Xerox Alto on eBay

Josh Dersch JoshD at
Thu Apr 14 12:34:03 CDT 2016

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Noel
> Chiappa
> Sent: Thursday, April 14, 2016 10:28 AM
> To: cctalk at
> Cc: jnc at
> Subject: Re: Xerox Alto on eBay
>     > From: Josh Dersch
>     >> They are 12 sector 2315 packs. You have to duplicate it on a two drive
>     >> Alto, since the format is unique.
>     > we're able to duplicate packs and write new ones out from disk images.
>     > (At the moment it's kind of cumbersome -- involving a PDP-11/44 with a
>     > 3mbit Ethernet board, a seriously hacked 2.11BSD kernel and a bit of
>     > luck
> You mean the RK11 controller can write packs that the Alto disk controller can
> read? (As in, the low-level format - preamble, sector header, sector
> checksum, etc, etc are all identical?)

No, they're as different as can be.  The key is that we have a Xerox UNIBUS 3Mbit Ethernet board in the 11/44 (kindly provided by Al.)

I modified the 2.11BSD kernel to support the 3Mbit board (there's already technically a driver but it was incredibly broken and I'm not sure it ever actually ran on a PDP-11), added support for reading/writing raw Ethernet packets using BSD sockets (and added support for that to the DEUNA/DELUA driver as well) and wrote a rough implementation of PUP BSP and the Alto CopyDisk protocol on top of all of that.  It was fun!

So we copy disk images to/from the PDP-11/44 over 3Mbit Ethernet to the Alto :).

- Josh

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