ROOMBA "BORN DATE"
Take a look at your serial number, this gives the robot's 'birth date'. Anything made after July 2005 is said to be 2.1 compliant.
Also anything made after October 2005 contains both 2.1 updates and serial command interface (SCI - HACKER : an electronic and software interface that allows you to control or modify Roomba's behavior and remotely monitor its sensors).
Hope this helps you!
You will find the serial number below your Robot's battery as shown here:
and here is how you can tell the date:
You can tell if a Roomba includes the 2.1 updates and SCI code from the outside of the Roomba package by reading the date code on the serial number sticker on the outside of the box.
P.S. : Fourth generation Roomba's have not come out yet. Roomba Discovery series are the third generation vacuuming robot while Scooba is the first generation of floor washing robot.
ROOMBA UPDATES
iRobot started to make the official 2.1 version from late July 2005 onwards and SCI code is included from October 2005 onwards.
iRobot always makes small improvements to their robots, many go un-published, this is why you have certain updates on your robot but not all of them. iRobot continues to do that with their Roombas and Scoobas, learning from customers, returned units and their service center calls and in turn the robots get small improvements. I think iRobot made it formal by calling it 2.1 was due to the accumulated list of improvements was over 20 enhancements to both hardware and software.
It is always good to have the latest and the greatest but doing so you will then get introduced to the rat race of upgrading and never catching on since new small improvements get added even without knowledge.
If you still wish to get the latest then return yours and go to your nearest retailer (Sears, Bed Bath Beyond, Target, Best Buy, Linen & Things...etc) and check out their selections. You can check out their 'born date' from the outside box and decide to purchase the newest.
There are some improvements with v2.1 of Roombas but they are not revolutionary but instead evolutionary updates. It will continue cleaning very much the same way with subtle changes on it's behavior and other minor enhancements as listed here by iRobot (http://irobot.com/sp.cfm?pageid=46&id=199):
"What is Roomba 2.1?
iRobot engineers are constantly working on Roomba to improve the product and Roomba 2.1 is our latest robotic vacuum cleaner.
What makes Roomba 2.1 better?
1. iRobot's new AWARE robotic intelligence provides greater room coverage.
2. A redesigned cleaning system with improved brushes which improves brush contact with floors and gives you better cleaning efficiency.
3. Easier cleaning.
4. Improved robot durability.
5. New brush bearings resist hair build up.
6. New Software that improves Roomba's cleaning efficiency.
7. Improved charge circuitry to provide longer overall battery life.
8. Improved side brush design.
9. Improved balance of the vacuum impeller.
10. Improved vacuum bin contacts.
11. Improved wire routing for system durability.
12. Optimized sensors for system efficiency.
13. Overall 20 enhancements to both hardware and software have been incorporated in Roomba 2.1."
Hope that you find this information useful!
Kind regards,
Nikolai - RoombaReview.com