RSTS V7 magtape images on bitsavers

Paul Koning paulkoning at
Fri Feb 10 14:43:29 CST 2017

> On Feb 9, 2017, at 8:39 PM, Paul Koning <paulkoning at> wrote:
> Gents,
> I'm looking at a set of RSTS V7 magtape images (a release kit) which have an odd format that gives SIMH fits.
> In the container formats I'm used to, each tape block image is preceded and followed by the data length as a 4-byte value.  In SIMH that's rounded up to even, in E11 format it's not, but apart from that this is how things work.
> The V7 tape images don't match that format.  It looks like each block contains not just the data but also 2 more bytes, and the data length value represents that extra 2 bytes.  So the tape label is 16 bytes, not 14, and the data blocks are 514 bytes, not 512.
> Does this ring any bells?  Where do those extra bytes come from?  Can SIMH be told to deal with this or does it require a repair program to fix the format?

I wrote a simple program to strip off those two bytes everywhere, and the result was a set of V7 kit tapes that work nicely.  Trying to remember how to do a V7 installation with no docs was interesting...


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