DILOG DQ-614

From: Jerome Fine <jhfine_at_idirect.com>
Date: Fri Aug 3 18:40:41 2001

>Sergio Pedraja Cabo wrote:

> > You can have up to 4 drives per controller, and up to 2
> > controllers per
> > system.
> Ok. This is good.

Jerome Fine replies:

I understand that the hardware limits the number of drives per controller
to 4 drives. But, I can't see why there is a limit to the number of
controllers. In RT-11, I am allowed to name a different device driver
any name I wish. While I personally allow two controllers on my systems,
having many more names would not be a problem so long as the
CSR/VECTOR pair are unique and do not conflict with any other
hardware values. Of course, these days I would not use an RL02
for anything but a transfer media. But ten years ago when an RQDXn
was much more expensive, if I would have been given the RL02
controllers and drives, I might have used up to 16 RL02 drives on a
single system. I am not sure where the cabinets would have gone
or how much power it would have drawn or if it would have been
beneficial, but it could have been done.

Actually, just for a test, I presume that it might be a challenge to ask
one of the emulator products to allow up to eight controllers and just
for the fun configure a system with eight device drivers in RT-11?
DL:, FA:, FB:, FC:, FD:, FE:, FF:, FG: and set up 32 container files.

> > BTW, RD5x drives are usually seen as DU devices, not as DL ones.
> Mmmm... This board treats one Mfm Hard Disk attached to it
> like up to four DL drives, from DL0 to DL3. The drive must
> be partitioned with one partition by drive emulated. That is
> what can be deducted reading the (poor) info that could be
> located in the Internet.

Any controller can emulate any hardware. While an RQDX3 accepts
only RD5x drives and makes them look like an MSCP device, in fact
that is also an emulation - just as an VT100 emulates a VT100 terminal.
Just because something is emulating itself or what it actually is is no less
of an emulation.

> We speak about one RD52. I suppose it could be divided in three
> DLx emulated drives.

When I used an RD52 on a DM01 from Emulex, I was usually able
to state the actual number of cylinders, heads and sectors per track
to produce 40 MBytes, i.e. a Quantum 540 hard disk drive could
provide about 80,000 blocks of 512 bytes even though DEC
allowed the RQDXn controllers to see 60,000 blocks. On that
basis, if you actually have an RD52 that is being formatted by the
controller, see if you are allowed to use four emulated RL02 drives.

Also, just because DEC used 5 1/4" full height drives (RD5x) with
RQDXn controllers to emulate MSCP hardware does not mean
that is the only option. In fact, the Dilog use of an MFM hard drive
to emulate RL02 drives (non-removeable of course) was just one
of over a dozen different types of using some hardware to look like
other hardware.

Another example is a Sigma RQD11-EC quad Qbus ESDI controller
which used ESDI hard drives to look like large MSCP hard drives.
Dilog did this as well. There are also a number of Qbus host adapters
which use SCSI hard drives and most (probably all) emulate MSCP
"emulation".

Sincerely yours,

Jerome Fine
Received on Fri Aug 03 2001 - 18:40:41 BST