I have six (6) PCs in my very small scientific consulting business. My primary OS is Linux (Ubuntu 14.04 64-bit) and all but one PC (home-built based on Intel i7-4770K processor) are dual-boot Ubuntu 14,04/Windows XP Pro SP3. The XP is for a couple of legacy applications for which there is no satisfactory Linux-based substitute. I understand that what I like need is a fully-licensed copy with support that I can put on my PC and get Microsoft support, if necessary. When I have gone on the Internet looking at pricing, it appears that there are several different version of Win 7 pro on sale. Advice from the experts would be most appreciated.