If you ever accidentally open an exe program file in a text editor such as Notepad, you will be confronted with a mass of unintelligible garbage on your screen. Worse still if you write the exe file back to disk, the program file would almost certainly be corrupted and would not work.
That's because text editors are designed only to work with text files which are files with extensions such as .txt, .bat, .prg and .html. To view and safely change binary files such as .exe, .com and .dll files you need a hex editor, sometimes called a binary editor. Most average PC users have no need for such a program but techies and gamers find them indispensable.
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There are some excellent free hex editors available that range from the small and simple editors to advanced products that are comparable to any commercial product. Hex editors are a software category where personal needs and preferences are so important that it is meaningless to pick a "best product". That of course doesn't stop me stating my own preferences.
For my needs, HxD is a clear winner. Its first virtue is that it doesn't need installing. Second, it has a great interface. Third, it handles huge files without slowing down. Then add in unlimited undo, great searching and search/replace capabilities, binary file comparison, full support for ANSI, DOS/IBM-ASCII and EBCDIC character plus a dozen other features and you can see why I like it. But it doesn't stop there. Hxd also works as a RAW disk editor and a full read/write RAM editor. This power also makes it a dangerous tool in the hands of beginners. It may also give your security software an apoplexy, but users skilled enough to use this product will understand that this is not a concern.
Hexplorer has some unique features which make it a powerful editor for images. If you want to open images in a hex editor you should try this out. However, I was unable to increase the font size which made reading difficult.
There are a few more hex editors like frhed, hex editor neo, etc. which I will review shortly. Stay tuned in for updates.