Full CPU utilization regarding IPC is not just about the ALUs, it includes all units (ALU units, load/store, and other, e.g. if you have differentiated integer

Full CPU utilization regarding IPC is not just about the ALUs, it includes all units (ALU units, load/store, and other, e.g. if you have differentiated integer and floating point ALUs, etc.). E.g. with a 4 maximum IPC CPU (2 load/store, 2 ALU), on a synthetic benchmark doing only register-register ALU optimal work, you would get an IPC of 2. Also, depending on what algorithm you're doing, you'll never get the maximum IPC, even with optimal code, e.g. for a hash digest you don't need the store unit very much, so in the above CPU example you would reach an IPC of 3 with optimal code. So not always not having the maximum IPC means you're under-using the CPU for a given algorithm.