sb magic seg magic segments are static. size? 1/2 meg? 1 meg? what about time corruption? any segment can have a superblock? In Memory --------- segment suage table <- only needed for writes inode map <- need for r/w superblock <- needed for ? ifile on disk has "next" segment #. each flush segment has "next" segment #. superblock has version #. 16 superblocks? block usage bitmap in segment header.