There is a list somewhere, here or at dbstalk. The main differences are hard drive size, the newer the bigger, the 23 series doesn't ever need bbcs, and the 20 series has an ota tuner in it.
Yep
HR20 and 21's have 320 GB, Hard drive About 50 HD , 200 SD recording hours
Most all HR20's are silver and have built in OTA. HR 20's are not supposed to be installed anymore for new customers. I don't think HR20 can do 3D either.
HR22 and 23 are basicly twins, Both Black, both have 500 GB hard drives good for 100 HD , 400 SD recording hours. Both will do 3D.
HR 23 doesn't require BBC's
HR 24 has the same Hard drive 500 GB also has a touch front panel instead of buttons, I believe it has a different processor then the others , which makes it faster then the others, but thats debatable.
With Whole home, only 1 remote room can stream from the hard drive at once on the HR 20,21,22,23,and 24.
HR 34 has a 1 TB hard drive (200 HD , 800 SD recording hours) has 5 tuners instead of 2 like the other HR's, same touch panel as HR24. Will Stream 3 remote rooms at the same time. In other words 3 other rooms can watch a recorded program off the HR 34 at the same time with no interuption , all 3 remote rooms can also watch the SAME recording at the same time, and it doesn't have to be mirrored. If room 1 wants to watch the beginning, room 2 can watch the middle, and room 3 can watch the end , and the guy in front of the HR 34 can do what ever he wants. Very neat feature!
Also the HR 34 and 3- H 25's (4 room system) can watch and record live tv in every room all at the same time with no interruption! Don't think that possible with a s
tandard 4 room Hopper setup.
Directv is offering a HR34 and 3 H25's for $99 installed. Plus a number of rebates
Free Premiums for 3 months
Free NFL ST.
Free HD with auto pay
12 month credits of $25 per month and $5 per month.