implementation of the organizational strategies.