HxD is an excellent hex editor that allows you to edit binary code. It is portable, fast, convenient, and has many useful features, such as checksum generation, binary file comparison, support for different encodings, and code templates.
HxD can also edit not only the disk but also the RAM. This makes it a dangerous toy for beginners and a powerful tool for professionals who often work with binary code.
As you know, any file stored on a computer hard disk is a sequence of machine words - bytes. A byte, in turn, consists of 8 bits, each of which can take a value of "0" or "1" This means that a byte can take on 2 8 =256 values between 0 and 255. The number 256 10 written in hexadecimal is a round 3-digit number, 100 16 , which means that not more than 2 bits are needed to represent any number in the range 0-255. This means that the value of each byte is very convenient to write a two-digit number in hexadecimal notation. The hex-editor shows us the file as it is seen by the machine, which is a string of bytes. For example, opening a file with the editor, we see a matrix consisting of 16 columns and a number of lines which depends on the size of the file. Each value of the matrix corresponds to one byte written as a two-digit hexadecimal number. By changing the value of the byte you want, you can change the file itself accordingly.