Opening files
0FH function is used to open an FCB file the 21H interruption. The element, the name and extension of the file must be initialized previous to opening it. The DX register must recognize the block. If the value of FFH is returned on the AH register when describing on the interruption then the file was not found, if everything came out fine a value of 0 will be returned. If the file is opened then DOS starts the current block to 0, the size of the register to 128 bytes and the size of the similar and its date are crammed with the information found in the directory.