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

[glen herrmannsfeldt]

Johnny Billquist <bqt at softjar.se> wrote:

(snip)

I should probably remember, but I don't. Are DECtapes factory formatted
and can't be low-level formatted by the user?

Or maybe only the timing track?

Many tapes now have a servo track that is factory written 
(LTO, for one) and so can't be bulk erased and reused.

> Right. In which case, if we want to read blocks 0,1,2, we actually need 
> to read physical block 0,2,4, which means you can't set up the 
> controller to read multiple blocks, but instead have to issue an 
> individual read for each block. It then also becomes a seek between each 
> read, and then you need to make sure that there isn't a stop-and-go 
> effect between the read of one block, and the read of the next block.
> Not to mention that you still need to know in which direction to read 
> the blocks, so that you don't get that wrong. :-)

If it can be reformatted, then you can write the new block numbers
into the block headers. Otherwise, yes, you need to map to the 
physical block numbers.

-- glen