Pertec T8640A Tape Transport

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I have a Pertec T8640A Tape Transport that is now working nicely on a QBUS PDP-11 system.

While I still have a lot to learn about the operation of magtape systems (and their advantages and limitations), I am now able to successfully “INItialize”, write to and read from magtapes in this Tape Transport.

This Tape Transport is currently mounted in a full-height DEC rack. The rack also has a General Robotics QBUS chassis in it, as well as an MPI CMD Model 9448 hard drive. I’ve not been able to find any information about an MPI 9448, though there is a brochure on the web about a CDC 9448, which appears to be the same drive. The CMD drive actually has a 16MB fixed hard drive and a removable 16MB cartridge drive in the one enclosure. The removable cartridge is a Nashua 4420, and is not compatible with DEC removable-media drives. I have not yet got the SMD drive working.

The QBUS chassis is fairly well equipped. It includes:

  • M8192 processor
  • [RAM board]
  • 2 x Webster terminal multiplexers
  • 2 x DEC DLV11-J 4-port SLU board
  • An Emulex SC02 board to support the SMD drive
  • An Emulex TC01 (2-board set) to support the Pertec T8640A Tape Transort

The Tape Transport has 3 x 36-pin edge connectors on it. An Emulex cable kit connects 2 x 40-way ribbon cables to these edge connectors. At the other end of each of the Emulex cables is a 40-pin header connector (so two 40-pin header connectors in total). These two header connectors have handwritten notes on them that say respectively “long board” and “small board”, suggesting that they perhaps connected to a 2-board interface of some kind?

Photo Gallery

Here are some photos of the Tape Transport and the rack in which it was found.

Here are some photos of the Pertec Formatter (I am not sure if this is part of this system).


I have the following hard-copy manuals:

  • Models T8640A and T8660A Synchronous Write Synchronous Read Tape Transports, Operating and Service Manual No. 103381
  • NRZI Formatter Model F8X9, Operating and Service Manual No. 101600

Tape Transport

The Tape Transport has 3 x 36-pin edge connectors numbered J101, J102 and J103.

The diagram on the right shows the pinouts for these connectors. It is page 2-6 from Manual 103881.

Pertec Formatter

Unfortunately this Formatter does not have any manufacturer name or model number on it, except for the “Pertec” badge on the front panel. It does however look very similar to the formatter shown in the F8X9 Manual listed above. So for the time being I assume that is what it is.

The F8X9 Formatter has 2 x 100-pin edge connectors numbered J101 and J102. J101 connects the Formatter to the Controller. J102 connects the Formatter to the Tape Transport.

The diagram on the right shows the pinouts for these connectors. It is page 2-4 from Manual 101600.

This formatter does not appear to be part of this system. I do have two other Pertec T8640A tape transports (without the 3rd borad, which is for 1600 BPI), and I assume this formatter was intended to be used with one of them.

“Pertec Interface”

I am aware that tape drives on PDP-11 systems usually have two 50-pin header connectors (referred to as the “P1” and “P2” connectors).

Chuck Guzis has a webpage that describes the pinouts for the Pertec Interface.

A typical interface board for tape drives is the Dilog DQ132 board. I don’t have a manual for the DQ132, but I do have a manual for a DQ130.

Loading RT-11 on to magtape

Copying RT-11 on to the magtape was easy.

Here are the commands:

  • INI MT0:

However the COPY/BOOT command (COPY/BOOT MT0:RT11SJ.SYS MT0:) does not work. Need to work out how to make a magtape bootable.

Note: The Pertec drive is unfortunately very unreliable. Typically if I try to copy several files to it, it will fault after copying 1-2 files. The tension arms will go limp, and the system will hang. At this stage I don’t know where the fault lies. I have tried about 6 different tapes and I have the same problem each time.

Building the system out

In September 2017 I took another look at this system. I’ve made the following changes over the past few months:

  • The huge white/orange SMD drive shown in the photos above has been removed. It was non-responsive. The Emulex controller for it is still in the QBUS chassis, but the drive itself is long gone.
  • A terminal multiplexer board and a 4-port SLU board have been removed, to make way for the Webster SMD interface.
  • The second terminal multiplexer board was removed, to make way for an RXV21 (M8029) board.
  • The Pertec tape transport has been moved to the top of the rack.
  • A TS05 drive now sits below the QBUS chassis. It is not yet cabled in to the QBUS chassis.
  • An RX02 drive sits below the TS05. This is working fine and can be used to boot the system.
  • A Fujitsu SMD drive sits in the bottom of the rack. Off hand, I can’t recall which model it is, but a label on the top of the drive says “M233x”. It is cabled up to a Webster SMD controller card and appears as drive DU0. This drive now has RT-11 V5.03 on it. It can’t be used to boot the system, because the console boot menu (a text-based system that starts with a “$” prompt) doesn’t support booting from a DU device.

When the system is powered up, a “$” prompt appears on the console. I don’t know where there is coming from, but I suspect it is a monitor running on the Emulex board that used to be connected to the (now removed) large SMD drive. I’ve not been able to locate any built-in help menu for it. However, 2 or 3 letter commands starting with “D” seem to be able to boot various devices. From trial and error, it appears the ROM supports only the following: DB, DD, DK, DL, DM, DX and DY. I’ve successfully used this ROM to boot DD0 and DY0. Note that it won’t boot a DU device, so I can’t use it to directly boot the Fujitsu SMD drive connected to the Webster SMD controller.

When booting a TU58 emulator (using the DD command at the “$” prompt), nothing happens for about 10 seconds, and then the boot proceeds normally.

When booting a DY drive, there is an initial “click” from the drive after about 3 seconds. But it doesn’t start to exercise the drive fora bout 15 seconds. I’ve successfully booted from DY0: and DY1:.

This QBUS system appears to be a 22-bit system. I’ve found that I need to use a 22-bit address (17772150) in order to boot into WOMBAT on the Webster SMD board (the 18-bit address 772150 doesn’t work). Here’s the ODT dialog to get into WOMBAT and look at the Fujitsu SMD drive:

[Need to take a log of the dialog and update this]
@17772150/000000 250
@R7/xxxxxx 2000
@RS/xxxxxx 340

WQSMD   WOMBAT Version: 2.8L-4 3 Apr 1991

Unit    Drive   Offset  Size    Type    Shadow  Write   Status
0       0       68      558892  Normal  0       Late    Avail

Drive   Cyls    Heads   Sectors Blocks  Itype   Mtype   Opt  Fair  Status  Dport
0       823     10      68      559640  Std     Fixed   Near  24   spun up  no
Drive number:

As can be seen from the above dialog, it appears the drive capacity is 280MB. In RT-11, we currently only see the first 32MB of the drive.

TO-DO List

  • Make a more accurate list of the boards in this system
  • Provide details and photos of the Fujitsu SMD drive
  • Identify the QBUS backplane (make and model)
  • Map the grant continuity chain in the QBUS backplane