Hi, Allen.
OEM means "Original Equipment Manufacturer". This can mean one of the Big
Boys like HP or Dell, or a "System Builder" like your friendly local Mom &
Pop computer shop. The Big Boys buy in quantity at steep discounts from
Microsoft and revise Windows - sometimes extensively - for compatibility
with their own hardware, plus any other hardware or software they might
include in the "bundle" as they deliver it for retail sale. Mom & Pop will
buy the System Builder version in smaller quantities at wholesale prices;
they might customize the operating system, but they usually don't.
In either case, the lower price comes at a cost: the OEM assumes all
obligation to support the Windows they sell. So, if your Dell printer
doesn't work with your Dell-branded Windows, call Dell, not Microsoft. If
the computer you got from M&P with OEM Win7 pre-installed doesn't work with
the printer you got from M&P - or elsewhere - complain to M&P, not
Microsoft.
The System Builder version of OEM Windows is SUPPOSED to be sold only with a
computer, or with a significant part such as a CPU or hard disk drive. Over
the years, that got stretched to the point that M&P might sell a copy with
just a disk cable; my understanding is that the "with hardware" requirement
is no longer enforced. But the OEM is still obligated to support that copy
of Windows - and the OEM is YOU, the buyer/installer. Again, don't call
Microsoft for support.
That OEM copy of Windows, whether the branded version or the System Builder
version, is forever licensed to THAT computer and cannot be installed and
activated on any other. If that computer is stolen, sold or junked, the
license is gone, too.
A retail copy of Windows - any consumer version, whether upgrade package or
"full" version - comes with Microsoft support, of course. That copy of
Windows can be re-installed on the same computer an unlimited number of
times. And it can be installed on an unlimited number of computers - so
long as it is removed from every other computer first.
But don't rely on some guy in a newsgroup - like me - when it is so easy to
get the official word:
http://windows.microsoft.com/en-US/windows7/products/home
RC