Skew vs. interleave

[Paul Koning]

> On Jul 30, 2021, at 5:35 PM, Mike Stein via cctalk <cctalk at classiccmp.org> wrote:
> 
> There's a small discussion on S100computers about the terms 'skew' and
> 'interleave'.
> 
> In CP/M documentation 'skew' refers to what's usually called interleave
> these days, i.e. offsetting sectors on a track to compensate for the fact
> that by the time the computer has processed a given sector the next one has
> already passed by, so that the computer has to wait an entire revolution
> for it to pass by the head again; in other documentation as in Chuck's
> 22disk for example this is also called 'interleave'.
> 
> However, in later documentation the meaning of 'skew' seems to have changed
> to refer to the offset of sectors between adjacent tracks to compensate for
> the time required to step the head.

I've only ever seen the term "skew" with that second meaning.  The first thing you mentioned in my experience is always called "interleave".  For example, the DEC RX50 has 2:1 interleave and 3 sector skew.

Interleave is normally written as the physical sector number difference of two logically adjacent sectors (so 2:1 means there is one other sector between logical sector 0 and logical sector 1).  In one place (David Gesswein's MFM emulator) I've seen it used the other way around, n:1 meaning that logical sector n is physically immediately after logical sector 0.

	paul