[WinMac] MACWEEK: G3 upgrade cards unstable?
Dan Schwartz(expresso[at]snip.net)
Mon, 09 Nov 1998 12:08:33 -0500
Dear friends and colleagues:
I just discovered this tidbit about G3 upgrade cards in MacWeek, at:
<http://macweek.zdnet.com/1998/11/02/g3cards.html>.
I used to recommend Sonnet's cards; and I do NOT recommend ANYTHING from
Newer Tech since they don't honor their warranty. For those of you
considering upgrading your 604 Mac, I advise standing by for the moment.
In addition, here are two salient points to consider before upgrading to a
G3:
1) The paragraphs about Adaptec jumped out at me: I have observed serious
incompatibilities with Adaptec's "Power Domain" 2940U-series cards at two
locations with PowerMac 8500/180's. The first instance left the machine
unusable until MacOS 8.0 was released; and the second was a newer
(firmware) version of the card that rendered it unusable even with MacOS 8.0.
It's interesting to note that the "Power Domain 2940U series PCI cards are
*NOT* interchangeable with Adaptec's AHA-2940U-series cards: Although they
conform to PCI 2.01 and up, I was informed by an Adaptec engineer that
there are 3 resistors that have different values for the Power Domain (Mac
PCI) card;
2) Some of these issues with 604 -> G3 cards *MAY* be related to the
firmware (Mac ROM version) in the PCI Mac, i.e. there *may* be differences
between first, second, and third generation PCI Macs (8500/120, 8500/180,
and 8600, respectively; and their corresponding 7500 and 9500 generations).
Be careful!
Dan Schwartz
ORIGINAL ARTICLE:
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November 06, 1998
G3 upgrade cards unstable?
By Cameron Crotty
Installing a G3 upgrade card in an older Mac seems like a great way to get
high performance for a low price, but there may be a tarnish on the silver
lining: An incompatibility between the PowerPC 750 processor and the ROMs
in PowerPC 604-based systems can create serious system instability, and the
consequences range from nonfunctioning I/O cards (e.g. SCSI, video) to
complete system crashes. In extreme cases, the instability may damage or
destroy the data stored on a user's hard drive.
According to industry sources, the problem is difficult to detect and
isolate, but several accelerator card manufacturers, including Newer
Technology Inc., PowerLogix R&D Inc., and Sonnet Technologies Inc.,
confirmed that the incompatibility exists.
Jon Fitch, formerly vice president of engineering at the now-defunct Power
Computing Corp., said Power also discovered the problem while his team was
developing PowerPC 750-based Mac clones. "It took us a long time to track
the problem down," Fitch said. "We had 30 to 40 machines up running around
the clock, and we were getting a 100 percent failure rate."
The systems took as little as one hour to fail or as long as two days,
Fitch said. Power developed a fix for the problem, but Apple shut down the
clone market soon afterward, and the point became moot.
The problem occurs because of "predictive" or "speculative" processing, a
feature found on most modern CPUs. Instead of simply executing commands in
the order received, the processor looks ahead in the instruction queue and
tries to predict which way the code will branch. As part of this operation,
the processor peeks at various memory locations throughout the system,
including RAM, ROM and I/O memory.
Unfortunately, while RAM and ROM are designed to be read multiple times,
certain parts of I/O memory cannot be accessed without altering them. For
instance, some registers automatically reset to their initial state after
being read. This silicon demonstration of the Heisenberg principle -- where
the act of observing an event alters it -- would have no bad side effects
if the processor immediately acted on the data that it obtained. But the
processor is computing predictively -- ahead of the actual code flow -- and
thus frequently doesn't execute instructions in strict queue order. Thus,
it's possible for the processor to change the value of an I/O memory
location (simply by accessing it) without the software being aware of it.
The result is a creeping corruption that can prevent cards from
functioning, completely crash the system or introduce errors in the data
stream-errors with side effects as benign as a video glitch or as malignant
as a corrupted hard drive.
Opinions vary among the accelerator card companies that acknowledge the
incompatibility. Newer Technology said it has known about the problem since
it started working with the PowerPC 750 processors and has developed a
hardware fix -- one that requires about $30 in silicon per upgrade card.
"If you're not using a Newer Technology upgrade card, you're running a
serious risk of losing data," said Darryl Hinshaw, Newer's vice president
of engineering.
Sonnet Technologies agreed there is a problem but said it has a fix in the
form of an extension that loads at startup and tweaks a bit in the memory
management unit to prevent the processor from incorrectly accessing the I/O
memory. Newer disputed Sonnet's claim, saying that fixing the problem when
extensions load leaves the user open to damage during the early parts of
the boot process.
A Sonnet spokesman further claimed that peripheral card manufacturers can
prevent errors from occurring by including synchronization software in
their cards' firmware.
PowerLogix said it also recognizes the problem, but it insisted that,
outside of a few "notorious" cases, the average end user is extremely
unlikely to run into difficulty. Mark Reviel, PowerLogix's vice president
of engineering, said the benefits of fixing the problem would be minor
compared to the cost and delay involved in engineering a solution. "These
problems are nonexistent in G3 Macs," he said. "We may go back and address
it if the market gets stronger, but right now we're more interested in the
future."
On the other hand, Sean Mohle, chief technical officer of Mactell Corp.,
rejected any reports of system-level incompatibilities. He chalked up the
alleged problem to longstanding reports surrounding incompatibilities with
SCSI cards from Adaptec Inc. Mohle further asserted that the reason Newer
Technologies' cards work with Adaptec products is that "Adaptec entered
into a nondisclosure agreement with Newer" so the companies could share
development information -- a relationship not shared by other upgrade card
vendors.
Adaptec could not be reached for comment for this article, but industry
sources said the company is preparing a white paper on incompatibility
issues that will lay blame squarely on the problems with the G3 chip and
604 ROMs.
Dantz Development, another company whose product (Retrospect Remote) has
been affected by upgrade card compatibilities, has gone even further. Dantz
said that it set up a Power Mac 7500/100 (with 32 Mbytes of RAM and running
Mac OS 8.1/8.5) and a Power Mac 9650/350 (with 192 Mbytes of RAM and
running Mac OS 8.1/8.5), each equipped with two different tape drives.
Dantz then tested accelerator cards from PowerLogix, XLR8 and Newer
Technology. According to Dantz Vice President of Marketing Craig Isaacs,
"Newer's cards worked. The others didn't." Isaacs said that while running
the XLR8 and PowerLogix cards, "At between 50 Mbytes and 500 Mbytes of
copying files, the computer freezes. It doesn't happen every time, but it
is extremely reproducible" -- four out of five times.
Isaacs also said Dantz tested the PowerLogix and XLR8 cards with Iomega Zip
and Jaz removable drives. The Macs didn't freeze up, but in roughly 10
percent of the trials Retrospect Remote reported data corruption. "In other
words, either the file backed up is corrupted or the comparison is
corrupted, but either way there's something wrong," Isaacs said.
Dantz said it is completing tests on cards from Sonnet Technologies and
plans to publicly release all results within a week or two.
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