In a typical wca4z deployment, on which platform do the ADDI server components run?

Think of it like working hands-on with IBM mainframe systems — the answer here is 'ADDI components must reside on the z/OS LPAR alongside COBOL programs'. ADDI server components run on standard x86 Linux or Windows servers that have TCP/IP network connectivity to z/OS, not on the mainframe hardware itself. On real mainframe exams, this concept comes up repeatedly so make sure you have it locked in.