12 bits for 2580 microinstructions
8 bits for 129 ctrl signals
so 1 ctrl word is 20 bits
so ctrl mem size = 20*2^12 bits
if your ctrl word is using 12 bits for microinstructions then number of control word is 2^12...and not 2580..
because WHATEVER IT IS YOU HAVE 2^12 MEMORY PLACES IN YOUR HARDWARE, WHETHER YOU USE IT OR NOT...
so 20bits*2^12 = 20*2^10 B= 20480 Bytes