So it's no surprise that Microsoft includes its Windows Defender antimalware app in Windows 8 and Apple has included antimalware detection in OS X Mountain Lion, with daily checks to update signatures and remove known malware. Windows' registry does make it harder to truly eliminate malware than Apple's approach of relying on discrete files and folders that can simply be deleted if found to be harmful. But there are more tools available to monitor and protect Windows, commensurate to its greater risk.
Both OSes' boot loaders include antimalware detection, and OS X has a password-protected firmware option to prevent startup from external disks; users can't bypass the startup password by opting for their own disk. (One of OS X's handy features is that you can boot a Mac from external disks and network volumes easily, which is great for testing and shared environments.)
Beyond such application security, both OSes support FIPS 140-2 cryptographic encryption (new to Mountain Lion and requiring an additional installation). Both OSes provide on-disk encryption, as well, though Microsoft's BitLocker requires a Trusted Platform Module (TPM) chip to implement it fully, and few PCs have such a chip. Thus, enabling disk encryption is easier in OS X.
Also easier in OS X is data security, thanks to the included Time Machine backup program. With Time Machine, it's dead simple to back up a Mac, and the backups can be encrypted and (new to OS X Mountain Lion) even rotated among multiple disks. System restoration is also exceedingly easy, with no driver installation or command-line setup involved.
Windows 8 does introduce File History, which backs up data files in certain locations to your choice of your startup disk, an external disk, or Microsoft's SkyDrive cloud storage service. Like Time Machine, File History keeps incremental versions of these files so that you can roll back to a previous point in time, but unlike Time Machine, it can't restore your whole PC in case of a crash or simply to transfer your environment to a new machine.
Windows 8: 10
OS X Mountain Lion: 8
Because Windows 8 is Windows 7 with the Metro environment tacked on, it is compatible with all the software, hardware, and services you already have. Yes, some older PCs won't run it, but that's about resource requirements and lack of drivers for those that also don't support Windows 7.
OS X Mountain Lion of course runs only on Apple's Macs, for which there is a smaller set of hardware and software available than for Windows. And Apple is ruthless in dropping technologies over time as it deems them problematic or limiting, such as removing RSS support in its email client and browser in Mountain Lion. The truth is that the everyday hardware people use -- mice, keyboards, storage devices, printers, and displays -- work on Macs, and the same is true for mainstay software such as Microsoft Office and Intuit QuickBooks, though often (as in these two cases) with inferior versions.
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