OWC Rev.C ROM review


OWC has been shipping, and probably still is
, Rev. C ROM modules for beige G3 Macs of the Rev. A series.
These shipped with a RageII+ graphics chip and with 2 IDE busses, both capable of accepting only one drive each. Rev. B and later shipped with RagePro chips and IDE busses that were master/slave capable, ie would accept 2 devices.

The ROM chip from OWC now adds this feature to the IDE busses and also allows to run their OEM Zif CPU upgrades with copper G3s. I bought such a ROM module for a whopping 82$ including 33$ FedEx shipping, which I really didn't need, but had no other choice. I conducted a few tests with the old and new ROM and here is what I found:


Here first some info on the different modules and how to install it.
Installation is pretty straight forward. Open up your Mac, following all the grounding etc procedures, locate the old ROM module in the ROM slot and remove it. This is admittably a fairly tricky thing to do, since that bastard fits really tightly. You are also not allowed to rock back and forth, since the slot is designed to "operate" only in the vertical direction, and you surely don't want the connector to break off your mainboard.
But there's an easy and efficient trick to speed up the removal a lot. Get yourself 2 wires (isolated) of about 7" lenght or so and bend them into a small J. You'll find that the ROM modules feature 2 holes on each side, were you can fiddle those hooks in. Then pull the shorter end of the J gently through the hole until both ends are on the same height again, forming an U with the ROM module in between. Do this on both sides.
Then twist both ends of each U together, slip you index in the latch and pull symetrically on both sides.
The ROM will come out with a click.
To install the new ROM, all you have to do is put it vertically into the connector and press down firmy on both sides until you notice a soft click when the ROM module snaps in.
Then close you Mac back up, reconnect the power and start it up.

You'll also want to make sure you really got a Rev. C module, in case you didn't get it from OWC.
The Rev. A module has 2 ROM chips dating back to 1997, while the Rev. C module has 2 chips dating back to 1998. Also in the Apple System Profiler you can look up the ROM revision:

  • Rev. A has revision number "$77D.40F2"
  • Rev. C has revision number "$77D.45F1"


The Tests

My old beige G3 has been running for almost 2.5 years now, all very stably (except in Quake 3, of course) and rarely needing any service, that's also why my HD is in a pretty messy state, of course hitting performance quite a bit, but I'm too lazy to defragment it etc. All tests were conducted under the same conditions, after a restart.

ROM Revision:
Mac OS 8.6
MacBench 5.0
Norton System Info 4.5
Quake 3
Publishing Disk
Rev. A
Rev. C

There was no effect on graphics or CPU/FPU performance, although, the new ROM resets my screen once at startup, where the old one didn't, but as it seems, startup times are a bit faster and, oh horror, disk performance seems to drop quite a bit in MacBench's Publishing Disk test. I consider the other differences a pure accident, also Quake 3 never reports the same FPS twice.

Master/Slave mode

Now why did I buy that thing anyway? I wanted master/slave capability.
I connected a 2 device IDE cable to my HD IDE bus and attached my original WDC Caviar 36400 as amster and an old IBM DALA 3540 as slave (you can look up your jumper specs on IBM's website).

After a reboot and updating of the drivers on the DALA, the drive mounted like a champ, no problems whatsoever. However, I had planned to install the drive on top of my Floppy drive, the same way I had done so with an IBM DNES SCSI drive on to of a Zip (see here), and found that the DALA is too fat to go in between that space. The space between case and floppy is only about 1.8-2 cm high and a normal HD is 2.3-2.4cm.
It could be done with some grinding on the drive sledge etc, but that really is too much effort, especially because that will also dealign the Floppy cover slot, forcing you to leave it open (and really ugly).
However there are extra flat drives who are only about 1cm high or so, and these would fit in just fine.
I'm yet thinking of options, and I'll let you know if I find any.


If you have some space left in your case and want to add one or more IDE/ATA drives this upgrade is a must. But if you have added SCSI drives before and don't have any space left, stick to your SCSI drives and save the 82$ for an UW/SCSI PCI card or so. The performance drop with the Rev. C module may have been a twist of fate, and in case it is not, most of you probably will never notice.

Update: OWC now also ships Rev. B ROM modules which offer the same functionality. The price has also been reduced to 35$. I have not tested one of these yet, but I think there is no significant difference.

Text: © by Bensch Blaser, Jul. 2000, all trademarks are property of their respective owners.