When you see analog input DAQ devices from various manufacturers called 12-bit, 16-bit, or 24-bit, it generally just means they have an ADC (analog to digital converter) that returns that many bits. When an ADC chip returns 16 bits, it is probably better than a 12-bit converter, but not always. The simple fact that a converter returns 16-bits says little about the quality of those bits.
It is hard to simply state “the resolution” of a given device. What we like to do, is provide actual measured data that tells you the resolution of a device including typical inherent noise.
If you look at a device called “24-bit” just because it has a converter that returns 24-bits of data per sample, you will find that it typically provides 20 bits effective or 18 bits noise-free. some of the best performance around from a 24-bit ADC, and they do about 22 bits effective or 20 bits noise-free. You will see with these devices we might mention they have a 24-bit ADC (as that is what people look and search for), but we try not to call them “24-bit” and try to stick with the effective resolution.