On Wed, 12 Jan 2005 09:05:22 -0600, Wolfe, Julian wrote:
>*OK<*setting up my magtape unit here on my 11/23, I'm trying to
>*igure out what some terminology means. *The DQ130 card emulates a
>*"Streaming" device according to this page:
>*However, I found out by the manual to my Overland OD3201 magtape
>*unit that it is a "Pertec Formatted" device.
>*What does this all mean?

Mixed up terminology will do that to one!

There are basically Two kinds of tape drives

Start-Stop and Streaming

Start Stop drives are designed to "start, write a block, stop" without
having to reposition the tape. This is achieved by using fine control
of the tape using a capstan and either vacuum columns, or swing arms.
(Swing arms are SLOW, whereas vacuum colums are faster).

Streaming drives are designed to go forward with as few stops as possible.
So, the idea is to buffer as much data as you can and then write without
stopping. There are streaming drives that make this easier by having
an on-board cache (eliminating need for a lot of controller buffering) or
simple ones that rely on the system keeping up! Streaming drives will
do start-stop, but they have to do a reposition every time to start from
the right place. This makes them VERY slow.

Now, most newer drives are streamers ... but the older drives are
mostly start-stop. The TM-11 is one of DEC's original start-stop
drives ... So, the DQ-130 emulates a TM-11 on a streaming drive. It
does a lot of buffering to do this.

There are a number of different interfaces between the tape controller/
coupler and the tape drive ... the most common of these is the Pertec
format interface. There is also an IBM interface and an STK interface
and a SCSI interface and the CIPHER interface ..... and so on.

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