Differences between DDR3 and DDR2 in Burst Length:
Burst Length: Since the DDR3 prefetch is 8 bits, the burst length (BL) is also fixed at 8.
For DDR2 and early DDR architecture systems, BL=4 is also commonly used.
DDR3 adds a 4bit Burst Chop mode for this purpose, that is, a BL=4 read operation plus a BL=4 write operation to synthesize a BL=8 burst of data, which can then be passed. The A12 address line controls this burst mode.
It should also be pointed out that any burst interrupt operation will be disabled in DDR3 memory and will not be supported. Instead, a more flexible burst transfer control (such as a 4-bit sequential burst) will be used instead.