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Bart's free JO.SYS

...Press any key to boot from CD-Rom...

Version 1.4
Last updated on Mar 12, 2002

What is jo.sys? - Introduction - Download - Installation - Limitations - Fix Windows 98 bootsector - Credit - Revision history

 What is jo.sys?

Jo.sys is used to decide if the system should boot from the first harddisk or from the first floppy drive. The default is boot from harddisk, but when a key is pressed within the timeout (default 5 sec.) or when the first harddisk has no valid partitions jo.sys boots from floppy drive. Jo.sys also supports booting from floppy image on a bootable CD-Rom. Very usefull for fully automated installation from floppy boot disks or bootable CD-Roms.

From v1.4 it can also be used to schedule floppy or bootable CD-Rom boots.


Did you notice when booting from a windows 98 CD, a bootmenu "boot from harddrive/boot from CD" is displayed, and you can select the device to boot from. This behaviour is driven by the file "jo.sys", placed in the root directory of the bootable disk.

By looking how the windows 98 jo.sys behaved, I've written my own jo.sys which enables you to boot from harddisk when a 5 second (adjustable) timeout has passed or when the harddisk is not bootable or when you press the "Escape" key. Pressing any other key will boot from the currently booted media, that can be floppy or bootable CD-Rom.

When booting it displays something like:
jo.sys - Screen output
Bart's free jo.sys v1.4
(c) 2000-2002 Bart Lagerweij - http://www.nu2.nu/jo/

Press any key to boot from CD-Rom Drive (Escape to boot from Harddisk)

You now have 5 seconds (default, can be changed using freejo.exe) to hit the spacebar, and boot from floppy/CD-Rom, if not the system will boot from harddisk.


Download jo.sys v1.4 (25KB) (freeware).


You don't install it.

Unzip the files from the download zip file into some directory on your harddisk. Start "freejo.exe" to configure jo.sys behaviour. Then copy the jo.sys file onto a Windows 98 or ME boot diskette and your done.
No need to add anything to your config.sys (like some users seem to think...)


 Fix Windows 98 bootsector

Some Windows 98 bootable diskettes don't work with jo.sys, they have a different bootsector, download w98btfix.zip (16KB) to fix this.
Do no use this fix on Ms-Dos 6.x, jo.sys does not work with Dos 6.x!


Special credit and thanks go out to:

 Revision history

Version 1.4
Version 1.3
Version 1.2
Version 1.1
Version 1.0

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Legal information - [2015-11-29]

Copyright (c) 2000-2015 by Bart Lagerweij. All rights reserved.