Date: 09 Jun 1993 00:00:01 EST

  Jamie Riotto <jamie@origami.esd.sgi.com> writes:
  An Indigo R4000 has two daughter board expansions which use our
  GIO-32BIS bus design. These cards are about the size of an index
  card.

  An Indigo2 has a 4-slot backplane design. All four slots have EISA
  connectors so you can have a graphics-less server with four EISA
  cards.  Three of the slots have GIO-64 bus connectors, BUT ONLY TWO
  CONNECTORS CAN BE USED SIMULTANEOUSLY!. Graphics board sets take up
  one logical GIO-64 connection, but can take up more physical slots.
  The current Extreme graphics takes up one logical GIO-64 connection,
  but uses three slots. That means the other slot can be used for
  either EISA or GIO-64 expansion. Note that since not all slots have
  both EISA and GIO-64 connectors, you might have to shift the Extreme
  graphics board set up or down a slot if you want to use the fourth
  slot with GIO-64 expansion.

  GIO-64 by the way is similar to GIO-32 but is twice as wide, uses a
  different DMA protocol (pipelined), and used EISA form factor (with
  the connector moved of course :-).