On 5/22/23 13:49, Fred Cisin via cctalk wrote: > Unfortunately, the ability to handle single-density (FM) reading and > writing correctly IS one that some machines can; some can't. > > Although the 765 would have been capable of it, the 5150 FDC disabled > that capability. It is available on only SOME implementations.
Another can/can't is formatting and writing disks with 128 byte MFM sectoring. The National Semi DP8473 is one that can do both (FM and 128 byte MFM). Curiously, it's late P3 and P4 motherboard systems that have the best track record for this. However, Intel was not a leader in this department. The original 82077 FDC could handle FM just fine, but the later 82077AA-1 could not. When I brought this issue up to Intel applications engineering, the response was "So--who needs FM in this day and age?" Fortunately, the pin-compatible NSC PC8477 retained the FM capability. I recall when Micro Solutions recalled a run of their CompatiCard IV controllers with the 82077AA-1 controllers and replaced the chips wit the National ones. SMSC SuperIO chips have a pretty good record in this matter. --Chuck
