The .iso extension indicates that ACS 4.2 was delivered as a bootable operating system image, not a Windows application. It runs atop a stripped-down version of Red Hat Linux.
: A dedicated hardware appliance (like the Cisco 1113 platform) running a hardened, customized version of the Windows 2003/2008 operating system. "ACS 4.2 ISO" CISCO ACS 4.2.iso
Before you download a sketchy .iso from a random forum, consider these modern alternatives that behave like classic ACS: CISCO ACS 4.2.iso
I can provide specific configuration snippets to help you get your AAA services up and running. CISCO ACS 4.2.iso