Looking for a ST419

Did these MFM interfaces and associated controllers ever expect to write individual sectors on a track? or was the entire track always written at once? I realize that the operating system had individual sector write-ability but was that accomplished by read-modify-write of that individual sector in a controller buffer and then the entire track rewritten? or did the controller sync to the beginning of the specific sector and write it in place? I'm still dreaming about a way to emulate these drives with modern hardware and I know that has been hashed over a lot over the years... but I have no interest directly mapping an old drive to a new one. I'd be happy with emulating the old drive in a file (image) on a new drive or say, compact flash or other non-rotating media. -- Chris Elmquist mailto:chrise at pobox.com