OS X 10.3 also marked Apple's adoption of Unicode 3.2 decomposition, superseding the Unicode 2.1 decomposition used previously. This change caused problems for developers writing software for Mac OS X. Mac OS X 10.3 introduced a number of techniques that are intended to avoid fragmentating files in HFS+. With Mac OS X 10.4, Apple added support for Inline Attribute Data records, something that had been a part of the Mac OS X implementation of HFS Plus since at least 10.0, but always marked as "reserved for future use". Until the release of Mac OS X Server 10.4, HFS Plus supported only the standard UNIX file system permissions; however, 10.4 introduced support for access control list–based file security, which provides a richer mechanism to define file permissions and is also designed to be fully compatible with the file permission models on other platforms such as Microsoft Windows XP and Windows Server 2003. In Mac OS X Leopard 10.5, directory hard-linking was added as a fundamental part of Time Machine. In Mac OS X Snow Leopard 10.6, HFS+ compression was added using Deflate (Zlib). In open source and some other areas this is referred to as AppleFSCompression or decmpfs. Compressed data may be stored in either an extended attribute or the resource fork. When using non-Apple APIs, AppleFSCompression is not always completely transparent. OS X 10.9 introduced two new algorithms: LZVN (libFastCompression), and LZFSE. In Mac OS X Lion 10.7, logical volume encryption (known as FileVault 2) was added to the operating system. This addition to the operating system in no way changed the logical structure of the file system. Apple's logical volume manager is known as Core Storage and its encryption at the volume level can apply to file systems other than HFS Plus. With appropriate hardware, both encryption and decryption should be transparent. Design HFS Plus volumes are divided into sectors (called logical blocks in HFS), that are usually 512 bytes in size. These sectors are then grouped together into allocation blocks which can contain one or more sectors; the number of allocation blocks depends on the total size of the volume. HFS Plus uses a larger value to address allocation blocks than HFS, 32 bits rather than 16 bits; this means it can access 4,294,967,296 (= 232) allocation blocks rather than the 65,536 (= 216) allocation blocks available to HFS. When disks were small, this was of little consequence,