22 May
2023
22 May
'23
9:25 p.m.
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