DEC RL Drives

Home » DEC RL Drives

This page is a collection of notes about my experience in working with DEC RL01 and RL02 drives (and their associated controllers).

Main Resources

The most useful resources relating to DEC RL drives are:

Initial checkout of an RL01 drive

Here is my suggested process for checking out an RL01 drive:

  1. Check that the power is off and there is no data cable or terminator connected to the RL drive
  2. Check that the LOAD and WRITE PROT buttons are OFF (ie – that the front of these switches is aligned with the READY and FAULT indicators)
  3. Turn on power to the RL drive. The white READY and red FAULT lights should immediately illuminate. Approximately 17 seconds after power is applied, the yellow LOAD light should also illuminate and you will hear a “click” indicating that the top lid has been unlocked and you can (if you want to) open it using the slide release catch on the top cover of the drive
  4. Press the yellow WRITE PROT button. It should illuminate yellow
  5. All 4 front-panel indicators should now be ON. If one or more indicators are not ON, the globes may be blown (this is reasonably likely) or there may be a fault with the drive (less likely). Without all indicators working, your task of getting the drive running will be more difficult, so now is a good time to resolve any issues with the indicators
  6. Turn off the power to the RL drive. With the power off, connect the RL drive to a PDP-11, and connect a terminator to the other 40-way connector on the rear panel of the RL drive. Make sure the LOAD and WRITE PROT buttons are in the OFF position
  7. Power up the RL drive (with the PDP-11 still powered OFF). Note that the white READY and red FAULT lights come on immediately, and that the yellow LOAD light comes on about 17 seconds later. At that time you will also hear the “click” indicating that the top lid is now unlocked
  8. Power on the PDP-11. Immediately (within about 0.25 of a second) the READY and FAULT lights should extinguish. The LOAD light should come on about 17 seconds later. If the FAULT light does not extinguish, it is likely that you have a cabling issue (cable around the wrong way perhaps at the Berg connector?) or you have a faulty RL controller board in your PDP-11. The most common cause of the FAULT light remaining lit is that the “SYSCLK” signal (Berg pins JJ and HH) is not getting through to the RL drive for some reason
  9. Put an RL01 cartridge of any kind (VAX, RT-11, RSX, XXDP, unknown) in the drive. Make sure you invert the cartridge lower cover and place it inside the drive on top of the cartridge. Close the top cover to the RL drive. Check that the lid has latched closed (if not, fiddle with the slide release catch on top of the drive, until the drive lid is securely closed)
  10. Press the LOAD button, so it moves to the ON position. The LOAD light should immediately extinguish, and you should be able to hear the RL drive beginning to spin up. If the LOAD light fails to extinguish, check that you have remembered to put the cartridge bottom cover inside the drive
  11. It should take approximately 11 seconds for the RL drive to reach operating speed. When the drive reaches operating speed, the READY light should come on (and it should at this stage be the only light on the front panel). If the READY light does not come on, and the FAULT light comes on instead, check that you have remembered to install the terminator on the rear panel of the RL drive (failing to install the terminator will cause this result)
  12. Press the LOAD button again, so that it moves to the OFF position. The READY light should immediately extinguish. Once the drive has spun down (after about 22 seconds), the LOAD light will illuminate and you will hear a “click”, indicating that you are now able to open the top lid and remove the cartridge

If that process has gone well, try booting the PDP-11 using an RL01 cartridge that has a bootable version of RT-11 on it (if you have one). Alternatively, boot into RT-11 from a different device, and then try an INIT or DIR command on your RL drive.

Initializing an RL01 cartridge

This section assumes you have booted the PDP-11 from a device other than the RL drive.

Initialising an RL cartridge is a very simple process. You don’t need to use XXDP to do so. Instead, just issue the following command under RT-11:


After confirming that you want to proceed with this operation, RT-11 will then prepare the cartridge for use with RT-11. It will report to you the number of “BAD BLOCKS” that were found and re-allocated. Typically this process takes around 25 to 45 seconds, if no bad blocks were found. If an excessive number of bad blocks were found (which may be caused by the drive, rather than the cartridge, being faulty) it may take RT-11 up to 45 minutes to report that the cartridge has too many bad blocks. The FAULT light may or may not be on at this point.

Cable Orientiation

The simplest cable to use to connect a PDP-11 and an RL drive is a BC80J (as used on the RL8A) or a BC80M (as used on the RLV12). These two cables are fairly similar in appearance. Both have a 40-pin Berg connector at one end, and a large clunky “RL-style” (for want of a better description) connector at the other end. The Berg connector typically is marked “this side up” and has marking for the A/B and UU/VV ends of the connector. So it is usually very simple to check that you are inserting the BC80J or BC80M into the RL controller board correctly. The main difference between the BC80J and BC80M is that the “M” version has a braid wire at the Berg end that is to be connected to the PDP-11 chassis. The BC80M cable is shown in the diagram on the right here.

The other common means of connecting a PDP-11 (or VAX) to an RL drive involves a hybrid arrangement consisting of a flat cable running from the RL controller to a bulkhead connector on the rear of the computer, which then connects to the RL drive using a round cable that has an RL-style connector on each side of it. The flat cable has a 40-pin Berg connector on each end of it, and is marked BC06R. It is somewhat more difficult to get this connection oriented correctly because: (a) there are no “this side up” marking on the Berg connectors on the flat cable; (b) sometimes the flat cable has “this side up” stamped on both sides of it!; and (c) it is easily possible to orient the Berg connector around the wrong way on the back of the bulkhead. I have one faulty RLV12 controller which I suspect I damaged by getting this wrong. So here is the process to follow to make sure that you have the cable oriented the correct way:

  • Where the flat cable mates with the controller, orient the flat cable so that the cable sits hard against the PCB. This may or may not result in the red stripe on the cable being on the right-hand side (ie at the end of the female Berg housing that is marked UU/VV). If so, consider swapping the cable ends so that the red stripe is at the A/B end of the Berg housing, if that will work. I suggest orienting the cable this way (ie – with the cable pressed flat against the PCB) so that the cable does not get physically damaged by the underside of the PCB in the next slot above the RL controller
  • At the other end of the flat cable (where it mates with the inside surface of the bulkhead connector), ensure that the conductor that was at the A/B end of the Berg housing (at the RL controller end) is at the cam-lock end of the RL-style connector

Following the above process should result in the orientation being correct (it has worked for three separate and different cable connections that I have tried). However, you proceed at your own risk here!

If you want to be doubly sure, I suggest buzzing out the “SYSCLK+” signal with a continuity tester, to make sure it is going where it should:

  • At the controller end (eg RLV12), this signal originates from Berg Pin JJ. This is according to the usual Berg numbering scheme, which has Pin A at the bottom-left corner. Using the IDC numbering (which has Pin 1 at the top-right corner), this would be IDC Pin 11
  • At the RL01 end (looking into the RL connector that is fitted to the rear panel of the RL drive), this signal goes to RL Pin 30. But this is Pin 30 as marked on DEC’s drawings (see links above) which has Pin 1 at the bottom-right corner. Using the IDC numbering (which has Pin 1 at the top-right corner), this would be IDC Pin 29

Notes about faults with RL drives

I tried putting a “3” white plug in a single-drive RL01 system. With that plug in, I was unable to boot a known good RT-11 V5.3 RL01 pack. When I booted from a DU device and tried to INIT an RL01 pack (with the “3” plug inserted), I got the following error:

DL3:/Initialize; Are you sure? Y
?DUP-F-Size function failed


When I re-inserted the “0” white plug, I was able to boot the V5.3 RT-11 pack just fine, and I was also able to INIT the RL01 pack that I tried previously.

Conclusion: It seems that you can’t use a “3” white plug when the system only has one RL drive attached.

Light bulbs

The RL01 and RL02 drives use a #73 (14V) bulb. These are currently available from element14.

These are not to be confused with the #86 (6.3V) bulb that is used in the RA drives (RA81 etc).