APT (APF Imagination Machine)
APT is a format used by an emulator program to store the data contained in an APF Imagination Machine data cassette. It contains the sequence of bits/bytes encoded in the cassette, without attempting to capture audio data or the raw specifics of the frequency and amplitude of data pulses.
A file will be of variable length, and consists first of the "leader" portion before the actual data starts: a number of 00 bytes (nulls), representing a sequence of 0-value bits, ending in a byte value of 01 which begins a sequence of 1-value bits represented by a series of FF (hex) bytes, terminating in an FE byte (where the last bit is zero, ending the leader).
The data follows, which, if it is a normal CSAVE program file, will consist of 512 bytes to be displayed on screen memory followed by the tokenized BASIC code.