CompuServe Messages

The chips are not pin compatible, plus they run at a different clock rate. Also, you are comparing apples and oranges. MFM is 5 mbit, RLL is 7.5 mbit, and ARLL is 10mbit. MFM,RLL, and ARLL only refer to the method of encoding the data bits on the hard drive. ST506/412 on the other hand, is a hardware standard for controlling a hard disk. This standard specifies what are the data lines, the control lines, and the needed voltage levels. Since a hard disk is a very dumb device, you need another processor to handle the data encoding/decoding, head positioning, ect. Next, you need a front end, some standard method of sending/receiving data. This would be your IBM bus, SCSI, or ESDI standards. So you now have the Adaptec AC2000, which is a ST506/412 -> IBM bus controller. The Adaptec AC4000, which is a ST506/412 -> SCSI controller. The Adaptec ???? which is a ST506/412 -> ESDI controller. And the Adaptec ??? which is a ESDI -> SCSI interface. SCSI and ESDI integrated drives combine several of the above processers into 1 processer. Thus cutting costs and form factors. I suspect that we will see ARLL mostly impelmented in the integrated drive format. [Mark]