Wanted: SIMH VMS quick test
RichA at LivingComputerMuseum.org
Tue Dec 16 13:13:02 CST 2014
From: Al Kossow
Sent: Tuesday, December 16, 2014 9:59 AM
> On 12/16/14 9:39 AM, Chuck Guzis wrote:
>> On 12/16/2014 06:29 AM, Al Kossow wrote:
>>> On 12/15/14 9:04 PM, Chuck Guzis wrote:
>>>> Okay, I've been working with my SCSI tape stuff and I'd like someone
>>>> to check a .TAP image on a VAX VMS SIMH setup.
>>> I looked at it with my tools. There are THREE extra bytes at the end of
>>> the first record, before the 50 00 00 00.
>>> Bob may pad to a short, but I don't think he pads to a long. The images
>>> I create don't pad a record at all, what you see is what you get.
>> http://simh.trailing-edge.com/docs/simh_magtape.pdf is the document
>> that I'm using for this. I clearly have some extra padding in the
>> records--that's a bug in my own padding routine.
>> The document does say that records will be padded to an even byte
>> boundary--is this incorrect?
> No, if that's the format you want to support. I personally think it is
> incorrect since that wasn't what was written on the tape.
It's a little more complex than that. Bob was using PDP-11 tape drives as
his model, and they *do* insert an extra null(?) byte at the end of odd-
length records. I think, but have not verified since my KS systems are
not running right now, that the RH11 on the KS's Unibus may do the same
thing, but for now that's just a guess.
Ken and Mark's tape format does not add a padding byte for KL simulation
by default, but distinguishes several different formats, including one
that is the same as Bob's.
My utilities which I wrote for TOPS-20 interactively inquire whether odd
length records should be padded or not, depending on which emulator I'm
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134
mailto:RichA at LivingComputerMuseum.org
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