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

[Johnny Billquist]

On 2012-10-19 15:44, Bob Koehler wrote:
> In article <k5p9uo$d52$1 at Iltempo.Update.UU.SE>, Johnny Billquist <bqt at softjar.se> writes:
>>
>> If people actually thought about it... I mean, a PDP-11 could keep a
>> disk fed with data without missing blocks, and disk blocks pass by much
>> faster than tapes...
>
>     ?
>
>     We always had to resort to 9-track to keep up with data flows on a
>     PDP-11 on a hard real-time system.  Are you telling me there were
>     disks that fast?

Not really sure what you are talking about now...
Are you telling me that reading/writing tapes were faster than disks for 
you?

The fastest tapes on a PDP-11 is the TU77, which writes at 125 ips. At 
1600 bpi, that means it writes 200,000 bits per second per track, so 
approx 200 KB/s. And this is disregarding the block gaps, where it will 
pause.

Are you saying that no disks you had could exceed that?

A normal RP05 or RP06 will transfer 806 KB/s, just as comparison.

And both the TU77 and the RP drives hang off massbus, so the speed 
outside of the drive have the same restrictions, so no way the disk 
could ever be slower than the tape.

Maybe if you were doing lots of seeks on the disk...? But that is not 
what I was talking about above...

	Johnny