GCR Encoding

["Bryan Parkoff" <bryan.nospam.parkoff@nospam.com>]

    Can Disk II Family read three or four (zero) bits that it will always
show invalid?  Is it the truth that Disk II's hardware is designed to read
only one or two (zero) bits?  Can you explain why?  Why do each byte require
between $80 and $FF?  I do understand that between $00 and $7F can't be used
because it will show more than two (zero) bits.
    How did Steve Worniak decide to design logic chip that can only handle
two (zero) bits?  I do know that he decides to use software by reading each
bit.  If software is chosen to use without from hardware's help, two (zero)
bits can be accurate because the rotation speed may vary.  If hardware is
chosen to use its own hardware, three or more (zero) bits can be accurate
because the rotation speed is always fixed.
    I do see that most copy-protected disks contain more than three (zero)
bits.  If it is true, it is called weak bit that GCR encoding could detect
three (zero) bits before it can skip to continue reading next valid bits.
    I am so curious why Apple II decide NOT to use standard MFM encoding
that it does exist before 1970s, but all PC like 8080 and/or 8085 use MFM
encoding (probably FM encoding) before 1970s.  Please explain every detail
if you have great knowledge.

-- 
Bryan Parkoff