IPS tape drive

[utzoo!decvax!ucbvax!unix-wizards]

>From mo at LBL-UNIX Tue Nov 10 06:09:51 1981
I now have an IPS/Telex Triple-density Unibus tape subsystem running on
a VAX 11/780.  It resembles an RH11-TM03 pair (TU16 on the Unibus) with
some differences.  I don't have the toggle-in driver or stand-alone
driver yet, and some of the edges are still rough, but it runs like a
champ.  When I get it polished up and the other two drivers done, I
will make it available to other sites.  The IPS controller has a
32Kbyte buffer so you have LOTS of time to do things.  In fact, there
is a "Data Chaining" mode whereby the transport doesn't stop moving
when DMA runs down.  You can take the interrupt, start the DMA again,
and keep going, reading or writing VERY long records.  The IPS comes
with a VMS driver and diagnostic program.  One of the diagnostics
consists of writing 5,000,000 byte records and reading them back!!!!!

I don't have the data-chaining stuff in yet, but it will be enventually
(don't know about reading/writing records larger than physical memory,
however; VMS stuff uses page map/unmap cruft).  That would allow full
DD-style dumps (c.f. George Goble's previous note) to go very fast.

I will talk about this at January Usenix meeting in Santa Monica.

	-Mike