The NPD Group today revealed that initial Windows 7 sales were more than twice as strong as for Vista. Although declining to provide the number of copies estimated sold, the researchers note that boxed, retail unit sales of the new OS were 234 percent higher in the first few days than the 2007 release. The jump is credited to both to steep pre-order discounts, strong marketing and similar approaches that helped ship a large number of initial copies.

Simultaneously, though, that same discounting is also understood to have hurt Microsoft's revenue potential. The spike in units didn't translate into as sharp a revenue boost and led to a comparatively modest 82 percent increase in revenue versus what Vista achieved three years prior. Pre-order discounts dropped the average selling price of a Windows 7 Home Premium upgrade from its official $120 price down to $76. Windows 7 Professional's average asking price dropped from $200 to $147, while only the Home Premium Family Pack was left virtually unchanged at $149.

The distinct lack of heavy promotion for Windows 7 Ultimate compared to Vista Ultimate has also damaged Microsoft's maximum growth, NPD says. Compared to the older release, 7 Ultimate has fewer added features and is meant primarily as an equivalent to the Enterprise edition for the home.

Analysts at the group back estimates of a PC sales spike the week of Windows 7's release and say that sales were up 49 percent compared to late October 2008 as well as up 95 percent versus the previous week. However, they caution that Vista's influence was proportionately much higher and saw sales surge 68 percent and 170 percent respectively; absolute PC numbers during launch week actually decreased 6 percent compared to Vista.

The system units also aren't wholly representative of Windows 7 sales as a full fifth of Windows PCs came with XP or Vista during the launch where only 6 percent of PCs during the Vista launch came with a previous version. Netbooks, many of which still come preloaded with Windows XP, are likely to be the cause of the gap.