[NTLUG:Discuss] OT: tapes and buffers

[Fred James]

All
This came up in a discussion of backups and tapes ...
    I was told that a tape has a minimum write speed, below which it 
"shoe shines" - that is when the buffer runs out the tape stops, 
reverses and repositions while waiting for the buffer to have something 
to write again.
    I was told that multi-threading (multi-buffering?) was the/an answer 
- a way to always have a buffer of data to write to the tape, and 
therefore stop "shinning shoes"
I have watched GUI displays of the tape writing process (or for burning 
a CD, for that matter) during which the "buffer" indicator would 
fluctuate from full to varying degrees of not so full, through out the 
process.
My question is how does the buffer work (or is that dependent on the 
particular software?) - does it fill and then not accept new data until 
it is empty again, or is it more like a pipe (input only limited by the 
capacity of the buffer, and output anytime there is anything in the buffer)?

Or am I asking the question wrong?
Thank you in advance for any help you may be able to offer
Regards
Fred James