Re: Yeah, no
Many things in your post are incorrect.
1. The Apple II did not use variable-speed drives. You are probably thinking of the much later Macintosh.
2. The first 5.25" floppy disk controllers were no slower than later later ones* and hard sectoring was not because controllers were too slow to do soft sectoring. All controllers were capable of reading and writing a full track in a single revolution: this is exactly how formatting a diskette works. Most programs for doing a sector-by-sector copy of a disk read tracks – whether the sector numbering was interleaved or not – in a single revolution as well.
3. The interleaving was due to the _operating systems_ being slow because they weren't willing to dedicate buffer space for a full track and were otherwise too slow to finish their own processing of a sector _after_ it had been read into memory but before the next sector came up. (The FDC was perfectly capable of immediately reading the next sector if the OS/application had been ready to do so.)
4. The NEC D765AC FDC used in the original IBM PC was not significantly more capable than early chips such as the Western Digital FD1771. The improvements in FDCs between the mid-'70s and early '80s were mainly in integration and requiring less support circuitry.
*Modulo the FM vs. MFM thing, and support for even higher densities, which I won't get into here. Note that the very early Western Digital FD1781 even supported double density because it used external modulation and demodulation circuitry; later chips that had higher levels of integration and brought this circuitry into the chip were often less capable than this because they didn't use modulation circuitry capable of supporting double-density operation.
Biting the hand that feeds IT
