Debug: u (unassemble)

Disassembles bytes and displays their corresponding source statements, including addresses and byte values. The disassembled code looks like a listing for an assembled file. Used without parameters, u disassembles 20h bytes (the default number), beginning at the first address after the address displayed by the previous u subcommand.


u [range]


range : Specifies the starting and ending addresses, or the starting address and length, of the code you want to disassemble.

?: Displays a list of debug subcommands.


Windows XP does not use this command. It is accepted only for compatibility with MS-DOS files. 

Specifying valid range entries

Use range with a debug subcommand to specify a range of memory. You can choose one of the following formats for range: a starting address and an ending address, or a starting address and the length (denoted by l) of the range. For example, both of the following syntaxes specify a 16-byte range beginning at CS:100:

cs:100 10f

cs:100 l 10

For information about assembling mnemonics by using the a (assemble) subcommand, see Related Topics.

For information about displaying the contents of a portion of memory by using the d (dump) subcommand, see Related Topics.


To disassemble 16 (10h) bytes, beginning at address 04BA:0100, type:


Debug.exe displays the results in the following format:

04BA:0100 206472 AND [SI+72],AH 
04BA:0103 69 DB 69 
04BA:0104 7665 JBE 016B 
04BA:0106 207370 AND [BP+DI+70],DH 
04BA:0109 65 DB 65 
04BA:010A 63 DB 63 
04BA:010B 69 DB 69 
04BA:010C 66 DB 66 
04BA:010D 69 DB 69 
04BA:010E 63 DB 63 
04BA:010F 61 DB 61 

To display only the information for the specific addresses 04BA:0100 through 04BA:0108, type:

u04ba:0100 0108

Debug.exe displays the following:

04BA:0100 206472 AND [SI+72],AH 
04BA:0103 69 DB 69 
04BA:0104 7665 JBE 016B 
04BA:0106 207370 AND [BP+DI+70],DH 

Formatting legend



Information that the user must supply


Elements that the user must type exactly as shown

Ellipsis (...)

Parameter that can be repeated several times in a command line

Between brackets ([])

Optional items

Between braces ({}); choices separated by pipe (|). Example: {even|odd}

Set of choices from which the user must choose only one

Courier font

Code or program output

Debug subcommands


Debug: a (assemble)

Command-line reference A-Z

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