Disk on my NIC-80

From: Dwight Elvey <elvey_at_hal.com>
Date: Mon Apr 10 15:38:19 2000

Hi All
 Well, I've started to reverse engineering the disk
drive on this machine. Looking at things, I think
it is a hard sectored controller ( 8 inch drive ).
There is a circuit that looks like it is for
separating the index hole from the sector holes.
As I recall, the index hole is spaced half way between
two sector holes. It uses a 74121 one shot to detect
this signal. The resistor and capacitor give the following
timing: 0.7 ( 0.22e-6 * 22e3 ) = 3.4 ms. I would think
that this signal would be about 3/4 of a sector to
catch the index mark in the middle. As I recall,
8 inch disk rotate at 360 rpm ( help me here, is this right? ).
That would be 166.7 ms per rev. Now, X * Y = 166.7
with X = sector time and Y = number of sectors. If I assume
that 3/4 * X = 3.4 then X = 4.5. Y would then be 36.9.
 My question is, does this sound like a reasonable hard
sectored 8 inch disk? Do they come in 32 sectors
or is there a flaw in my calculations someplace?
The number of sectors should be between 25 and 50 someplace
according to my calculations. 32 would make the most sense.
 There is also a counter that only counts to 8 before cycling.
Could they be logically dividing the disk into 4 blocks?
The data word size is 20 bits and not 8 bits.
 If so, anyone have any of these hard sectored disk?
What are standard sizes for sectoring of 8 inch drives?
Dwight
Received on Mon Apr 10 2000 - 15:38:19 BST