What are the minimum specifications for Android?
Assuming that the handset and carrier both allow the OS to be upgraded, what is the minimum specification needed for Froyo in terms of processor, screen, and other capabilities?
Almost any Android phone can run Froyo (if you root it and it can run Cyanogen) but carriers won't be upgrading the majority of the phones that were out before the "Droid" era (which was out around November of 2009). Basically, if the phone came with 2.0 or above it'll probably get upgraded to 2.2 (Froyo) but lots of phones that came with 1.5 or 1.6 just arn't powerful enough for all of Froyo (Cyanogen had to disable a few features to get it to work on the first Android phone, the G1).
The Android CDD has the minimum specs. There is no minimum processor, it just has to be "fast enough".
Well, i'd say the G1 specs, since Cyanogen has it running on those, from what i understand it was a bit tight to fit froyo on a G1/Dream but it was possible
Without rooting the phone, the Motorola Droid or N1 is probably the minimum spec for Android 2.2. I don't really see many older phones than the Droid getting 2.2.
With rooting the phone, I would say the G1 with CyanogenMod or similar, but it will not be feature complete as that phone simply cannot support some features, such as LiveWallpapers.
I can confirm that I am running CyanogenMod 6 (Froyo) on a HTC Hero - which is not the highest spec phone on the block in terms of CPU, RAM (and anything else come to think of it)
Performance is greatly improved over the standard HTC spin and has given my phone a new lease of life (so I can buy a new laptop instead of a new phone!)