Refurb weekend: Power Mac G4 MDD

I have the very first computer my parents ever bought (a Tomy Tutor, a strange relative of the Texas Instruments 99/4A). I have the first Mac I ever owned, a Macintosh IIsi which was a gift from a family at church; they got it as part of some pallet of stuff they bought and had no use for it. And I still have the first Mac I ever bought new. In fact, now that I think about it, I think this was the first computer I ever bought new.

Here's its sales receipt: a Power Mac G4 DP 1.25GHz (what is colloquially called a "Mirrored Drive Doors" or MDD variant). This was, at least officially and at that time, the last generation of Power Mac that could boot Mac OS 9 natively and the most powerful specification Apple offered that did so. In fact, I bought it specifically for that reason even though I was a starving student and really couldn't afford it because I still had, and have, a big investment in classic Mac applications. I don't remember if I got the education discount, but as specified with dual 1.25GHz 7450 CPUs, 512MB of RAM, 120GB hard disk, 64MB ATI Radeon 9000 Pro and an extra 512MB stick it cost me $3339 before tax in December 2002 (they comped me the install fee). The Quad G5 I bought a little over three years later cost roughly the same out of pocket, so in today's dollars the MDD was actually more expensive. I bought it on an Apple Loan, natch; the Quad I paid for in cash.

The MDD is still connected to my KVM along with my SGI Fuel, Quad G5 and the Raptor Talos II I'm typing on which is my current daily driver. The MDD was my daily driver for about three years, dual-booting Jaguar and Mac OS 9.2.2. Even after the Quad G5 replaced it as my primary machine, I upgraded it to 2GB of RAM (though Mac OS 9.2.2, now its sole operating system, only supports 1.5GB), a 256MB Radeon 9000 Pro and a Sonnet Encore/MDX processor card with dual 1.8GHz 7447A G4 CPUs. It also got a second SuperDrive and a second hard disk, a G4Port serial adaptor to replace the modem which I rarely used and a Formac ProTV tuner/digitizer, and it still has two slots and two more drive bays free. It's not survived perfectly -- the audio jacks got mangled in an accident, so I have to use a USB adaptor for audio in and a set of Pro Speakers -- but the important stuff still works dandy. Classilla is built on this machine, along with my work on Power MachTen and of course all those great late 1990s Mac game ports (though No One Lives Forever, which I bought with it, requires 10.1.4 so I play it on the G5 in Tiger).

On Sunday I was making progress on getting the classic Mac OS to speak TLS 1.3 with a little help (more about this soon). I pressed the power button to transfer my work over and test it and ... nothin'.

MDDs are great machines, but they're notorious for two particular failings: they can howl like anything (nicknamed the "Windtunnel G4") when they heat up, and their power supplies suck. The power supply was undoubtedly what failed, so that means ... a Refurb Weekend!

Ugh, dusty. The Post-It note on the front was to remind me of the Open Firmware path for the internal hard disks. Let's clean it up a little first. (By the way, I hate the speaker grille for these things, so I never installed it.)

The MDD was the last of Apple's "outrigger" Macs. This started with the Power Mac 7200, 7300, 7500 and 7600, and then evolved into the desktop Beige G3 and then reached its zenith with the Blue and White "Yosemite" Power Macintosh G3. These, along with the Power Mac G4, simply open by lifting a latch on the side and the entire motherboard swings down. No screws. Upgrades are a snap.

At this point we paused for a few minutes to blow out all the dust.

Naturally, the power supply (up top) is non-standard, just to be difficult. It is a modified ATX supply (in a weird case that reminds me of the Mini-ITX form-factor, at least in width) with different pinout that in addition to the usual voltages also provides 25V for the Apple Display Connector on the ATI GPU. They came in a 360W Samsung and a 400W AcBel. Fortunately I keep spares, so we will be replacing this 400W AcBel with the NOS 360W Samsung I had in my stock closet. (It is possible to rewire an ATX supply to provide the voltages sans the ADC's 25V line, but an ATX supply won't fit on the shelf inside the case to hold the PSU. We'll consider potential mounting options for the next time this thing chews through one.)

Giving the new PSU a quick test after unplugging the duff PSU's main power connector. You can see the power LED on the board and the fan for the Sonnet upgrade both activate and the Mac "bongs." Time to install it.

The main power connector and the power connector for the accessory drive bay run through the back of the case. This means the optical drives need to be pulled out to access them. Two screws, one at the top front facing the case front and one at the bottom rear facing you, hold the optical drive cage in place. Remove those, take the Faraday panel off the back, unplug the ATA and power cables and set the cage aside.

The main case fan doesn't need to be unplugged, though it might make this easier. Either way, lift it straight up from its little guides and put it aside. The main power cable is now exposed. To remove the power connectors to the hard disks in the rear drive bay, remove the screw from the drive cage's little eyelet (if the screw is there), then find the release lever on its left, pull it towards you and slide the drive cage up just a bit to free it from its socket. Remove the power connectors and, if you like, the ATA connectors as well and set it aside. If you choose to remove the ATA connectors, this is assisted by sliding off the flat black cable clip on the bottom of the case that keeps the ATA cable from bunching up.

A little aperture just in back of where the main fan sits is where the main power and the power lines for the accessory hard disk bay (unpopulated here) are threaded. Pull them out one at a time.

Two screws attach the power supply. The first is a 2.5mm hex screw. This usually needs some cranking to remove and replace.

The second is a Phillips-head screw that bolts a little metal eyelet on the end of the PSU to the case wall. Remove both, slide the PSU from the rear of the case towards the front and take it out.

Install the new PSU and bolt in both the front hex screw and rear Phillips screw. (The hex screw will spin uselessly if it doesn't mate. You need both in because without doing so the PSU will tend to wiggle or shift trying to connect the power cord.) Thread one of the power connectors and the main power connector back in through the rear aperture. Reconnect the main power.

Whenever I have one of my Power Macs open, I always check the 3.6V 1/2AA PRAM battery. This one was, not unexpectedly, dead as a doornail (that's 18.6 millivolts). Fortunately, I keep some of them in stock also.

Replace the main case fan, reconnect the hard disk and optical drive cages, and close it back up.

Back in action. I needn't point out that Mac OS 9 absolutely screams on a machine of this specification.

And just as pretty as ever. I actually do have an Apple Studio Display in storage with an ADC connector I've thought about pairing this with, but fortunately I also have the ADC converter box (basically a power supply that breaks out DVI and USB), so even if I did convert this to some sort of mutant SFF ATX (or SFX) power supply I could still use the Studio Display. In the meantime, I'll see about possibly getting this supply professionally refurbished. I have at least one other in stock along with a full body double but I'd like to keep this trusty machine going as long as I can.

Stereoscopic computing: converting Quake and Doom

This article is part of a series -- you can read other entries

In our first 3D article, we talked about the basics of stereoscopic computing, including anaglyph rendering and active versus passive displays, and demonstrated a tool for turning a twinned set of webcams into a 3D image.

Games, of course, are the most obvious application, but early 3D games mostly dealt with the phenomenon as overlapping 2D planes due to the lack of 3D acceleration, limited CPU power and the predominance of 2D sprite hardware in contemporary video chips. These almost all used anaglyph colours (red/cyan glasses and others), but a few exploited the Pulfrich effect, and we'll look at some examples of these with the Commodore 64 in a later post. Even true stereoscopic systems like the Virtual Boy still largely used scaled planar images rather than true 3D graphics even though their separated video pathways yielded much better results (and eyestrain). As our previous article discussed, we try to avoid anaglyph rendering because all of them have some level of colour distortion (because they use colour differences to deliver a different picture to each eye) and ghosting (because that process is imperfect), and Pulfrich rendering, for reasons we will discuss, has only limited applications. For these examples, we will continue with my trusty Mitsubishi Diamondcrysta RDT233WX-3D, a passive polarized 3D display, though this should work for any passive 3D monitor or television. The general principles also apply to active systems like Nvidia 3DVision, though the details will be peculiar to each particular vendor-proprietary system.

One of the earliest games to have a true 3D mode built into it was id Software's Quake, and, perfect for alternating line polarized passive displays, it interlaced the left and right eye views. However, it was actually created for active glasses alternating between left and right views in sync with the alternating scans of a CRT monitor (here is one such scheme), though this method can still be simulated with a line blanker with modern display cards and LCD panels. This code persisted into early source ports of Quake when id released the code under the GPL, such as in the software-rendered SDLQuake, and is enabled by going to the console and entering lcd_x 1 (the higher the value, the greater the stereo separation). SDLQuake can still, with some effort, be built on modern systems but is strictly limited to 640x480. Naturally, interlaced images will not appear in 3D on a 2D monitor, and may need to be downloaded and moved to the right vertical position to match the polarization order of your screen. For reasons that will become clear in a moment, these were captured during demo playback and could not be paused, but they still serve for purposes of comparison even though the scenes are not exactly identical.

lcd_x 0 (default, 2D only)

lcd_x 1

lcd_x 5

The highest stereo separation yields great effects for most of the display but makes the weapon uncomfortably close, which even without 3D glasses you can tell by how widely spaced the left and right views of it are. For my money the game is really only playable at the lowest separation setting, except that on modern 64-bit systems, SDLQuake and other early releases are not playable at all; they crash immediately when trying to start a new game because they are not 64-bit aware.

Modern Quake ports have corrected this problem but in turn have eliminated much, if not all, of the original stereoscopy support. A few have secondarily added back 3D using alternative means. One such port is Quakespasm, a continuation of the older Fitzquake, which in turn descends from id's GLQuake. Unfortunately, it only has an anaglyph mode (set r_stereo to a non-zero value in the console) and the old interlaced mode is gone. Let's fix that!

Pure software rendering would deal with this problem by taking two images and going to bottom copying one view to odd lines and the other to even lines. A faster approach on systems with SIMD is to blit over one screen entirely using those nice fat vector registers and then line in the other appropriately, which is the approach we took in Camaglyph. However, this is using OpenGL, so we have an additional option of using the stencil buffer. A stencil buffer approach would draw alternating lines in the stencil buffer and then map the left view and right view depending on whether there's a line in the stencil buffer or not. GLQuake does not itself make use of the stencil buffer (too early) and Quakespasm only uses it to prevent intersecting shadows, so we can easily remove that small amount of code to have exclusive control of the stencil buffer since the shadow intersection code is infrequently of rendering relevance.

I don't claim this to be the best way of accomplishing it, but here's my patch against current versions. You will, of course, have to build it yourself from the source code. To enable it, go into the console (usually the tilde key) to set the appropriate options. r_stereo, same here as in regular Quakespasm, sets the stereo separation. I wouldn't make this much higher than 2.0; even that gave me a little bit of a headache, but since it's helpfully a float value 1.5 (in the console, type r_stereo 1.5) is a nice compromise since 1.0 doesn't really have enough depth. To enable interlacing, set the new cvar r_stereomode to either 2 (L-R) or 3 (R-L: my Diamondcrysta is R-L), or set it to 1 for the old red-cyan anaglyph. Because it allows larger screen displays the 3D-enabled Quakespasm is much more immersive and is really quite fun to play. For this screenshot I set the separation to a value of 2.0 so that the effect is a little more exaggerated.

This should work on any system (Mac, Windows or Linux, which is my usual environment) and on any graphics card of vaguely recent vintage.

I mentioned Doom in the title, which is more "2.5D," and mixes flat sprites (characters, objects) with 3D environments. There are many modern ports of this but the one I've come to recently enjoy is GZDoom, which as a built-in feature now has row interlacing as well as many other 3D modes in current releases of its renderer. To do this, pull down the console (tilde key) and enter vr_mode 12. Row interleaving in GZDoom is L-R, so I also add vr_swap_eyes true to make it R-L. You can also add this to gzdoom.ini wherever your system stores it (on Linux, ~/.config/gzdoom/gzdoom.ini). Because it tries to centre the window by default, however, I made a tiny patch to force everything to the 3D monitor which I use as a second, spanned display.

In future articles we will explore 8-bit ways of achieving 3D, and consider an alternate approach for when you want to convert a game to stereoscopic 3D but it's already using the stencil buffer.