Xbox 360: The Guts

We've always gone for brains over beauty, for power over pulchritude, so after oohing and ahhing over the smooth sexy exterior of Xbox 360™, we wanted to know more about what's under the hood. With that in mind, we recently launched a surprise attack on the Lead Mechanical Engineer for Xbox 360, Jeff Reents.

Lead Mechanical Engineer, Jeff Reents.

Xbox.com: What was the biggest challenge about doing the mechanical engineering on this project?

Jeff Reents: It's tougher than the original Xbox® for three reasons. First, we had to pack twice the power of the Xbox into a smaller form factor. Second, it needed to meet much tougher environmental standards. And finally, we needed to be more cost effective.

Xbox.com: Let's talk about the power challenge first. Is Xbox 360 really twice as powerful as Xbox? JR: Yes. Xbox had less than 100 watts of power; Xbox 360 has over 200 watts.

Xbox.com: What are the constraints of packing that power in a smaller case?

JR: Heat, for one. All that power generates a lot of heat, and you have to find a way to keep the unit cool. Fan size was interesting. We originally wanted to put in a single 80mm fan. But we couldn't fit it in the final form factor chassis.

We couldn't just go with one 60mm fan because it would not provide the required cooling—as the diameter of the fan increases the air flow performance per revolution increases exponentially. So we ended up putting in two 60mm fans, and we came up with a water-cooled heat sink as well for the CPU. We've actually applied for a patent on that one.

The water cooled term is being used loosely; actually it is a heat sink constructed of a copper base, aluminum stamped fins and copper heat pipe. The heat pipe contains water and a vacuum is pulled on the pipe prior to sealing.

Water under a vacuum boils at a lower temperature than at atmospheric pressure, so when the water boils and becomes steam, the steam rises and moves the heat higher into the fins where the air flow from the fans can extract the heat more efficiently. Once the steam is cooled it condenses and flows back down the pipe as water to the copper base of the heat sink, which is attached to the processor to continue the condensing and cooling processes cycle.

Dig that sexy water-cooled heat sink.

Xbox.com: Won't two fans make an awful racket while I'm trying to play games or chat or watch a movie?

JR: Actually, we tried to balance the console form factor, thermal performance, acoustic performance and cost of components. With the form factor and system power a fixed specification (determining the minimum airflow requirement and fan size) we use thermal sensing diodes in the main ICs (GPU and CPU) and thermal algorithm firmware that reads the diode temperatures and adjust the fan RPMs by altering the fan voltage to a predetermined minimum requirement that minimizes the fan speed (minimizes the acoustics) while providing the required cooling capacity for the system.

The required cooling capacity of the fans is determined by the system electronics usage scenario; high cooling capacity is needed for intense game play applications, and less cooling capacity is needed for DVD movie viewing. Plus there's the operating environment (ambient temperature and altitude of the console) to consider.

Xbox.com: Good to know. What's the story on environmental standards? Is Xbox 360 "greener" than Xbox?

JR: Definitely. Xbox 360 had to meet the Lead Free requirements and be RoHS compliant.

Xbox.com: I'm thinking that probably has nothing to do with the Rodents of Unusual Size from The Princess Bride.

JR: Uh, no. RoHS is "Restriction of Hazardous Substances." It's legislation enacted by the European Union in 2002 that says all new electronic devices need to meet the standards by July 1, 2006. It's meant to make manufacturers more environmentally cognizant—on a global level.

Xbox.com: Sounds good, but what specifically did that legislation mean for Xbox 360? What kind of compliance criteria did you have to deal with?

JR: It means that Xbox 360 can't contain lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE) or meet the limits established by ROHS. So, the motherboard and all the solder in the Xbox 360 had to be lead-free.

Xbox.com: What other safety features are there?

JR: We have increased radio emissions suppression this time around. The internal metal part of Xbox 360 is the Faraday cage. It keeps radio emissions inside the box. That's why the wireless controller radio has to be outside the Faraday cage, so the signal can escape (radiate). Now, in a perfect world you'd have a completely closed box, so no emissions could escape.

On the other hand, from a thermal standpoint, you want lots of holes to increase airflow. But if the holes have a slot length that is larger than five millimeters in diameter (in our case), excessive emissions can escape. So what you have to do is find a size of hole that will contain radiated emissions, allow maximum airflow and pass the UL Hot Flaming Oil test.

"Hey Bill, check out my airflow."

Xbox.com: Whoa. You lost me for a second, but I'm all over this one. Hot Flaming Oil?

JR: I'll explain: Say you've got a hole size you want to test. You lay cheese cloth under the piece you're testing, and then you take five ounces of diesel fuel and light in on fire and pour it into the holes. The rule is that the cheesecloth can't catch on fire. The fuel needs to self-extinguish before it hits the cheesecloth.

Xbox.com: Damn, where was I during the fire testing portion? Anyway Jeff, let's move on to the cost-saving. How exactly are we saving money on Xbox 360?

JR: Two main ways. We have multiple suppliers for each part of Xbox 360. If you only have one supplier, you have less price negotiation leverage. Multiple suppliers keep the prices competitive. The other thing is that this time we own the IP on the chips. So we can make them at our own foundries.

Xbox.com: Tell me another cool thing about the guts.

JR: Well, we want to discourage hackers, so this time around we didn't put any screws on the outside of the box and have multiple tamper evident labels. So with Xbox 360 we'll be able to tell if they've cracked the case.

Xbox.com: And of course, just like the original Xbox, cracking the case immediately voids your warranty.

JR: Of course.

Xbox.com: Very safe, very powerful, and very cool—inside and out. Thanks Jeff!

More about Jeff Reents:
Jeff grew up in central Illinois, and his first job in high school was a sheet metal punch-press operator. He did a five-year tool and die apprenticeship and majored in Plastics Engineering and Technology at Illinois State. After graduation he worked as an injection mold manager, and in the mid-eighties went to Compaq where he designed and built PCs.

He's been at Microsoft for more than six years. He worked as a mechanical engineer on peripherals and PC hardware. "I was one of the first ten or twelve guys that Todd Holmdahl brought over from the PC side to work on the first Xbox."

• Favorite film: Cool Hand Luke.
• Band he'd like to tour with: Lynyrd Skynyrd.
• Favorite game: Halo®: Combat Evolved.
• Favorite book: John Adams, by David McCullough.