Reading a PDP-11 RL02: Anyone Around the U.S. West Coast?

John Wilson wilson at
Mon Feb 12 00:12:22 CST 2018

On Sun, Feb 11, 2018 at 03:58:48PM -0500, Noel Chiappa via cctalk wrote:
>    > From: Bill Degnan
>    > What is the OS of the disks, what system was this disk used to
>    > create/save files to the RL02?
>Doesn't really matter, does it, as long as the bits can all be read off the
>pack into a file?

Slight gotcha with RLs:  the RT-11 DL(X).SYS driver maintains a bad-block
replacement list at the end of block 1, and uses it to remap the blocks while
it's reading.  Hilarity ensues if you use RT to read a non-RT disk with
junk in that area (or even an RT one if it had bad blocks, since in the
copy, the data have been moved from the remapped blocks to the original
ones so you'd need to nuke the remapping table or RT will try to access
the wrong blocks in the future).  So reading a non-RT RL01/02 (or RK06/07)
disk with .READ(x) isn't safe -- you have to use the .SPFUN call which
bypasses the mapping.  I have a Kermit server which does this.

>somewhere I used to have a program to read DOS disks, but I just looked and
>couldn't find it.)

My PUTR.COM utility can do it, but needs MS-DOS, or an emulation.  Yes I
should finish the portable C rewrite I started ... one of these years.

John Wilson
D Bit

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