The memory controller on the 605 supports interleaving, but the 4mb of onboard ram is not interleaved because it is just 4mb in a single bank.
The RAM SIMM will nearly always span banks and therefore be interleaved. Interleaving can give up to 10-15% speed improvement depending on how it is being accessed.
The onboard video will always come from the onboard RAM (if there is any), so it will always use the "slower" RAM.
You can also see this on the Centris/Quadra 610 and 650's. If you get one with 4mb soldered, it'll be non-interleaved, and if you get one with 8mb soldered, that'll be interleaved and therefore faster.
The RAM SIMM will nearly always span banks and therefore be interleaved. Interleaving can give up to 10-15% speed improvement depending on how it is being accessed.
The onboard video will always come from the onboard RAM (if there is any), so it will always use the "slower" RAM.
You can also see this on the Centris/Quadra 610 and 650's. If you get one with 4mb soldered, it'll be non-interleaved, and if you get one with 8mb soldered, that'll be interleaved and therefore faster.