fun for the EE guys (board design)

Gerhard Lenerz mail at
Sun Jun 11 14:54:29 CDT 2006

Sunday, June 11, 2006, 9:27:08 PM, you wrote:

> Huh?  Perhaps you mean that the way the board connects to
> the rest of the machine is *through* the cables (i.e. there
> is not some other set of connectors on the board that plug
> into a "backplane")?  So, *normally* the cables plug into the
> memory board but, on the last board, the terminator sits
> "between" the cables and the board?

It actually does both. The IRIS has a Multibus backplane into which
all boards plugged. In addition to that for some busses ribbon cable
connections are used. So a look into the cardcage of an IRIS shows
some boards hidden by quite a lot of ribbon cables:

As the leftmost board in that picture you see the memory board along
with the terminator installed. The following boards also connected
by the two ribbon cables at the upper left corner are FPU and CPU. The
reason for the termination not being on the memory board itself is
that additional memory is installed by using further boards. The last
one (leftmost) is then terminated as shown.

Just for another view I also upload a picture of a pulled memory board
(with attached terminator):

Best regards,
 Gerhard                            mailto:mail at

Old SGI Stuff             

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