Grrr - !%#*^@# Kaypro!

[Allison]

>
>Subject: Re: Grrr - !%#*^@# Kaypro!
>   From: Fred Cisin <cisin at xenosoft.com>
>   Date: Wed, 03 Aug 2005 16:08:22 -0700 (PDT)
>     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>
>On Wed, 3 Aug 2005, Allison wrote:
>> Dave, your on track.  The CHRN vlaues do not have to corrospond
>> to actual head or cylinder.  They do not even have to be in order
>> on the media!   The only limits on them are R must be 1 or greater
>> (less than 255).
>
>Which creates some complications with handling 128 byte sectors (R==0).

???!  The value for R must be a valid sector number.  For floppies
that is never zero.

>
>> My favorite format was sectors 1- 9 (512 DD) on side one and
>> side two was 10-19 with H always set to 0.
>
>Easily handled by 765, but not by Int13h.

;-)  Plays havoc with many systems not expecting it.

>I have to be careful to differentiate which complications are
>due to the FDC chip, which to the FDC board/implementation,
>and which are BIOS linitations.

Yep, The bios for the most part is a not a limiting factor if you program
around it.  Its the board implmentations or the chips that replace 
board implmentations that really are poor.

>Nitpick: don't you mean 0 - 9 on first side?  Or did it actually have 9
>sectors on one side and 10 sectors on the other?

;) That was why it was pretty wild.  it was done for a joke in the lab
but no one could sort it out.

>I've seen disks with 10h and 20h in the H field.

Yep, CHRN are supposed to carry Cylinder, Head, Record(sector) and 
N=data length.  But the allowable values are usually 0 or 1 to 255.

One engineer at Bell Labs used a 765 to make a nice block replaceable
DC300 tape system.  He used R and H to form a 16 bit block number.
This was back in 1981 so it predates the PC based tape on floppy backup.

>And, of course, there are some formats, such as Superbrain,
>where the data (sector content) is inverted,
>but the headers (CHRN) are not.

that really bothered people for some reason.


Allison