sectors, disk rotation speed, head speed, and alignment of the sectors between tracks. In a fully optimized system, the head could be moved between close tracks to read scattered sectors from alternating tracks while waiting for the platter to spin around. As disks grew larger and larger, sector-level optimization became obsolete (especially with disks that used linear sector numbering and variable sectors per track). With larger disks and larger files, fragmented reads became more of a problem. To combat this, BSD originally increased the filesystem block size from one sector to 1 K in 4.0 BSD; and, in FFS, increased the filesystem block size from 1 K to 8 K. This has several effects. The chance of a file's sectors being contiguous is much greater. The amount of overhead to list the file's blocks is reduced, while the number of bytes representable by any given number of blocks is increased. Larger disk sizes are also possible, since the maximum number of blocks is limited by a fixed bit-width block number. However, with larger block sizes, disks with many small files will waste space, since each file must occupy at least one block. Because of this, BSD added block-level fragmentation, also called block suballocation, tail merging, or tail packing, where the last partial block of data from several files may be stored in a single "fragment" block instead of multiple mostly empty blocks. The work on Berkeley FFS was widely adopted by other Unix vendors, and the family of filesystems derived from it are collectively known as UFS. Implementations Vendors of some proprietary Unix systems, such as SunOS / Solaris, System V Release 4, HP-UX, and Tru64 UNIX, and open Unix derived systems like illumos, have adopted UFS. Most of them adapted UFS to their own uses, adding proprietary extensions that may not be recognized by other vendors' versions of Unix. Many have continued to use the original block size and data field widths as the original UFS, so some degree of read compatibility remains across platforms. Compatibility between implementations as a whole is spotty at best. As of Solaris 7, Sun Microsystems included UFS Logging, which brought filesystem journaling to UFS, which is still available in current versions of Solaris and illumos. Solaris UFS also has extensions for large files and large disks and other features. In 4.4BSD and BSD Unix systems derived from it, such as FreeBSD, NetBSD, OpenBSD,