[net.general] R80, IDC, DMF32, etc...

ARPAVAX:shannon (06/20/82)

This is in answer to some recent questions and confusion
in net.periphs and net.unix-wizards about the RA80, IDC,
730, and DMF32.  If these questions have already been
answered elsewhere please excuse the redundancy, I've
been out of touch for a while.

The RA80 is one variation of DEC's winchester disk drive.
The drive itself is referred to as the R80.  When equipped
with Massbus interface logic it is referred to as the RM80.
When equipped with SDI interface logic (to connect to a
UDA50 for example) it is called the RA80.  When equipped with
neither of these (for example, when connected to the IDC
on the VAX-11/730) it is called the R80.  In all cases the
drive is identical, only the interface logic changes.

The IDC (also called RB730) is the "integrated disk controller"
on the VAX-11/730.  It interfaces the R80 drive and RL02 drives
to the 730's internal bus.  (Note that no RL11 controller is
used to interface the RL02 drives.)  All data transfers between
the 730 cpu and the IDC are done over the 730's internal bus, NOT
on the Unibus.  The IDC shares microcode with the cpu.  The IDC
can be used only on the 730.

The IDC bears no resemblance to the UDA50 Unibus disk controller
used with RA80 drives.  The UDA50 does indeed use a "network-like"
protocol between the cpu and the controller.  It is unlike any
previous DEC device but does show you what some future devices
will be like.

The DMF32 is a single board, eight line multiplexer with a sync
port and LP (or DR11C) interface.  The advantages over the Able
DMAX seem to be:

	1.  The LP and sync line - reduces board count in
	    smaller systems (like the 730).
	2.  The async lines can do XON/XOFF internally, for
	    what it's worth.
	3.  It's supported by DEC - if that matters.

The disadvantages should be obvious (cost, lines, etc.).  The
DMF32 is a Unibus DMA device and so should work on all VAXes
(or even 11's, but DEC won't sell them that way).

I have written drivers for the UDA50, IDC, and DMF32.  The
UDA50 driver is available from Berkeley now.  The IDC and
DMF32 drivers will be available in 4.2bsd.

				Bill Shannon
				ucbvax!ARPAVAX:shannon  (for now)
				Sun Microsystems Inc.
				(408) 748-9900