William Swearingen, Director of Strategic Communications at Motorola, told MacCentral that the G4s driving Apple’s new G4 mini-tower systems are indeed the long anticipated Apollo processors. Labeled MPC 7455 and MPC 7445, the Apollo G4s achieve all of the goals that Motorola outlined at the 2000 Microprocessor Forum — namely GHz+ performance, fabrication using SOI (Silicon On Insulator) technology, the ability to have a 2MB DDR (Double Data Rate) L3 cache, and a superior power consumption/performance ratio.
It is important to note that this is only the first installment in this processor family. “The big news here is that this device is certainly not topped out,” said Swearingen. Mac users can reasonably expect incremental performance increases from this processor family in the future, taking Apollo to its promised GHz+ performance levels. Swearingen could not comment on when these increments will come or what size they will be. The Apollo G4s are available now at speeds between 600MHz and 1GHz.
When examined in detail, the Apollo is similar to the G4s that Apple used previously. This is no surprise, as the new processor was specifically designed to be pin-compatible with the previous generation G4s. This is good for Apple and other vendors who use the part, as no additional design work is necessary to allow the Apollo to work in an existing design.
The Apollo has four integer execution units, one double precision FPU, and four 128-bit AltiVec execution units — again identical to the G4 Apple used in its previous models. The Apollo also sports a 256KB on-chip L1 cache — just like the previous G4. The Apollo is also fully symmetric multi-processing capable and compatible with the 133MHz 64-bit MPX bus which previous G4s used.
However, things begin to change with the L1 cache. The Apollo adds cache-locking instructions to allow critical instructions or data to be locked into the cache for a performance benefit. With the L2 cache, the Apollo allows up to 2MB of DDR RAM to be used. DDR RAM allows data to be sent or retrieved on both the upswing and downswing of the clock cycle, essentially doubling the bandwidth over conventional RAM.
The big change with Apollo comes with its manufacturing. The MPC 7455 and 7445 are manufactured using a 0.18-micron copper fabrication process that takes advantage of SOI technology. SOI is the addition of a thin layer of silicon between the transistors on the chip and the non-conductive base or substrate of the chip. This layer reduces the capacitance, or the necessary time and amount of energy, needed to close the gate. The use of SOI on every transistor on a processor allows the processor to run faster, consume less energy and generate less heat.
As noted above, the Apollo is labeled as MPC 7445 and MPC 7455. The 7455 is thus far the only Apollo used by Apple. The 7445 core is essentially identical to the 7455 except that the 7445 is intended for lower power consumption applications and has no connects for an off-chip L3 cache.
While not essential for Apple, low power consumption is important for all of the other manufacturers who use G4s. At 1GHz, the 7455 typically dissipates about 20W of heat. At 600MHz, this drops to around 10W. To compare, a 1GHz AMD Athlon typically dissipates around 50W of heat. Swearingen said that the Apollo’s low power consumption and heat dissipation is very helpful for OEMs. “Using SOI, we have created a processor that can sell across a wide range,” said Swearingen.
Motorola’s news release about the Apollo yesterday contained mention of Apollo design wins within the networking, mobile communications and embedded markets, but no mention of its win with Apple. Swearnigen said that it was essential that Motorola did not pre-announce Apple. “In working with them [Apple], we had to be sure that we didn’t steal Apple’s thunder. When a customer is as strategic and important as Apple, we don’t mind helping their publicity efforts,” said Swearingen.
Swearingen said that Motorola is committed to its PowerPC roadmap, but would not comment on any future developments with the G4 or any proposed G5 computing processors. However, with the introduction of the Apollo, the only item left on the G4 portion of Motorola’s PowerPC roadmap is a migration to a 0.15-micron manufacturing process.