In the apparatus disclosed herein, data recorded on a floppy disk in double density MFM mode is read back using a digital, adaptive time base system which permits accurate recovery of data despite bit shifting due to a high bit density on the magnetic recording surface. The adaptive time base provides...http://www.google.com.tw/patents/US4281356?utm_source=gb-gplus-share專利 US4281356 - Magnetic disk memory
