Abstract: A demarcation circuit of the read channel of a disk drive identifies when the last byte of data prior to a servo block has been read, regardless of where the servo block is positioned, by generating an interrupt signal in response to the leading edge of a multi-byte marking signal when a time out signal is present. The time out signal is generated after a predetermined number of clock signals have been counted following the beginning of a servo block. The multi-byte marking signal is generated after a predetermined number of bytes have been counted. By insuring that the total number of bytes between servo blocks is a multiple of the predetermined number of bytes, the multi-byte signal will, at one point in time, identify the last byte of data.