Tweak is a hex editor. It allows you to edit a file at very low level, letting you see the full and exact binary contents of the file. It can be useful for modifying binary files such as executables, editing disk or CD images, debugging programs that generate binary file formats incorrectly, and many other things. Tweak supports insert mode (not particularly useful if you're editing an executable file or a filesystem image, but can be extremely handy in other file formats such as PNG). Cutting, copying and pasting within the file you are editing is extremely efficient. No matter how big the chunk of data you are moving around - even if it's a 200Mb section of a CD image - Tweak will always perform the operation effectively instantly. Tweak supports lazy loading of the input file: rather than sucking it all into memory straight away, it simply remembers which parts of the editing buffer are copies of which parts of the input file and refers to the file on disk when it needs to. Tweak only has to take significant time when you genuinely need it to read the entire file. The only two operations with this property are searching, and saving the modified version of the file to disk. Everything else is instant.