Drives on PDP-11

From: Allison J Parent <allisonp_at_world.std.com>
Date: Sat Mar 25 21:19:39 2000

<I have a full backup of the drive via COPY. I would like to graft a
<different hard disk onto this machine.

If the second slot is clear you can run two hard disks. that means pulling
the floppy to do it. You don't however wire it like a PC.

<How do connect the second drive? There are connections for a second
<drive but both are on the machine and not with the 34 pin connector
<daisy-chained to the first drive as is normal. Do I terminate each drive
<in this "Y" configuration? What drive number should it be? Drive 4 I
<suspect as the first and only hard disk is set at 3 and is terminated.

No. You use two 34s and two 22s you will see drive o and drive 1 on the
plate behind the HD/floppies. RT11 has a logical drive limit of 32mb
so a good drive is the RD52 (quantum D540) as it's both 31mb and of all
the MFM drives I've used it's rugged and reliable. The largest drivew
the RQDX3 can handle is 16hx17sectors by some 2048 cylinders (~500mb)
but the largest ever used by DEC was the RD54 (159mb, Maxtor 2190).

<How would I configure drive geometry to match the drive I am installing?

If the drive is formatted DEC compatable (PC cant!) the controller is smart
enough to figure it out. If the drive is formattet non-dec you need the
PDP-11 formatter to do it or a microvax2000 (has a formatter in rom).

<The object of installing a second hard disk is to create a bootable clone
<of the first one. A bump in disk space is allways cool but I want a
<bootable clone as a backup at least.

You can backup to floppies. RX50 is ~400kb a disk.

<Does the ST506-type controller have enough Shugart SA400 about it that it

The controller is not a the PC style of st506(which is a drive interface
standard). The RQDX controller is extremely smart and has it's own PDP-11
in the form of the T-11 chip. The controller take the MSCP protocal and
does a lot of work to translate that high level protocal to actual drive
activity. I does so basic caching and queueing as well and uses DMA to
get and put command and data. Nothing like that in your average PC that
used similar MFM drives.

<is running the floppies as drive id's 1 and 2? It would explain a lot.

Sa400, never much too small. If it is RQDX3 (dual width board) then you
can use or or two of the TEAC FD55GFV to get both RX50 (400kb) and RX33
1.2mb formats.

<How difficult is it to substitute a standard double-sided floppy mech for
<the wierd but nifty-looking floppy drives that are in it now? For those
<of you still wondering, it has an RX50-AA double-drive unit that cannot be
<formatted by the computer but can be read.

Correct, formatting is not permitted by the controller due to software and
the DEC RX50 drives were junk. You can format disks on PCs... PUTR can
but you much have dual mode 1.2mb drive like the teac mentiond.

<Will I be able to format media on the machine if I DO replace the drives?

No. Yo need the diagnostic to drive the controller.

<Can I substitute a standared 40trk X DS X DD mechanism or an 1.2mb 5.25"

NO. Both the RX50 and the FD55gfv are 96tpi.

<mech to accomplish this? The connections look standard though I have not
<opened the base enclosure for the floppy mechanism for a look at it's
<cabling yet.

The cabling and interface will run standard 5.25 96tpi drives.

Bet you got more than you wanted. But all of the burried majik is why
in 1987 11/23 (or 11/73) could support a raft of users with a cpu that
some considered a wimp compared to the mighty 386/16(which still cant)

Allison
 
Received on Sat Mar 25 2000 - 21:19:39 GMT