OAM buffer. Split into 256 4-word entries, each one representing a possible entry in OAM:
Word 1: Screen-relative X coordinate (low byte copied into byte 1 of OAM low table mirror entry)
Word 2: Screen-relative Y coordinate (low byte copied into byte 2 of OAM low table mirror entry)
Word 3: Copied into OAM low table mirror entry bytes 3 & 4 (see OAM low table mirror $700A00 for details)
Word 4: -p----sx------sx, p = priority (0=forward, 1=reverse), s = size, x = 9th x bit (low byte copied into high table buffer entry)
NOTE: First 16 sprites are reserved for high priority items such as text and these are NOT handled by this buffer, thus copying begins at $700A40 for low table mirror and $700C30 for high table buffer.
Copying will continue until either the last entry of the OAM low table mirror ($700BFC) or the last entry of this buffer ($7009F8).