Treat the 2 uses differently.
An external hard drive for Mac and Windows, Backup Plus Ultra Slim offers 2TB of space for photos, music, and more; Enjoy fast plug-and-play connectivity with the included USB 3.0 cable; Back up files with a single click or schedule automatic backups—it works with both Mac and Windows. Reformatting may be required for use with Time Machine. Seagate Backup Plus Slim for Mac Portable Drive - Quick Start Guide, Installation, Troubleshooting Tips & Downloads.
A) you do not need to use any drivers for the disk. You can format the disk for Mac use with the Applications -> Utilities -> Disk Utility.
B) to backup your Mac for the upgrade, format the drive as a Mac OS Extended (Journaled) disk drive. This will NOT be readable by Windows, but you can reformat for that task after you upgrade.
![Backup Backup](https://assets.pcmag.com/media/images/519924-seagate-backup-plus-ultra-slim.jpg?thumb=y&width=980&height=417)
Use a Mac backup utility to copy your Mac's data to the external disk. Disk Utility -> Restore can be used to copy your entire system to the external disk, just specify the external disk as the destination for the Restore.
Or you can use SuperDuper (free for a full clone, you only pay if you want the incremental and scheduling features). I think there are older versions available for 10.5
Or Carbon Copy Cloner (free 1 month fully enabled demo). I think there are older versions available for 10.5
C) After you have performed your upgrade and your data is safe, you can choose to blow away the contents of the external disk and reformat it as a Windows exFAT drive that can be read by both Mac and Windows. NOTE: Some Mac file attributes may not transfer, but that would only matter if you were trying to use the exFAT formatted drive as a Mac backup device. But as a file transfer device or a device for storing documents, pictures, movies (data, not programs), then exFAT is OK for that.
If you want to transfer data to Windows first, then just create the exFAT first, transfer your data, then reformat for Mac backup and upgrade. Mac snipping tool shortcut.
How To Install Seagate Backup Plus
Wd elements not showing up on mac.
How To Use Seagate Backup Plus Slim
![Seagate Backup Plus Slim How To Use With Mac Seagate Backup Plus Slim How To Use With Mac](https://assets.gadgets360cdn.com/shop/assets/products/seagate-backup-plus-slim-external-hard-drive_1580965620.jpeg?downsize=390:*&output-quality=80&output-format=jpg)
Seagate Backup Plus For Mac
NOTE: you should be able to use file sharing between the Mac and the Windows system for transferring files.