Apparatus for using window signal generators to enable detection of header information such as an address mark, sector mark, or address information recorded on each sector of a disc recording medium only where such information could be present

An apparatus for detecting header information of a plurality of sectors recorded on a disc recording medium, the header information being recorded on each sector of the disc recording medium and being constituted by a sector mark indicating a head position of the corresponding sector, a plurality of address marks and address information data, said apparatus comprising:

• a) sector mark detecting means for detecting the sector mark of each sector and outputting a sector mark detection signal when detecting the sector mark;
• b) first window signal generating means for generating a first window signal which is in an open state when a predicted head position of the sector mark is reached and which changes to a closed state upon receipt of the sector mark detection signal;
• c) address information data detecting means for detecting the address information data from the header of each sector and outputting an address information detection signal when detecting the address information data;
• d) second window signal generating means for generating a second window signal which is in the open state when the predicted head position of the sector mark is reached and which changes to the closed state upon receipt of the address information detection signal;
• and
• e) third window signal generating means supplied with both the first window signal and the second window signal for generating a third window signal which is in the open state only when both the first window signal and the second window signal are simultaneously in the open state, and wherein the sector mark detecting means is supplied with the third window signal and is enabled to detect the sector mark only when the third window signal is in the open state.