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Quadra 950: CPU/RAM Upgrades and Overclocking

When it comes to upgrades, the Quadra 950 has 16 SIMM RAM slots, 4 VRAM slots, a ROM SIMM slot, 5 Nubus slots and a PDS slot. RAM and CPU upgrades can be purchased via off-the-shelf means. Little is it known that you can also then overclock your CPU. Below lists some options for getting more horsepower out of your vintage Macintosh.

Apple PowerPC Upgrade Card

The previous owner already had the "Power Macintosh Card" Control Panel installed on the 7.6.1 system. After inserting the card, I went into the control panel and enabled the PPC Card. I was informed that a reboot was required and promptly did so. It rebooted.... Apple System Profiler indicated the same-old 68k processor? I had recalled online that one user had issues with the card, but then found that it wasn't seated properly. Trying this, I shut the machine down and then put the case on its side. A gentle downward press on the card from both top corners resulted in a rewarding click. Nothing sharp, but that feeling of success when you know something is now in the correct location.

I hit the power button and ... jeebuz.... what was that wretched chime? The 68k boot chime of the Quadra 950 is pleasant, if not downright triumphant. The chime that came from the PPC addon card was ... it sounded like a cheap knock-off MOD compared to an MP3. A dodgy, poorly-recorded sample. Either way... it worked. The screen then came on and I could actually see it drawing the background line-by-line as the grey pattern loaded. Then I saw it draw the MacOS central loading screen. I was running the Supermac Spectrum/24 PDQ+ at this point and that turned out to be the cause. It needs a software update. Meanwhile the onboard video performs much better.

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Overall the UI seems much zippier with the PowerPC enabled. Placebo probably... I'll try and perform benchmarks once I have new HDDs and a fresh operating system. Maybe some more RAM too... In the meantime, here's some benchmarks done by Low end Mac.

I've read here at Apple Fool that you can actually remove the 68k CPU when running the PowerPC PDS card. Doing so also resolves graphics issues with other Quadra models. When overclocking (the only reason I found out that you could do this), removing the 68k CPU actually allows you to run the PPC upgrade at faster speeds!

Upgrade VRAM to 2mb

The Quadra 950 has 1mb of VRAM onboard. There are 4 slots in which 4 256kb SIMMs can be installed to extend the video memory to 2mb. This will allow 1152x870 @ 24-bit colour, which is comparable to any video card you can insert! Apple has a support page describing the options for each Macintosh model and you can see that the Quadra can only take 4 more SIMMs.

Four slots support 256k 80 ns VRAM SIMMs for a maximum total of as much as 2 MB of VRAM. 512k VRAM SIMMs can be installed, but four identical ones must be installed and the system can only use 256k of each SIMM.


I initially thought that there was a cache slot next to the RAM slots on the logic board. If you look at the images below in the RAM upgrade topic, you'll see that, apart from the 16 SIMMs for system memory, there is another empty slot top-right. It's near the CPU, so cache made sense. It turns out it's a ROM SIMM slot, not a cache slot. In this slot you can put in a ROM that will override the on-board ROM.

Doug Brown makes ROM SIMM programmers that can write the SIMMs that'll fit into this slot. It doesn't seem that anyone, at all, on the internet has ever done this to a Quadra 950. I've been told that you can change the start-up tune and disable the memory check, if you want to... otherwise your options for profit from tinkering with the ROM are little. It would require some very low-level detailed hardware knowledge also!

But for fun, check out Doug's post where he changed his Macintosh IIci start-up tune to the Super Mario theme. If you do want to code ROM SIMMs, Doug has his ROM SIMM burner for sale here.

This slot does have me thinking... minimal OS on an 8mb chip... it'd be like loading from an SSD!

Cache Upgrades

Meanwhile, you can buy Nubus cards full of cache. These 'MicroMac Cache cards' come as PDS cards or 'slot-free', the latter being a device that is installed between your CPU and logic board. This piggy-back mechanism puts the cache right next to your CPU and keeps your PDS slot free for a PPC upgrade.

Upgrade System RAM to 256mb

This one was simple... purchase from seller in the US on eBay. Wait. Open package. Open Quadra 950. Remove old SIMMs. Install. Or so it should have been... quite the initial scare when, upon applying power, the machine didn't start. It powered, the CD-ROM was eject-able, but it just sat there! around 2 minutes later the grey screen came up. It seems that the machine is busy checking the RAM.

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Further cold starts took just as long; it seems the RAM checks occur every time you boot after a shutdown.

Installing large amounts of RAM in 68k Macintosh computers causes VERY LONG BOOT TIMES. It seems the BIOS runs a memory check and the more RAM in there, the longer it takes. The Quadra 950 with 256mb of RAM now takes 5 minutes from chime to gray happy mac! Note that restarts are as quick as ever.

Now that I've got my RAM in there, it's time to use it with A/UX.

Power Supply Fan

Every now and then, the Quadra would start up and the fan would make terrible noises... It sounded like something was actually stuck in it, but I couldn't see anything. Either way, I managed to take a fin off the fan propeller during an attempt to stop it. I now had to replace it. It's a standard 120mm 12v fan and a replacement was easy to find.

As I pulled off the old fan, I found the cause of the previous noises! There was an unused cable-tie in there. It seems that it had either been sucked in, or someone had shoved it in there. It was not damaged and did not come from inside the power supply. Every now and then it'd make its way close enough to the fan blades to make a racket. Seems that a bump would make it quiet again, but it would've been entirely random!

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Either way, the new fan was in place with some adjustments; it was around 10mm shallower. The previous fan was also powered by the socket on the power supply. I grafted the new fan onto the old fans plug. The system is now running 'cool' again and much quieter! I even get a pretty blue light inside the case.

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Overclocking your Quadra 950

Lowend Mac has the downlow on this. With the PPC card installed, I could max my oscillator out at 80Mhz. The system would then run the 68040 at 40 MHz and the PPC card at 80 MHz. Note that there may be software incompatibilities once you upgrade. Check out Apple Fool's run-down of incompatibilities here. For further information, check out Mac Crystal Oscillator Speedup History 2.6. Note, you may not be here for the Quadra 950, check out the Apple Fool Machine Specifics page to see the recommended crystal for your machine.

Based on the modification options table at Apple Fool, the Quadra 950 can take option 1 or option 2. Option 1 sounds the easiest whereas option 2 the safest... either way you need a soldering iron and some guts to tinker with your vintage macintoshes logic board.

The oscillators are available on eBay for a few dollars. I purchased mine from a Hong Kong seller. I bought a 5pk just in case. The are a standard-size unit and have 4 pins. The existing components are soldered into the motherboard, so from here on in you're in for a challenge. The best bet is to unsolder the current crystal and solder in a socket. This will allow for easy replacement to the original crystal if problems are encountered.

It might be hard to find an exact socket for the crystal. Jaycar has 14-pin sockets but they have all pins when we only want the four corners. I've modified a full-size socket by pushing through the intermediate pins.

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The sockets are a mongrel to manipulate. Firstly, break off the thin end of the pins to be removed. They only bend when you try to force them out, so remove them from the equation. Next, use pliers or find a surface with a suitable space to push the other side of the pin in to. You could use hammer and nail here, with the head of the nail on the pin. Tap them out gently, but be warned, they are in there solidly and will require a bit of work. I used pliers on them, at an angle, and squeezed them out; but not without minor damage to the housing.

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Removing the logic board is straight forward. Remove all the cables from the rear, remove any Nubus cards or PDS PPC card installed. Remove the power supply and hard disks/floppies/cd-roms. Disconnect the speaker and the power switch cables. The debug and reset buttons 'pop out' and can hang half out the front of the case during the process (see pictures.) There is then a tab between the memory banks, to the left, that needs to be pushed down. Once down you just need to slide the whole logic board left and it'll fall into your hands.

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Once out, heat up your soldering iron. You'll find the 66.6mhz crystal directly above the 68040 CPU. There's four pins on the back that needs to be de-soldered. Your process will either be to (as I did) loosen them one at a time, jimmying the crystal off the board, or the smarter way: use a solder-sucker to remove all solder from the pins and hope that the crystal will just slide out.

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Either way, it took me around 10 laps of the pins with a very gentle lever-action in between to remove the crystal. I then soldered my socket in, not doing the cleanest job!

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powerpcI put the original crystal in the socket (keep the 'pointy' corner of the crystal in the top-right corner!) to test that the socket was good. Note that the original crystal will have very short legs! Make sure that it's in as-firmly-as-possible and that you don't bump the machine and dislodge it! Running benchmarks (more on this below) produced the same results as pre-chipping. We win. I then shut down the machine and socketed the new crystal. It was a very suspenseful wait for the RAM checks to happen... was the machine going to boot??

5 minutes later.... I had an 80mhz PowerPC 601 machine~!

Benchmarking MacOS

Speedometer is included with the Newer Technology Disk downloads. The results, pre-clock-chip, are as follows:

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After the chipping, the following results were produced:

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Yeeeeey! Not only did the bloody thing boot, the speed increased! It seems round ~20% too. Makes sense really... since the previous crystal was 66.6mhz, with the new being 80.0mhz.

SieveAhl is a recommended benchmark application for 68k Macintoshes. This application performs two tests: Sieve and Ahl. Pre-clock-chip results are reported below. The 500 tests executed very quickly. The site has a disclaimer that running the tests on PowerPCs isn't accurate as they use all sorts of emulation layers to execute 68k code. Either way, I have a clean set of figures pre-chipping.

sieve-download sieve-pre-chip-1 sieve-pre-chip-2

After the chipping the results were as follows:

sieve-configure sieve-post-chip-1 sieve-post-chip-2

...there's that ~20% increase again! Winner... the overall OS felt much zippier.

Over-clocking equals over-heating!

Of course, your mileage will always vary when over-clocking anything. Extra speed always leads to extra heat and then compounds into stability issues; the system was clocked at a specific speed by the manufacturer after rigorous quality control. Unless politics/marketing have come in, then higher clock-speeds have proven to be unstable and therefore weren't selected/enabled. Don't be sad that your CPU created a nuclear event, be happy that you had it rocketing along for a few nanoseconds! Of course, try and keep it cool for as long as you can.

It turns out that the 20% speed increase also increased the heat coming from the CPU. After around 30 minutes of running, depending on what I was actually doing, the machine would freeze. This is a very common symptom of overheating and the best method is to air-cool the CPU. The PowerPC PDS Card has a heatsink on it, but it's only passively-cooled. Fitting a fan to this should help keep the temperatures down.

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I grabbed a fan from a local PC store that plugs into the standard power cables. It was a little huge for the scenario, but it kept the CPU nice and cool during normal usage. Note that there ain't much clearance in the case with a fan of this size... if you need more than 2 nubus slots then you'll want a smaller fan that fits inside the heat-sink fins.

If you've successfully over-clocked your 68k then fill out the survey at Apple Fool to keep everyone informed. You can see the results of other successful chippers here.


About stevenh

Trains... trains... trains... + Electronics + Japan.
Comments (3) Trackbacks (0)
  1. You know, I’ve always wondered if it was possible to use the quaddoubler in the 950. From my understanding the only changes between the 900 (which fully supports use of the quaddoubler) and 950 were the clock speed and and slightly faster integrated graphics. Of course the quaddoubler runs at 50mhz (55 through overclocking) and requires a 25mhz stock cpu, much slower than the 950’s 33mhz. This adds the ironic twist of underclocking the 950 for compatibility, which in turn will give it speed. But then again, if one will go through all this effort one might as well buy a 900, install the quaddoubler and a NuBus graphics card (to get around the slower video) and then be done with it.

    • 3371-Alpha,

      I was assuming the upgrade would be via the PDS slot. But the QuadDoubler seems to be an entire CPU-replacement kit? You actually get a tool to remove the existing 68k CPU?

      You can see above that this CPU is indeed socketed, so one would guess that you could put an 040 in here.

      Unfortunately I no longer have the machine, so wont be able to try the theory out.

      • Yep, it’s a full cpu alright. There’s even a version with a built-in 128k cache. I also believe MicroMac has a similar product called the SpeedDoubler040 which is similarly for only the Quadra 900 & 700, though it is worth noting that some people have had issues with other MicroMac products (i.e: ).

        It’s a shame you got rid of 950. Though not the fastest 68k machine, it certainly was the most expandable.

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