Some Background I am putting together "hacks" for quite a while and successfully worked through a lot of glitches thanks to this great forum! Apple´s case designs always have been "different" than the standard PC boxes and some, like the Power Mac G3 are eye-catching till today, so when I stumbled over a G3 empty shell for a bargain of a few Euros I decided to give it a try and put some new life into it. And here we are: My Hardware Built Most of the PC components have been „leftovers“ from other upgrade jobs, yet good enough for day to day purposes: MSI G41m P25 uATX Socket LGA775 Intel Core 2 Quad 2.6GHz processor Scythe HTC cooler 2*2Gbyte DDR3 RAM AMD Radeon 7750 (Verde chip) SILENT graphic card No name Firewire PCI card (NEC chipset) Samsung DVD writer (bulk) [/SIZE] No name PSU, 450W[/SIZE] 500G Toshiba HDD (2.5´)[/SIZE] 120mm Noiseblocker fan, operated with 5V tap directly from PSU 128G SanDisk SSD (the only component I had to buy in for my built) Power Mac G3 Case Modification The G3 I had available has been an aged empty shell and the upper blue front panel pieces was already missing, so I had to find a blue-isch replacement of some sort, not perfect in color and structure, but working. Maybe an original piece flies my way some other day! Those of you who have tried to fit ATX type of HW into this case may have figured, that there are a few severe challenges: usually the DVD drive collides with the motherboard ATX supply with silent large fans (120mm side panel mount) face to the “wrong side”, so airflow is obstructed, or you have to mount it upside down and worry about the back panel openings no longer fitting. Tray type metal frame under the power supply collides with motherboard CPU cooler hight will collide with tray and ATX supply, so stay as LOW as possible Backpanel opening interferes with audio connectors typically none of the mounting standoffs fit standard ATX positions, you´ll have to place new ones. general airflow through the G3 is not designed to handle 200..300W of dissipation So I opted for some modifications helping the above without killing the looks of the G3 and keeping the fan noise level very low: eliminated the tray metal altogether, yes the frame looses a bit of structural stability, but I can live with this and get unconstraint flow of air. Pushed position of the DVD drive all the way UP and created a custom tray opening around the little Apple logo. (see the picture) I should have taken a GREY front bezel for the DVD drive! Perforated the bottom of the case with a circular grid of holes to mount a 120mm silent fan to help getting fresh air Accepted, that only three of the audio connectors (line in, line out, mic in) are accessible, the other three are covered up. Stayed with a regular no name ATX supply with rear fan, I picked a unit with low noise quality fan though. So the G3 looks almost untouched (front and rear) ! Electronics Rewired the original power button, power light to comply with ATX standard. Extended ATX supply wiring to reach the motherboard connectors also in “service position” , side door fully open. Placed HDD and SSD to the bottom of the case and routed the SATA wiring to be unconstraint for opening the case and still cleanly tugged away. Installation There´s not much to say, follow the guides in this forum, El Capitan is running flawlessly, other than: I had to put in an old nVidia 8400 to get off the ground till I found the appropriate “Verde” kext to enable my Radeon 7750, installed the kext, switched the graphics card and voala, the built is running with the 7750. Even the no name firewire card (NEC chip) worked out of the box and I have successfully used it with external pro audio gear (Presonus Firepod). System Performance Given the type and age of the processor / chipset remarkably well! In fact geek bench and rendering benchmark were almost in reach to my genuine MacPro 5.1 (quad core), so good enough for every day type of work. Noise performance Personally I am very pleased with the result, round about on the same level as my genuine MacPro 5.1., so you notice, that the system is on, that´s it. The ATX supply fan noise (the smallest fan in the mix) is "dominating" the profile. Bottom line I am pretty happy with the net result, will swap in a grey front bezel DVD when I run across it. If you don´t have basic hardware sitting on the shelf like me you will certainly be better off with a state of the art mATX motherboard with integrated graphics and get decent performance at a lower power budget, thus more "compliant" with the constraints of the G3 original case.