I know standard air data computer can produce true air speed with total air pressure, static air pressure, and total air temperature. But for a low speed aircraft <100 knots, do I need to install a total air temperature sensor or other temperature sensor to get the true air speed computed? Or air temperature is not needed for low speed aircrafts and the air data computer can produce the true airspeed based on the calibrated air speed?
A good chunk of aircraft operating in the <100Kt range generally don't have Air Data Computers although glass cockpits are becoming more and more common in general aviation aircraft. For good old steam gauges a sliding temperature compensation scale is built right into the Air Speed Indicator, for more info on that see this question or this video. OAT is determined generally by a thermometer installed on the windscreen or in the side window.
If your aircraft is equipped with with a capable glass cockpit you may be able to get TAS from the system
The Airspeed Indicator displays airspeed on a rolling number gauge using a moving tape. The true airspeed (TAS) is displayed in knots below the Airspeed Indicator.
The G1000 has an OAT gauge as part of the install.
The Outside Air Temperature (OAT) and the deviation from International Standard Atmosphere (ISA) temperature are displayed in degrees Celsius (°C) by default in the lower left of the PFD under normal display conditions, or below the groundspeed in reversionary mode.