I don't remember how I created that setup, and I cannot do it again (still trying).I think the Yosemite update would have gone OK if I only had one windows partition.With Mini Tool I was able to create a second windows partition after deleting the Mac recovery partition, because MBR has room for only 4.
However, some users complain that their Mac computers stops working after installing new mac OS Sierra.
In other words, just because your Mac was compatible with El Capitan (OS X 10.11), Yosemite (10.10), Mavericks (10.9), or Mountain Lion (10.8) may not necessarily mean that you'll be able to upgrade to Sierra.
Some Mac models, such as 20 i Macs, are being left behind with El Capitan as their maximum OS version.
Certain older Mac models are still limited to Lion (10.7), which has not been getting security patches since Yosemite was released two years ago.
Some early Intel Macs released in 2006 are stuck with Snow Leopard (10.6), which hasn't received security updates since the release of Mavericks three years ago.
While you should get a great experience from mac OS Sierra, you may encounter the odd issue – which is why we’re here.