SUMMARY: Enabling Sector Slip

From: Michael Maciolek (
Date: Fri Nov 08 1991 - 15:20:53 CST

Took a while to resolve this.

In my original request, I asked why I was seeing the message

        Warning: disk not set for slip-sectoring.

when I formatted a disk with what *should* have provided one
sector per track for sector slip. The appearance was that
'format' would not enable sector slip with fewer than two
spare sectors.


The problem: user error. <how embarassing!>

It appears that the real source of my problems was a non-default setting of the sector switches on the drive. Got the disk from a third-party vendor, and it had been formatted on an XY controller. I looked up the switch setting, which was supposed to yield a 600 byte sector (on a 41088-byte/track drive). However, it seems that format was only acknowledging 67 sectors per track, rather than the 68 that *should* have been there.

So I tried to format with 67 data sectors, expecting one spare for slip-sectoring, but as far as format was concerned, there weren't any spare sectors at all. Of course, it reported this at the end of the format with the warning message that I quoted.

When I changed my sector switches to the "standard" setting (which incidentally results in a sector size of 603 bytes), format *did* recognize the full 68 sectors/track. Gofigureit. After the change, I was able to format with 67 data sectors, and one sector/track really was reserved for slip-sectoring.

Thanks to all who responded, especially, who questioned my basic assumption about the correctness of the sector switches: +-------------------------------------------- |> Is there a FM that explains how to enable slip-sectoring on a drive, or |> one that explains how 'format' decides to format a drive for slip-sectoring? | |I thought it was just "at least one free sector". | |> I've got this disk that's got enough bytes per track to hold 68 sectors, | |Sure ?? | |> and I have proven that I can get it to use slip-sectoring by formatting |> the disk with 66 data sectors, leaving 2 sectors per track available for |> sector slip. | |Could be that it thinks that there is ONE free sector ... | |> This seems an awful waste, so I tried reformatting with 67 |> data sectors per track, and only one sector reserved for sector-slip. | |... meaning that one less -> 0 ! | Try using 68 and see if it succeeds ... +--------------------------------------------

Before changing sector switch settings, I did try using 68, and it failed:

Formatting...Hard sector count less than nsect. failed

Changed the sector switches to the 'approved' values, and it worked fine. I've reformatted to use just a single slip-sector per disk, and I am most happy with the results.

- Mike

------------------------------------------------------------------------------ Michael Maciolek (617) 981-3174 Network Engineer --- MIT Lincoln Laboratory Group 43 --- Weather Sensing ------------------------------------------------------------------------------ "She looked like she learned to dance from a series of still pictures." Elvis Costello - Spike, _Satellite_ ------------------------------------------------------------------------------

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