IBM 3725 Communications Controller

Ethan Dicks ethan.dicks at
Thu Dec 14 04:15:42 CST 2006

On 12/14/06, Richard <legalize at> wrote:
> Does anyone have experience with one of these puppies?  There's one
> for dirt cheap on ebay right now, item 170059136469.

I know a _little_ bit about them (we used to have a 3705 on our 4331
at Software Results, c. 1984).

> Its Big.  Its Blue.  Its Heavy.

It is all of that.

If I'm remembering correctly, the 37x5 controllers are SNA PU Type 4
devices (the CPU is a PU Type 5, and terminal controllers like the
3274 are PU Type 2s).  They are Channel Attached to the CPU and,
essentially, aggregate lots of comparatively low-speed I/O channels
and hand data (or take it) in big chunks to (from) the CPU.  You
might, for example, hook a 3274 terminal controller to a 3705 (as we
did) to deploy a quantity of 3270 terminals.  You might also hang a
3780 bi-sync workstation or emulator off of a sync channel of the
37x5, as we did as well.

I really only ever knew about these boxes from their standpoint on the
SNA network.  I've never had to fiddle with the hardware.

If you don't have a full-on IBM mainframe-class CPU, I can't see how
you'd be able to do anything with this sort of box.


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