9 track tapes and block sizes
Chuck Guzis
cclist at sydex.com
Mon Oct 5 10:25:05 CDT 2020
On 10/4/20 10:51 PM, J. David Bryan via cctech wrote:
> On Sunday, October 4, 2020 at 16:00, Chuck Guzis via cctalk wrote:
>
>> A 16MB tape block is impossibly large in any case.
>
> The HP 3000 mag tape diagnostic attempts to write a single record from BOT
> to EOT, which unfortunately fails under simulation due to the 16 MB
> limitation. In hindsight, it would have been better to accommodate record
> lengths corresponding to the highest density and longest reel length, which
> I think would need 28 bits. Four bits for metadata identifier would still
> have been be good enough, and one of those should have been dedicated to
> "private data" that would appear invisible to programs running under
> simulation (and could be used to include information about the tape image
> with the tape image).
That's interesting. Looking at my own code for .TAP files, I see the
following:
#define TAP_FILEMARK 0x0 // 0 = filemark
#define TAP_EOM 0xffffffff // -1 = end of medium
#define TAP_ERASE_GAP 0xfffffffe // -2 = erase gap
#define TAP_ERROR_FLAG 0x80000000 // error flag bit
#define TAP_LENGTH_MASK 0x00ffffff // mask for length
So increasing the mask for block length wouldn't seem to be a problem,
assuming that SIMH could support it. There may be other high-order bit
meanings assigned, but I've not run into them.
--Chuck
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