[MP-Ryan]

I haven't had a need to backup a full disk partition in a while (OK, a decade), but with the impending upgrade of the system I'm going to want to keep one temporarily just in case.  Anyone able to recommend a freeware or open-source tool that can create a backup of my primary partition on the SSD (boot partition)?  It's ~200 GB.

[Bobboau]

clonezilla

[rev_posix]

What bobboau said

[jr2]

http://www.macrium.com/reflectfree.aspx

If you want to be able to image the drive while using it (which is convenient).

Also supports compression, as well as intelligent sector copy (only used sectors are copied), or you can do a bit-for-bit copy if you wish.

[Phantom Hoover]

dd

[Flaser]

For Windows there's ImageX, Microsoft's own backup & deployment tool.
https://technet.microsoft.com/en-us/library/cc722145%28v=ws.10%29.aspx
https://technet.microsoft.com/en-us/library/dd744320%28v=ws.10%29.aspx

It's part of the freely available Windows Automated Installation Kit (WAIK):
https://www.microsoft.com/en-us/download/details.aspx?id=5753

WAIK has been renamed (Windows) Assessment and Deployment Kit (WADK or ADK) for Windows 8/8.1:
https://www.microsoft.com/en-us/download/details.aspx?id=39982

...and they replaced ImageX with another tool called DISM, which pretty much does the same thing (capture/backup/restore/deploy partitions/systems):
http://justworks.ca/blog/goodbye-imagex-hello-dism
https://technet.microsoft.com/en-us/library/hh825236.aspx

...and there's new a version of ADK for Windows 10:
https://msdn.microsoft.com/en-us/windows/hardware/dn913721.aspx

THESE ARE ALL FREEWARE SOFTWARE.

EDIT:

Apparently you don't need to download ADK if all you want is DISM, it's part of Windows 8:
http://mythoughtsonit.com/2013/02/dism-exe-replaces-imagex-exe/