According to their functioning, which of the following is not a category of…

Computers are classified by their functioning — that is, by how they process and represent data — into three standard categories: Analog, Digital, and Hybrid.

• Analog computers process data represented as continuously varying physical quantities, such as voltage, temperature, or pressure.

• Digital computers process data represented in discrete binary form (0s and 1s).

• Hybrid computers combine both analog and digital processing techniques within a single system.

Checking each option against this classification: Analog, Digital, and Hybrid are all established functioning-based categories, matching the three types above. "Hydrobrid" does not correspond to any of them — it is not a term used in computer science classification at all.

• Analog — matches the continuous-signal category above.

• Digital — matches the discrete-binary category above.

• Hybrid — matches the combined analog-digital category above.

• Hydrobrid — does not match any of the three categories; it is not a recognized classification term.

Therefore, among the given options, the one that is not a category of computers (by functioning) is Hydrobrid.