Microsoft KB Archive/57627

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Comparing Keyboard Response Time in Different Versions PSS ID Number: Q57627 Article last modified on 02-02-1993 PSS database name: O_MSDOS

3.x 4.00 4.01


The information in this article applies to:
- Microsoft MS-DOS operating system versions 3.x, 4.00, and 4.01


Are there any plans to increase the keyboard buffer size in future versions of MS-DOS? Also, does the keyboard response time vary in different versions of MS-DOS?


Currently, we do not plan to increase the keyboard buffer size in future releases of MS-DOS. However, in OS/2 the keyboard buffer size has been increased to a capacity of 255 characters.

The following is a list of the different types of keyboard buffers in MS-DOS:

Owner Location Character Capacity —– ——– ——————

BIOS 0040:001E 15 characters MS-DOS COMMAND.COM 128 characters USER via INT21 USER SPECIFIED 255 characters

In regard to keyboard response time, any version of MS-DOS is only as fast as the underlying BIOS and hardware. For example, if the BIOS has the additional overhead of processing extended functions/characters for the 101 keyboard, this BIOS might be slightly slower than a BIOS that does not process extended functions.

Listed below is a short program that you can execute from your AUTOEXEC.BAT file to make your keyboard operate at the fastest possible speed. However, you will need an AT BIOS dated 11/15/85 or later, or a PS/2 machine, for the program to work properly. This program sets the repeat rate to a maximum of 30 characters per second, and sets the delay-before-first-repeat rate to a minimum of 250 ms (milliseconds).

Use DEBUG to enter the following program as a .COM program, save the program, and then put the program on your execution path.


mov ax,0305 xor bx,bx int 16 mov ax,4c00 int 21

Additional reference words: 3.20 3.30 3.30a 4.00 4.01 noupd

Copyright Microsoft Corporation 1993.