"This interview starts off with Kutaragi offering a reason that the PS3 made use of a specialized graphics unit (GPU) from NVIDIA (the RSX), rather than a GPU based on the Cell processor. 'The seven SPEs (Synergistic Processor Element) of Cell can be used for graphics,' reveals Kutaragi. 'In fact, many of the E3 demos were made without a graphics chip, with only Cell used for all graphics. However, this means of use is wasteful.'
Kutaragi reveals that there was once the idea of using two Cell chips in the PS3, with one used as the CPU and the other used for graphics. However, this idea was killed when it was realized that Cell isn't appropriate for the functionality required for shaders, software tools that are used to draw images to the screen. The decision to go with a separate GPU was made in order to create the most versatile architecture possible.
Backwards compatibility is also on the cards in the latest interview. Referring to the means of backwards compatibility used in the PS3, Kutaragi reveals, 'We use a combination of hardware and software.' While Kutaragi won't specify what hardware components are being brought over from the PS2 to the PS3 (the specs don't seem to reveal anything), he hints that some hardware solutions were required in order to max out compatibility due to the fact that some PS2 games do things with the hardware that are not theoretically possible."