On 2013-03-28 03:08, Bob Supnik wrote:
I believe the PDP-10 DECtape images that are floating around the web may
not be accurate transcriptions.
All the images are 289KB long. An 18b (36b) DECtape consists of 18b
words in a 32b container (a 36b word in a 72b container). Thus, each
256W x 18b (128W x 36b) DECtape block requires 1KB of dusj storage.
Therefore, the unage length, in KB, should equal the number of blocks,
which is 578. And in fact, all extent 18b PDP DECtape images are 578KB
long.
A 16b DECtape consists of 16b words in a 16b container. Thus, each 256W
x 16b DECtape block requires 1/2 KB of storage. Therefore, the image
length, in KB, should equal half the number of blocks, or 578 / 2 = 289.
And that's what we have.
This is confirmed by the fact that if you let the simulator "autosize"
the 289KB images, it comes up with PDP-11 format.
I verified, by patching the simulator, that there is data in both halves
of each 32b word in the image. This too points to a PDP-11 image.
Even if the PDP-10 DECtape were packed with no padding, it should be
18/16 = 9/8 the size of a PDP-11 image, or 325+KB. So I think the images
were transcribed on a TC11 and are missing 2b in every 18b.
This is not to say that the TD8E simulator is correct. I cannot get it
to zero (initialize) a fresh 18b DECtape through PIP10, so something is
broken. However, the TD8E is so arcane that it will take a considerable
period of time to figure out what the software is trying to do and why
the simulator is responding incorrectly.
I don't know if I'd call the TD8E arcane. Like I said before, it is the
most stupid controller ever invented.
I had to write code last year to extract 18b images from a PDP-15 using
the TD8E. Reading through the documentation, and reading through the
TD8E driver as well as PIP10 was enough for me to understand how it
worked, so you should be able to do the same.
Basically, the TD8E gives you almost nothing at all. You need to do just
about all the fiddling yourself.
It is horribly stupid and primitive.
Johnny
_______________________________________________
Simh mailing list
[email protected]
http://mailman.trailing-edge.com/mailman/listinfo/simh
