If you have the CDs, they have both the Windows and Mac versions of the software. The tax data files can be opened by either version (PC or MAC). So if you need to access a prior year, and if you install the software on your MAC for a particular year, you can open the *.taxYYYY data file fo that year (YYYY=year). If you purchased a download file (Windows version) for a particular year, you'd have to ask Customer Support for the Mac version.
If you are accustomed to using the desktop product, be aware that the Online version has some limitations. It says "Deluxe" by your username above. While desktop Deluxe can handle all the usual forms, Online Deluxe cannot prepare Schedule D,E,F, or C with expenses, and cannot enter a K-1. Online Premier cannot handle Schedule E, F, or C with expenses.
A state return is included with many of the desktop products, but there is an extra fee to prepare a state return in the Online version. In the desktop version, there is a 24.99 state efile fee, but no efile fee for New York state, and no fee to print and mail the state returns.
The desktop version has Forms Mode for viewing/editing on the actual forms when necessary. The Online version does not have Forms Mode.
Printing and archiving is easier with the desktop version. Once you start using Online TurboTax, unless you download the returns and tax data file each year to archive yourself, it's possible to lose access to your returns if you don't keep using a paid product each year (PLUS or higher.)
