The correct answer is A. Use a virtual machine to emulate an older OS , because virtualization is the most reliable method for running legacy applications that are incompatible with modern operating systems or hardware. When a new computer does not meet an application’s requirements—such as OS version, driver support, or system libraries—the issue is typically software compatibility , not system performance.

According to the Quentin Docter – CompTIA A+ Complete Study Guide , virtualization allows technicians to install an older operating system inside a virtual machine (VM) while still using modern hardware. This approach isolates the legacy application in a controlled environment that exactly matches its original requirements, without compromising the security or stability of the host OS.

The Travis Everett & Andrew Hutz – All-in-One Exam Guide explains that virtual machines are a preferred solution when organizations must maintain access to older business-critical software that cannot be updated. Running installers in Safe Mode or increasing swap space does not resolve OS-level incompatibility issues.

The Mike Meyers / Mark Soper Lab Manual further reinforces that compatibility toolkits can help with minor application issues, but they cannot fully emulate missing OS components or deprecated system calls. Virtualization provides complete compatibility by recreating the expected environment.

Therefore, using a virtual machine with an older OS is the most effective and exam-correct solution.