To create a 100MB partition and mount it on /data, follow these steps: 1. Use `fdisk /dev/hda` (or relevant device) to create a new partition. 2. Type 'n' to create a new partition. 3. Select 'l' for a logical partition if needed. 4. Accept the default starting cylinder by pressing Enter. 5. Specify the size as +100M. 6. Press 'p' to verify the partition list and note the new partition name (e.g., /dev/hda1). 7. Press 'w' to write the partition table. 8. Reboot or run `partprobe` to re-read the partition table. 9. Create a filesystem with `mkfs -t ext3 /dev/hda1`. 10. Create a mount point with `mkdir /data`. 11. Add the new partition to /etc/fstab: `/dev/hda1 /data ext3 defaults 1 2`. 12. Mount the new partition with `mount /dev/hda1 /data`.