The design of our capability format was guided by studying the properties of the AdvFS file systems at our 30-person research laboratory. Recall that a capability includes a fixed-size list of extents, which are contiguous ranges of physical blocks. Files occupy one or more extents; for example, /foo/bar might occupy blocks [243-256], [9323-9992], and [20-50]. In our file systems, a single extent covers, on average, 150 KB. Moreover, it turns out that 90% of files require four or fewer extents, and that 95% require 13 or fewer extents. Hence, we decided that any single capability would have space allocated for four extents. Files with more than four extents can be accessed with multiple capabilities.