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In my previous article I talked about the Macintosh G4 and specifically the “Digital Audio” model. This time I’m going to talk about another G4 Mac sometimes referred to as a DRR G4 but more commonly known as the MDD or Mirror Drive Door model. Looking at the images above and below it becomes fairly obvious how these machines got their nicknames.

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The case overall is basically the same as the Digital Audio versions case and in fact all the G4 tower PC’s are similar with exception of the face and back. The case color scheme is more silver this time around as well as the cases area of the two drive bays has a mirror like plating, hence the name. This is actually quite reflective and I guess is useful to see if your being snuck up on while browsing on OS X or as a impromptu weapon against Medusa attacks. Also on this mirror finish section we have the power button at the top which glows a nice white when powered on as well as a welcomed frontal audio jack for headphones. The speaker is now placed at the very top with four decorative vent looking recesses at the bottom. Missing are the reset button and programmers button found on the Digital Audio and earlier G4 tower cases.

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The rear of the MDD is the opposite layout of the earlier Digital Audio case. This time the expansion bays are at the top while the various ports and jacks are near the bottom.

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The available ports are exactly the same but in a different orientation. Two USB 1.1 and two Firewire 400 jacks followed by Ethernet and modem jacks and finally an audio output jack and a jack for those Apple high definition speakers. The only addition is an audio input jack next to the audio out.

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Opening the case is the same as before and super easy with a side handle that pulls up and away.

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Inside it’s basically a reverse layout of what we saw in the Digital Audio machine.

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On the section of the case that does not fold out we have two full 5 1/4 drive bays for optical drives as well as a fan and three spots for hard drive mounting. Two 3 1/2 inch HDD bays under the 5 1/4 inch bays and one vertical oriented 3 1/2 inch HDD bay to the left under the power supply. I have two hard drives currently installed. One 80GB drive that holds Mac OS X 10.5.8 and a second 180GB drive for data.

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Like other G4 motherboards the MDD motherboard has quite a few chips soldered on underneath making the board look slightly bare from the top.

1) CPU – The MDD model G4s came with many CPU options up to dual 1.42ghz G4 PowerPC 7455 chips. Mine was the lowest powered model and came with dual 867mhz chips with a 133mhz front side bus. Note that many models in the MDD line came with dual CPUs on a sort of CPU module. As I said previously in articles its hard to compare the power PC to the far more common Intel X86 CPU’s in speed but this would roughly be equivalent to a Pentium 4 or maybe a 1.4ghz Tualatin PIII but this is only a rough guess.

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2) RAM – four slots supporting up to 2GB of DDR RAM which is also why this model is also sometimes referred as the DDR G4. Unfortunately the Power PC 7455 can only use at most 50% of the DRR RAM bandwidth meaning there is no improvement over the previous models and their PC133 SDRAM as far as memory speed is concerned.

3) Four 64 bit PCI slots (which work fine with regular PCI cards) as well as one x4 AGP slot for video. Keep in mind that if your using a x8 AGP card whether a MAC card or a PC card that has been flashed with a mac BIOS you need to disable pins 3 & 11 to get video. This applies to all G4 Mac’s with the exception of the AGP 2x Sawtooth models. This issue is due to apple using the at the time unassigned pins 3 & 11 for the “ADC” apple monitors connection. When AGP x8 came out those pins were suddenly used for something else so basically they wouldn’t run on a G4 Macintosh. The way around this is to disable the pins completely either by taping over them or cutting the traces making the card AGP x4.

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The card I’m using in this machine is a Geforce4 MX. Not a particularly interesting card but it more or less does the job. The MX was a budget card and less advanced then even the preceding Geforce3. For me it’s enough since I really only use this machine for one game and messing with OS X but the MDD G4 can support up to a Geforce 7800 GS with the earlier mentioned Pin modification.

4) Wireless airport adaptor for wireless internet

5) IDE connectors – There are actually three IDE connectors but one is obscured behind the huge CPU heatsink. The one located behind the heatsink is an ATA-100 connection intended for your primary hard drive.

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The two connectors located at “5” are an ATA-66 connector for two secondary hard drives and a ATA-33 that is intended for the optical drives.

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Regardless I have a separate Sonnet ATA-133 PCI controller card installed in my machine for the optical drive and main hard drive while my secondary hard drive is attached to the ATA-66 labeled connector.

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6) CMOS battery used for saving settings.

Upgrading the CPU

I decided to upgrade the CPU in my MDD Mac since the CPU it came with was barely what I needed to do what I wanted to do with this machine. Third party CPU upgrade kits seemed to be overpriced so in the end I decided to go with a cheap $25 upgrade to a single 1.25ghz CPU. Now the value of this upgrade is somewhat debatable since I was going from a dual CPU configuration to a single CPU and OS X can take advantage of dual CPUs but my main purpose of this rig was to play a few select games which didn’t really take advantage of dual CPU anyways so I figured the 383mhz bump was worth it.

When considering a CPU upgrade for any G4 Macintosh keep in mind the CPU modules are not compatible across models so make sure the CPU your looking at is specifically for your model, for instance for a MDD model or Sawtooth G4.

I also wanted to (and needed to with this CPU upgrade) bump the front side bus speed up from 133mhz to 167mhz which required a small modification to the motherboard.

First disconnect any cables from the motherboard and then remove the currently installed CPU which can be done by unscrewing the various screws holding the heatsink on and then gently disconnecting the CPU module from the motherboard. It will look like this with the module removed.

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next unscrew any screws fastening the motherboard to the case and remove. The modification we need to do to enable 167mhz FSB is the desoldering and removal of a resistor on the underside of the motherboard.

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The piece we need to desolder is labeled as R676 and is located near one of the corners of the large black heatsink.

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Desolder this component and that’s it. You can now install a faster CPU and have a slightly higher FSB.

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The final step is to reassemble and install the new CPU. Here is my 1.25ghz G4 CPU module before installation and reapplying the heatsink.

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And lastly booting the machine and checking the system information to confirm everything.

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I like the MDD G4 Macintosh. It’s super easy to work on and plays the few early 2000 OS X exclusive games I need it to play just fine. It does have its issues though. It’s a shame there was no real improvement with the DDR RAM being used over the older PC133 SDRAM. Also upgrading the CPU if you have an early model like mine can be a small chore requiring a modification not to mention the modification needed to use a more powerful AGP video card. Another problem is the fan. This machine can be pretty loud and I noticed it is significantly louder then my Digital Audio model G4. For me the fan isn’t to loud and doesn’t come anywhere near the noisiness of my dual Tualatin rig but I can see how it can annoy some people and the noise level did seem to be a common complaint when I was doing research on the model. I would still recommend a MDD model though if you just wanted to casually mess around with those few early 2000’s OS X games and you can pick up a rig cheaply.

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For this article I’ll be taking a look at my Macintosh 7600 from 1996 but I’m also considering this a overview of the 7500 as well since they are basically the exact same computer using the same case and motherboard. The only difference as far as I can tell besides the case badge is the 7600 came with a slightly more advanced CPU, which since the CPU on these models came on a removable daughtercard you could easily upgrade/downgrade to either or.

Here’s a few pics if you don’t believe me since at one time I had both models.

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I ended up Frankensteining RAM and drives from the 7500 into my 7600 so I condensed it into one machine that I used for some time.

late 90’s Macs are some of the most hated by Macintosh fans but ironically I rather like them, at least in principal. My fondness for them though is the reason many Mac lovers probably dislike them, they are very “PC like”. You can actually easily open and expand a late 90’s Mac unlike earlier models where actually getting inside the machine and tinkering was somewhat discouraged. That said they also share qualities that I hate. chief among them is the plastic tooless cases that although makes it easy to get inside they have not aged well and are very prone to having critical retention tabs snap.

The 7600 is somewhat of a mainstay of late 90’s Macintosh computers and offers decent expansion abilities as well as being pretty easy to work on.

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The 7500/7600 both use the “Outrigger” style case that’s basically a desktop style casing. These models both come with a 1.44mb floppy drive and SCSI CD-ROM drive. To the left of the CD drive bay is room for another drive. When I bought my 7600 off Craigslist it had a purple SCSI 100mb ZIP drive installed in this bay that I promptly removed for another project. To the left of this bay is a built in speaker and below that is a manual power button. Thanks to the brittle plastic my tabs holding the power button in place have broken so it is not always reliable. Thankfully there is a power key on the keyboard.

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I used an Apple Design M9280 ADB keyboard with mine.

The number after the 7600 on the case badge designates the CPU speed that the machine came with stock. Mine came stock with a 132mhz CPU.

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The back features a full range of connections. First from the left we have an external DB-25 SCSI connector. This is followed by two ethernet connector types. First the AAUI or Apple Attachment User Interface, a type of ethernet connector I honestly never knew about before this machine. Next to it is a more standard 10Base-T ethernet jack. Next are two Geoports which are for printer and modem interfaces. This is followed by the Macintosh DB-15 VGA out, of course if you need to connect to a standard VGA monitor adapters are plentiful. Next is a ADB port for keyboard or mouse (your supposed to plug a keyboard in here and then the mouse into the keyboard). Finally we have two 3.5mm minijacks for a microphone and speakers.

Above the ports we have a nice array of video in/out jacks. My models only has RCA stereo out but it does have stereo audio in as well as composite video and S-video in. I don’t really do any editing or work like that much on a Macintosh but these must of been pretty convenient in its day.

There are only three expansion slots as you can tell from the plates on the right but seeing as so much is built in I never found this to be so much of an issue.

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The cover comes off relatively easy. You need to depress two plastic tabs located under the front bezels overhang and then pull forward. With luck your will slide off without anything snapping off. You cant see it here because I removed them but theres is a lot of annoying and flimsy metal shielding across the front drive bays. I have upgraded my machine a little. I replaced the stock 4x SCSI CD drive with a 8x SCSI CD drive from another Macintosh. Macs are very touchy about what drives you use so for simplicity sake I just pulled mine from a Mac from the same era. There are of course ways to get non apple drives to work but for the CD drive I didn’t go through the hassle.

I also added a second SCSI hard drive that you cant see in this image. It is a 2GB IBM SCSI drive. I had to first install it in my other G3 machine and format and initialize it before the 7600 would detect it.

The insides again unfold relatively easily giving access to the motherboard.

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Most of my little tabs and what not have snapped over time. I have to watch the right part of the chassis doesn’t fall down on my hands since the little black plastic stand that props it up also snapped some time ago. With access to the motherboard lets take a closer look.

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1) CPU – Here we have the CPU card. To be honest I like the PowerPC line of CPU’s and I like how easy it is to swap out CPU’s in this fashion. The 7500 shipped with a 100 MHz PowerPC 601 CPU while the 7600 sported a 120 MHz, 132 MHz PPC 604 or a 200 MHz 604e. The front side bus is 40mhz to 50mhz controlled by the CPU card. Mine was originally a 132mhz model but when I received it my machine had been given a 300mhz G3 CPU upgrade. Interestingly my 7500 also had a G3 CPU upgrade leading me to believe these were fairly common upgrades and generally recommended as they seem to really give the Mac some additional power.

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2) PRAM Battery – running without a battery or a low battery seems to have much harsher effects on a Mac then a PC. 3.6V PRAM batteries are relatively cheap and should probably be the first thing to check/replace if your machine is acting odd or unstable.

3) RAM – The 7500/7600 use 70ns 168-pin DIMMs with the standard amount being 16-34MB. I haven’t really expanded mine to much beyond that but the eight slots support 512mb officially and 1GB unofficially with 128mb DIMMS. This is actually a pretty incredible amount of RAM for a consumer computer of the time.

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4) L2 cache – The 75/7600 use a COASt (Cashe On A Stick) module for L2 cache up to 256kb. I don’t know if the machine will support sticks larger then 256k such as 512kb or 1mb but initial research suggests it will. When using a G3 upgrade card such as myself I have read it is advisable to remove the L2 cache stick as the G3 cards have faster L2 cache on the CPU card.

5) ROM – This slot actually confused me for a long time. It’s a ROM slot for some kind of ROM chip which the system I assume would NEED to function yet on both my machines it was not present. It wasn’t until later I found out the ROM chip is on the underside of the motherboard and this slot was left in case any ROM upgrades came later this slot could be used to implement them.

6) Video Ram – Like many Macs the 75/7600 has built in video capabilities. I was not able to find specifics except that at max it supports 1152×870 resolutions at 24-bit and 1280×1024 at 16-bit. The on board video supports up to 4MB of VRAM which is what the four slots are for with 2MB being standard. I was able to lift two 1MB sticks from my 7500 for this machine maxing it out. Keep in mind you need the full 4MB to achieve the highest resolutions. This though is rendered pointless since I did eventually install a dedicated video card.

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7) DAV (Digital Audio Video) slot – This is another slot that took me some time to figure out what it does. Apparently this slot with a cable can be combined with certain expansion video cards. according to here “The DAV connector provides access to the Audio/Video card”s 4:2:2 unscaled YUV video input data bus and associated control signals. By means of a 60-pin cable to the DAV connector, a PCI expansion card can gain access to the digital video bus on the Audio/Video Input/Output Card and use it to transfer real-time video data to the computer. Such a PCI expansion card can contain a hardware video compressor or other video processor.”

8) These are just internal connectors. From top to bottom we have two SCSI connectors, power connector, speaker/CD audio jack, floppy connector and finally 3.3v power connector.

9) The 75/7600 fortunately come with three PCI expansion slots. Adding a video card or two is probably a good choice. There are really no Audio cards made for the Mac to speak of so video upgrade is really your best option. Keep in mind you need Macintosh specific cards. The PCI slots themselves are the same as a PC but the cards BIOS is different. The video card I am using is a RAGE 128 w/16MB of RAM.

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The lack of an AGP slot limits your options but I find the Macintosh Rage 128 cards to be pretty cheap and abundant as well as providing enough power for the majority of 90’s Mac games. You can also add a Voodoo 2 mac edition or if you can find and afford one a Mac edition Voodoo 5500. I actually chanced across a boxed card at a swap meet for $3 once so they can be found.

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So my final opinion? The 7500/7600 can be found pretty cheap and easily off places like Craigslist. I’m running OS 8.5 on mine but they can run OS 7 and 9 without issues according to your needs and wants. With a G3 upgrade and 1GB of RAM these things fly for a machine that came out in 1996. Even with a moderate graphics card like the Rage 128 and a more moderate amount of RAM such as 512MB or even 256MB you should be able to do most of you 90’s Macintosh gaming with ease. The SCSI can be a bit of a hassle though if your not familiar with it and of course replacing drives is more of a hassle. It just makes a nice all around 90’s gaming Macintosh in my opinion and for a time served as my main Macintosh

The toolless cases though as with most 90’s Macs I could do without. It seems kind of cheap and as I’ve said the plastic did not age well and is prone to cracking.

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