          Document:  PCI chipsets list
        Maintainer:  Patrick Duffy, duffy@theory.chem.ubc.ca
Last Revision Date:  May 29, 1995
       Archived at:  ftp.netcom.com, in directory /pub/ab/abe/
         Web pages:  http://warp.eecs.berkeley.edu/os2/workbench/work.htm

Here follows a brief summary of PCI chipsets.  I've tried to keep it
accurate, but if you spot any flaws please feel free to correct me, and
if you have details on other chipsets, please feel free to let me know
about them. I've included information at the end of this list to help
people ID the chipset (assuming they have an Intel chipset on their
motherboards).  ID information for other chipsets will be gratefully
received.


                        PART ONE:  80486 Chipsets
                        -------------------------

1) The Aries Chipset
   -----------------

This is a chipset made by Intel for 80486-based machines, and used in
boards (such as the Asus AVP4) where PCI and VL buses are to coexist.
Unlike the Contaq chipset below, the Aries chipset implements PCI using
a PCI to CPU bridge, and the VL bus is attached to this.  This allows
for full PCI performance, though I don't know what effect it has on VL
(which likely will run no faster than the 33 MHz at which PCI 2.0 runs).
The chipset has apparently been through at least two revisions, though I
don't know of any specific problems with either one.

2) The Contaq Chipset
   ------------------

The Contaq 82C599 is paired with one of their 486VL chipsets (82C596 or
82C597) and bridges directly from the 486 CPU to the PCI bus.
Paraphrased from the Contaq spec.:

The 82C596 system controller provides the CPU interface, VESA bus
interface, ISA bus controller, etc. The 82C599 PCI controller provides
the bridge between PCI master/slave agent and the ISA/VESA standard
expansion bus; it arbitrates all the bus transactions between host CPU,
PCI agent, VESA device, and ISA device.

(Which sounds to me like the PCI bus is attached to the VL bus, rather
than to the CPU, which will cause PCI performance degredation.)

3) The Opti Chipset
   ----------------

Components:  82C822 (PCI functions)
             82C895 (all other functions)

This is Opti's chipset for 486-based machines.  It's reported to work
well with OS/2, although it implements PCI using a VL-to-PCI bridge
instead of the other way around.

4) The Saturn Family of Chipsets
   -----------------------------

The Saturn family of chipsets is designed for use exclusively with 80486
and compatible processors, up to DX4s.  They will, as of the latest
revision, work with the P24T Pentium Overdrive processor.  Boards which
use them typically are of the combination ISA/PCI type, as I do not
believe the Saturn chipsets were designed to handle VL extensions.

The Saturn chipset has been through three revisions, numbered (oddly
enough) 1, 2, and 4.  Some brief comments on each:

Rev. 1:  Is now long-since discontinued.  This chipset will only appear
         on older motherboards (perhaps pre Jan. '94?), and should not
         be on any motherboards of recent vintage.  This chipset had
         problems (unknown to me), and so was put through its first
         revision and re-released.

Rev. 2:  Is still in wide use.  This chipset has problems with cache
         integrity during PCI to CPU burst mode operations, as well as
         certain SCSI operations.  Any board which uses this chipset
         today will still have these problems.  There are BIOS "fixes"
         provided by various manufacturers, but what these usually do is
         disable the high-performance options on the chipset.  Rev. 2
         was never 'fixed', and there is no such thing as a newer
         release called rev. 2.  Because of the bugs, however, a new
         version of the Saturn chipset was released.

Rev. 4:  With this release of the Saturn chipset, Intel seems to have
         finally fixed the problems with the earlier revisions.  This
         chipset (also called Saturn II) also supports all the green
         features when used in combination with the right BIOS.  It is
         distinguished externally from its older cousins by the last two
         letters on one of the three chips.  Check for a 'ZX' to
         positively identify the Saturn II chipset.

5) The SIS chipset
   ---------------

Components:  85C496 and 85C497

SIS makes a separate chipset for 486-based boards which is commonly used
in systems which also have VL slots.  Unfortunately, it sounds as though
the chipset implements PCI by bridging it to VL (instead of the
other way around), so PCI-based systems which have VL slots will suffer
a degredation of PCI performance.  Still, however, boards manufactured
by AMI and Asus have been reported to work well with OS/2.  There have
been three revisions of this chipset:

A4:  Had no on-board IDE support.
B2:  Had on-board IDE support, but mode 3 transfers apparently did not
     work well.
B3:  The final bug-fixed version, which now apparently works as it
     should.

6) The VIA GMC chipset
  --------------------

This chipset includes the VIA VT82C486A-F with a built-in 8042 keyboard
controller and a VIA VT82C505-D chipset for the VESA to PCI bridge.
Specifically, the chips are as follows:

82C486A - cache/memory controller + VLB to ISA bridge
82C482 - VLB to ISA bridga (why there are two I'm not sure)
82C483 - DRAM controller
VT82C505 PCI to VLB bridge

A board using this chipset has been unstable (even under DOS/Win), and
did not work with an Adaptec 2940 SCSI controller under OS/2 at all.
Boards based on this chipset are therefore to be avoided.  I have,
however, had one report of success from someone using revision G of this
chipset, so it could be that the new revision fixes problems with older
rev's.

                        PART TWO:  Pentium Chipsets
                        ---------------------------

1) The Mercury Chipset
   -------------------

The Mercury chipset is designed for use primarily with 60 and 66 MHz
Pentium processors (so you won't see 486 motherboards with it, and you
usually won't see 90/99 MHz boards with it either, though there are
always exceptions).  It has, apparently, been through two revisions as
well, though I'm not aware of problems with the first rev. More than
likely the second rev. was just to add support for green features.


2) The Neptune Chipset
   -------------------

The Neptune chipset is designed for use with 75, 90 and 99 MHz Pentium
processors (so you won't see 486 motherboards with it, or 60/66 MHz
boards with it either).  The Neptune chipset has been through two
revisions.

Rev. 1:  This chipset was in boards shipped by Intel to vendors up until
         about the end of July 1994.  It has/had problems with posted
         buffered writes, which would manifest themselves most
         prominently with SCSI devices (which used this feature
         extensively).  Recent releases of the AMI flash BIOS which
         Intel ships with their Premiere II (90 MHz) boards (the latest
         is 1.00.12.AX1) switch posted buffered writes off on the
         chipset when rev. 1 of the chipset is detected.

Rev. 2:  This chipset is in boards shipped by Intel to vendors as of
         about mid August 1994.  It has no reported problems (and works
         well in my system).


3) The OPTI chipset
   ----------------

There are two OPTI chipsets in use:

One is used in Pentium boards which also have a VL bus. This from the
OPTI spec. sheet (paraphrased):

One of the other OPTi chips provides CPU interface, VESA bus interface,
ISA bus controller, etc. The 82C822 PCI Bridge bridges between the
ISA/VESA and the PCI; it arbitrates the bus requests between host CPU,
PCI masters, DMA/ISA masters, and Refresh.  (The other chips in the
chipset are the 82C596 and 82C597.)

(Which again sounds to me like the CPU is hooked up to the VL bus and
the PCI is bridged to that.)

There is apparently a problem with this chipset which causes the
BusLogic and Adaptec SCSI adapters to not work properly, as the PCI
controller is not being properly programmed.

The other OPTI chipset is apparently new and nicknamed "Viper".  I do
not know much of it, except that it consists of the 82C556, 557, and 558
chips.

4) The SIS chipset
   ---------------

SIS makes a chipset for Pentium-based PCI motherboards which will
apparently support (with the right BIOS) some non-spec. PCI operations.
There are settings, apparently, which will allow the PCI bus to run at
CPUCLK/1.5, which means that for a 90 MHz CPU (60 MHz external clock),
you could run your PCI bus at 40 MHz.  What affect this has on
everything else remains to be seen, but the chipset is reported to work
well with the Asus motherboard which uses it.

5) The SIS "Rossini" Chipset
   -------------------------

This is apparently a low-cost alternative to the Triton chipset, as it
operates with up to 66 MHz external clock rates, up to two CPUs,
piplined or non-piplined, synchronous or [conventional] asynchronous
SRAM cache, EDO RAM, dual-port busmastering IDE.

5) The Triton Chipset
   ------------------

This is the latest PCI chipset to come out from Intel, and is PCI
2.1-compliant.  It will also increase PCI-to-memory bandwith from 40
MB/sec (in Neptune) to 100 MB/sec, and features an enhanced ISA bridge.
This chipset is used in the new motherboards by Intel (announced
recently) and the P54TP4 motherboard by Asus.  It also supports EDO RAM,
which will allow access to RAM in a 3-2-2-2 burst rather than the
conventional 7-4-4-4 burst. There is also now a 12 word buffer between
the PCI bus and memory as opposed to the 8 word buffer in Neptune.  The
chipset does not check parity, although parity RAM may be used (without
any benefit) in systems which use the chipset.  Systems which use the
chipset appear to run OS/2 very well.

Useful Information:
-------------------
How to find out your motherboard PCI chipset type and revision:
(Requires DOS support to be installed.)

THE FOLLOWING INFORMATION IS SUPPLIED WITHOUT ANY WARRANTY, EITHER
EXPRESS OR IMPLIED, OF ANY KIND.  UNDER NO CIRCUMSTANCES MAY I (PATRICK
DUFFY) BE HELD LIABLE FOR ANY DAMAGE RESULTING FROM USE OF THE
INFORMATION GIVEN BELOW.  YOU (THE READER) ASSUME FULL RESPONSIBILITY
FOR ITS USE AND THE CONSEQUENCES THEREOF.

The following commands will identify various aspects of your motherboard
PCI chipset.  Type each command as it appears (and press enter, of
course).  I've tested this on my own motherboard and it seems to work.
Under the result column, '-' means that nothing will be shown.  I do not
know what the result codes will be for the Contaq or Aries chipsets, so
please feel free to let me know.

Command               Result          Comments

debug                                 Enter debug.

O CF8 F0              -               Open PCI interface.

I C000                86              Chipset manufacturer ID: `8086' means
I C001                80              Intel, any other value implies the other
                                      bytes are nonsignificant.

I C002                DeviceID_LSB
I C003                DeviceID_MSB    Chipset's ID

I C008                RevisionID      Revision number

O CF8 00              -               Close PCI interface

quit                                  Exit debug.

The chipset's ID can be 0483 (Saturn), 0486 (Aries), 04A3
(Mercury/Neptune), or C557 (OPTI Viper).  For the OPTI chipset, the
Vendor ID will show up as 1045.  For the Saturn chipset, revision 1/2 is
for Saturn I, rev. 4 is Saturn II. For Mercury/Neptune: revision 1/3 is
for Mercury I/II, and revision 10/11 is for Neptune rev. 1/2.  Anybody
who's IDed the Triton chipset please do let me know what the appropriate
responses are.

How to identify which revision of the SIS 486 chipset you have:

My information is limited, but apparently the B2 revision chipsets have
a greek letter "nu" on them, on the third line of text.  I don't know
how to identify the other two revisions, though.
         
So that's what I know, as clearly as I know how to say it.  If you have
any questions or notice any ambiguities please do let me know and I'll
do my best to correct them.
