This page is currently a stub, as there is very little information on this aspect of WebTV. E-mail us if you have any more information on this subject.
FIDO is an ASIC used exclusively in the Classic WebTV boxes (Sony INT-W100 and Philips Magnavox MAT960) released in 1996. The ASIC acts as both a graphics processor that handles output to NTSC and PAL standard televisions, and also handles other core system functions, such as IR and managing LEDs.
So far, not much else is known about FIDO. The FIDO chip is usually located at the center of the box's motherboard, with the WebTV logo and the text "FIDO" printed on it.