We've just updated MediaWiki and its underlying software. If anything doesn't look or work quite right, please mention it to us. --RanAS
The Prefetch Register is 16-bits wide and not directly accessing by software, but its value can be read via RDVRAML (low byte) and RDVRAMH (high byte). The prefetch register is unaffected by writes to VMDATAL and VMDATAH.