[Info-vax] TK50 - this is annoying...

[Johnny Billquist]

On 2012-10-19 00:46, glen herrmannsfeldt wrote:
> Johnny Billquist <bqt at softjar.se> wrote:
>
> (snip)
>> But since blocks on a DECtape are numbered when formatting, and the
>> formatting just runs through the tape from start to end, the blocks on
>> the tape will be numbered 0,1,2,3,4,5,6,7,8,9. Which also means that the
>> above suggested idea for writing would mean you need to get a map of
>> which logical blocks maps to which physical blocks. Not forgetting that
>> you need to know when to switch over from forward to reverse operations.
>
> Are they factory formatted, with the block headers never rewritten?

You can reformat the tape yourself, if you want to. However, if you 
don't place the blocks in the correct order, you are going to mess up so 
much software that you'll never recover, since the DECtape uses the 
block numbers to figure out in which direction to spin to get to the 
requested block.

> As in the case of 8 inch floppies, it can be done through a remap.

Yes.

>> And in general, this would just about half the speed of your DECtape.
>> Simply because reading all the data on the DECtape now requires you to
>> run over the tape two times, while without this scheme you'll read all
>> the tape by running over it one time.
>
> But, if you include rewind, the time might be the same.

But rewind can be done afterwards, when I don't care. I got the data in 
half the time. The rewind still needs to happen, but while that is going 
on, I can do other work.

	Johnny