Debug: f (fill)

Fills addresses in the specified memory area with values you specify.


f range list


range : Required. Specifies the starting and ending addresses, or the starting address and length, of the memory area you want to fill.

list : Required. Specifies the data you want to enter.

?: 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

Specifying data

You can specify data in either hexadecimal or ASCII format. Any data you previously stored at the specified address is lost.

Using list 

List can consist of hexadecimal numbers or a string enclosed in quotation marks (that is, "string").


To fill memory locations 04BA:100 through 04BA:1FF with five specific values (for example, 42, 45, 52, 54, 41) and repeat the five values until Debug.exe fills all of the 100h bytes, type:

f04ba:100l100 42 45 52 54 41

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


Command-line reference A-Z

© 2017 Microsoft Corporation. All rights reserved. Contact Us |Terms of Use |Trademarks |Privacy & Cookies