of the MFT. Advantages Users of fast multi-core processors will find improvements in application speed by compressing their applications and data as well as a reduction in space used. Even when SSD controllers already compress data, there is still a reduction in I/Os since less data is transferred. According to research by Microsoft's NTFS Development team, 50–60GB is a reasonable maximum size for a compressed file on an NTFS volume with a 4KB (default) cluster (block) size. This reasonable maximum size decreases sharply for volumes with smaller cluster sizes. Disadvantages Large compressible files become highly fragmented since every chunk smaller than 64KB becomes a fragment. Flash memory, such as SSD drives do not have the head movement delays and high access time of mechanical hard disk drives, so fragmentation has only a smaller penalty. If system files that are needed at boot time (such as drivers, NTLDR, winload.exe, or BOOTMGR) are compressed, the system may fail to boot correctly, because decompression filters are not yet loaded. Later editions of Windows do not allow important system files to be compressed. System compression Since Windows 10, Microsoft has introduced new file compression scheme based on the XPRESS algorithm with 4K/8K/16K block size and the LZX algorithm; both are variants of LZ77 updated with Huffman entropy coding and range coding, which LZNT1 lacked. These compression algorithms were taken from Windows Imaging Format (WIM file). The new compression scheme is used by CompactOS feature, which reduces disk usage by compressing Windows system files. CompactOS is not an extension of NTFS file compression and does not use the 'compressed' attribute; instead, it sets a reparse point on each compressed file with a WOF (Windows Overlay Filter) tag, but the actual data is stored in an alternate data stream named "WofCompressedData", which is decompressed on-the-fly by a WOF filesystem filter driver, and the main file is an empty sparse file. This design is meant purely for read-only access, so any writes to compressed files result in an automatic decompression. CompactOS compression is intended for OEMs who prepare OS images with the flag of the tool in Windows ADK, but it can also be manually turned on per file with the flag of the command. CompactOS algorithm avoids file fragmentation by writing compressed data in contiguously allocated chunks, unlike core NTFS compression. CompactOS file compression is an improved version of WIMBoot feature introduced in Windows 8.1. WIMBoot