ard at p850ug1.demon.co.uk (Tony Duell) wrote: Mostly true. Not completely raw, the drive incorporates most of the clock and data recovery circuitry. (Actually this is true on some MFM/RLL drives too!) In that way a little more like most SMD implementations. On PC-clones, most all the controllers were using the standard WD chipset and will have standard sector headers etc. One issue is that the largest ESDI drives used higher datarates (18MHz or 20MHz or higher) and not all controllers can handle such data rates. Outside of PC-clones, and into mini's/mainframes, some really funky bitstreams/sectoring were being used in drive arrays (where large numbers of >600MByte drives were sold to). In some cases the ESDI drives were used to emulate CKD drives, where the concept of a single fixed sector length doesn't exist at all (replaced by records and record lengths) and every time a dataset was laid down it effectively reformatted the track. In the early/mid-90's large numbers of ESDI drives were coming out of mainframe storage arrays and hitting the surplus market. Gees, that was 10 or 15 years ago :-). More modern CKD drive arrays use drives with conventional sectoring and do the funky stuff by packing up the emulated tracks into the regular-ish sectors. (I say "regular-ish" because it is still common to use 4096 or 8192 byte sectors, often plus a few extra bytes for overhead). This makes much more sense because a modern drive's track or cylinder will be larger than the whole disk the CKD array is emulating! Tim.