http://pc.watch.impress.co.jp/docs/2005/0602/kaigai184.htm
Hiroshige Goto did an interview with Allard again, this is my translation for the first half. (the second half will be uploaded to PC Watch few days later)
Goto: I'd heard beta devkits for XBOX 360 would be out some time after GDC. Now it seems they are late.
Allard: Devkits are still at the alpha stage (at E3). They are based on PowerPC G5 dual-processor-based systems. But soon (after E3) will migrate to beta hardwares. Beta devkits are very close to the final hardware components.
I think the current completion rate of the system is like that of XBOX 1. At E3 2001 we were still XBOX 1 alpha devkits. So the launch of 360 will be a success just like XBOX 1.
Also, even before supplying devkits, we were trying to offer all info developers need. We are supplying the target spec and migration softwares. As we provided alpha kits earlier, content developments proceed very well. About 160 titles are in development now. A very good figure.
G: XBOX 360 seems to be very costly. For example, the number of memory chips increased from 4 to 8. The GPU die size was 150mm2 before but now a combination of a far bigger chip and an eDRAM chip. You could cheaply procure conservative Pentium 3 for the CPU, but this time 3-core newly designed custom CPU. Is it OK in terms of cost?
A: Your point is correct in a way. XBOX 360 is far more expensive than XBOX 1 for the silicon cost for the die area at launch, though instead the performance is impressive...
Let me explain our approach for this round. The point is, this time, we can pay more cost for the silicon by controlling manufactureing and design more than ever. Silicon cost can be reduced more than anything (in a game console). So it's OK to have expensive chips at the launch. We will be able to make them cheaper (by shrinking them).
In future, the DRAM capacity will be raised, and the process will shrink from 90nm to 65nm or 45nm. We can combine multiple chips on the mobo too. The it'll lead to reduce power consumption and the cost for power supply. So we expect the curve for the price and the cost will be very nice.
G: It's announced that the CPU is a symmetric 3-core CPU. Is this core an equivalent to PowerPC970/G5 or simplified one?
A: Simpler and advanced. Basically we adopted the same CPU core as PowerPC G5. It's based on PowerPC G5, but we removed unimportant features from it. For example instead of having L2 cache for each core we adopted L2 cache shared by 3 cores.
G: In a game console you won't need 2 double-precision ALUs either.
A: Right. Since we don't run general-purpose code, other than those already mentioned there were many features unnecessary for us. After removing them we added some features. For example, we added a crossbar to share a cache, and a special security hardware. Also we refined it to achieve the 3.2Ghz target clockspeed. While the PowerPC G5 chip hasn't reached 3.2Ghz, our CPU can reach there.
G: It's been long since Microsoft withdrew from WindowsNT for PowerPC. Is the XBOX 360 OS kernel is new or is it based on the old PowerPC WinNT kernel?
A: At the beginning of the first XBOX project we ported a part of the NT kernel to XBOX1. This time we ported it to PowerPC. It's not that we went back to the Windows code base. We used the XBOX codebase from the beginning. It's important for developers that they can use the same type of API that they were accustomed to in XBOX 1.
Of course they are not a straight port, the kernel is more advanced. In the XBOX 360 kernel, it supports 6 hardware threads with multiprocess. The I/O system is advanced too. But, even with such enhancements, the XBOX 360 OS is compact and has high performance.
G: IIRC XBOX1 has a small loader in its embedded ROM and loads the OS itself from an optical disc. Where are OS components in XBOX 360? Are they loaded from an optical disc too?
A: This time it's a bit different from XBOX 1. In XBOX 1, it had a file a bit larger than a simple boot loader which is something like a small kernel. In this generation, more technologies are put onto the ROM. For example the networking stack is not on a disc but in the ROM. User interface too. Many important softwares and features are on the ROM.
Basically it's the same strategy that XBOX1 took but in a larger scale. It's one of the goals to make softwares loaded in RAM fewer. However game libraries remain to be shipped on a game disc. It's for the compatibility.
G: AFAICS in the GPU architecture, the graphics API side also has to be extended from DirectX 9. How can you secure the compatibility with PC graphics?
A: It's difficult to completely preserve the compatibility between the 2 platform. There's always a fundamental difference between the PC platform and the XBOX platform. Although, we are making efforts to make them as alike as possible for partners. At least I believe writing a game toward the 2 platforms, XBOX 360 and PC, will be simpler than any other combination of next-gen platgorms. Though we strive to make it as easy as it can be, but hardly free.
G: We heard you'd realize the compatibility between XBOX 360 and XBOX 1 based on software. But performance is largely deteriorated in software emulation. Especially if they have reverse byte-orders like x86 and PowerPC.
A: The solution for the compatibility is partially in the silicon. But the most of it is software. The Microsoft product VirtualPC is an emulater that can run Windows on Macintosh and it runs x86 code on PowerPC. The team that developed it is in Microsoft, so we have some experience on this matter from the beginning. Besides XBOX360 has a very large performance margin. So software emulation is no problem.
Actually, x86 simulation is an easy part if you ask me, as it's emulation of a simple instruction set. Rather than that, graphics, XBOX Live, I/O, these are more difficult to emulate.
G: I suspect graphics will be very difficult as softwares directly reach the hardware in many cases.
A: First we have to suppress the board cost (so can't put a compatibility chip). Because of it, we face the problem how we can deal with different graphics pipes and compression technologies. We allowed game developers to hack the nVIDIA chip in the register level (in XBOX 1). So we had to put some special work for the register-combiner and so on.
G: NVIDIA has patents for things like shadow buffer so ATI can't use them. How can you solve it?
A: For that matter we could an agreement from nVIDIA. It allowed developers to fully use functions they used in the NVIDIA architecture.
It's not only graphics, the compatibility for Live is also very difficult. Especially this time it's more complicated as we integrater Live functions into the core system.
Hiroshige Goto did an interview with Allard again, this is my translation for the first half. (the second half will be uploaded to PC Watch few days later)
Goto: I'd heard beta devkits for XBOX 360 would be out some time after GDC. Now it seems they are late.
Allard: Devkits are still at the alpha stage (at E3). They are based on PowerPC G5 dual-processor-based systems. But soon (after E3) will migrate to beta hardwares. Beta devkits are very close to the final hardware components.
I think the current completion rate of the system is like that of XBOX 1. At E3 2001 we were still XBOX 1 alpha devkits. So the launch of 360 will be a success just like XBOX 1.
Also, even before supplying devkits, we were trying to offer all info developers need. We are supplying the target spec and migration softwares. As we provided alpha kits earlier, content developments proceed very well. About 160 titles are in development now. A very good figure.
G: XBOX 360 seems to be very costly. For example, the number of memory chips increased from 4 to 8. The GPU die size was 150mm2 before but now a combination of a far bigger chip and an eDRAM chip. You could cheaply procure conservative Pentium 3 for the CPU, but this time 3-core newly designed custom CPU. Is it OK in terms of cost?
A: Your point is correct in a way. XBOX 360 is far more expensive than XBOX 1 for the silicon cost for the die area at launch, though instead the performance is impressive...
Let me explain our approach for this round. The point is, this time, we can pay more cost for the silicon by controlling manufactureing and design more than ever. Silicon cost can be reduced more than anything (in a game console). So it's OK to have expensive chips at the launch. We will be able to make them cheaper (by shrinking them).
In future, the DRAM capacity will be raised, and the process will shrink from 90nm to 65nm or 45nm. We can combine multiple chips on the mobo too. The it'll lead to reduce power consumption and the cost for power supply. So we expect the curve for the price and the cost will be very nice.
G: It's announced that the CPU is a symmetric 3-core CPU. Is this core an equivalent to PowerPC970/G5 or simplified one?
A: Simpler and advanced. Basically we adopted the same CPU core as PowerPC G5. It's based on PowerPC G5, but we removed unimportant features from it. For example instead of having L2 cache for each core we adopted L2 cache shared by 3 cores.
G: In a game console you won't need 2 double-precision ALUs either.
A: Right. Since we don't run general-purpose code, other than those already mentioned there were many features unnecessary for us. After removing them we added some features. For example, we added a crossbar to share a cache, and a special security hardware. Also we refined it to achieve the 3.2Ghz target clockspeed. While the PowerPC G5 chip hasn't reached 3.2Ghz, our CPU can reach there.
G: It's been long since Microsoft withdrew from WindowsNT for PowerPC. Is the XBOX 360 OS kernel is new or is it based on the old PowerPC WinNT kernel?
A: At the beginning of the first XBOX project we ported a part of the NT kernel to XBOX1. This time we ported it to PowerPC. It's not that we went back to the Windows code base. We used the XBOX codebase from the beginning. It's important for developers that they can use the same type of API that they were accustomed to in XBOX 1.
Of course they are not a straight port, the kernel is more advanced. In the XBOX 360 kernel, it supports 6 hardware threads with multiprocess. The I/O system is advanced too. But, even with such enhancements, the XBOX 360 OS is compact and has high performance.
G: IIRC XBOX1 has a small loader in its embedded ROM and loads the OS itself from an optical disc. Where are OS components in XBOX 360? Are they loaded from an optical disc too?
A: This time it's a bit different from XBOX 1. In XBOX 1, it had a file a bit larger than a simple boot loader which is something like a small kernel. In this generation, more technologies are put onto the ROM. For example the networking stack is not on a disc but in the ROM. User interface too. Many important softwares and features are on the ROM.
Basically it's the same strategy that XBOX1 took but in a larger scale. It's one of the goals to make softwares loaded in RAM fewer. However game libraries remain to be shipped on a game disc. It's for the compatibility.
G: AFAICS in the GPU architecture, the graphics API side also has to be extended from DirectX 9. How can you secure the compatibility with PC graphics?
A: It's difficult to completely preserve the compatibility between the 2 platform. There's always a fundamental difference between the PC platform and the XBOX platform. Although, we are making efforts to make them as alike as possible for partners. At least I believe writing a game toward the 2 platforms, XBOX 360 and PC, will be simpler than any other combination of next-gen platgorms. Though we strive to make it as easy as it can be, but hardly free.
G: We heard you'd realize the compatibility between XBOX 360 and XBOX 1 based on software. But performance is largely deteriorated in software emulation. Especially if they have reverse byte-orders like x86 and PowerPC.
A: The solution for the compatibility is partially in the silicon. But the most of it is software. The Microsoft product VirtualPC is an emulater that can run Windows on Macintosh and it runs x86 code on PowerPC. The team that developed it is in Microsoft, so we have some experience on this matter from the beginning. Besides XBOX360 has a very large performance margin. So software emulation is no problem.
Actually, x86 simulation is an easy part if you ask me, as it's emulation of a simple instruction set. Rather than that, graphics, XBOX Live, I/O, these are more difficult to emulate.
G: I suspect graphics will be very difficult as softwares directly reach the hardware in many cases.
A: First we have to suppress the board cost (so can't put a compatibility chip). Because of it, we face the problem how we can deal with different graphics pipes and compression technologies. We allowed game developers to hack the nVIDIA chip in the register level (in XBOX 1). So we had to put some special work for the register-combiner and so on.
G: NVIDIA has patents for things like shadow buffer so ATI can't use them. How can you solve it?
A: For that matter we could an agreement from nVIDIA. It allowed developers to fully use functions they used in the NVIDIA architecture.
It's not only graphics, the compatibility for Live is also very difficult. Especially this time it's more complicated as we integrater Live functions into the core system.
