In The Art of Unix Programming, on the topic of The Terminfo Database I read:If you look in the terminfo directory, you'll see subdirectories named  by single printable characters. Under each of these are the entries  for each terminal type that has a name beginning with that letter. The  goal of this organization was to avoid having to do a linear search of  a very large directory; under more modern Unix file systems, which  represent directories with B-trees or other structures optimized for  fast lookup, the subdirectories won't be necessary.I wonder if there are widespread (i.e. production ready) filesystems with this quality.
Are there widespread filesystems which represent directories with structures optimized for fast lookup?
filesystems;directory
There are several, e.g. ext4, Microsoft's NTFS,  Apple's HDF+, or the up and coming btrfs that use B-Trees. There are also HDF and Reiser4 which use B*-Trees, a more densely packed version of B-Tree.