[Simh] VAX Tape Emulation?

[Clem Cole]

Zane,

I'm not sure I follow your question.  Tape sizes are defined by the reel,
not the recording hardware.  Since the device is a vector (starting at
block 0) are conceptually unlimited (fixed by the number of bytes/blocks
available in the length of tape).   9-track mag tapes in 12" reels were
traditionally 2400 ft long.   3M managed to make a thinner tape and got the
tapes to 3600 ft.   The 6" reels were 600 ft and the 10" reels were 1200 ft
BTW.    But the recording techniques (aka the tape densities) defined how
many bytes [NRZ - aka 800 bpi, PE - aka 1600 bpi, GRZ - aka 6250].   The
other issue is/was how big a 'block' you can write.   Anything more than
64k bytes could be problematic as the IEEE tape standards did not define
reliable ways to do that and on a VAX or PDP-11 that was traditionally the
DMA size limit anyway.

Anyway, with traditionally blocking, a 2400" tape @ 6250 you could get
about 120M of storage (~180M on 3600 " tapes) --  put another way, we used
assume that an RP06 could be backed up on 2.5 tapes.

Disks on the other hand are not a vector, but rather # of heads, #of
cylinders and the # of sectors in each cylinder.  Thus they have a more
fixed size.

Clem
ᐧ

On Wed, Jan 24, 2018 at 5:02 PM, Zane Healy <healyzh at avanthar.com> wrote:

> What type/size of tapes does the VAX emulation support?  I was looking
> through the doc’s and it wasn’t obvious to me.  Is there a size limit?
>
> Thanks,
> Zane
>
>
>
> _______________________________________________
> Simh mailing list
> Simh at trailing-edge.com
> http://mailman.trailing-edge.com/mailman/listinfo/simh


ᐧ
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.trailing-edge.com/pipermail/simh/attachments/20180124/932d54e9/attachment.html>