Good to see this file released, and congratulations to its anonymous author :)

DowngradeFix is indeed suitable for boot2 1.4.1571, which is the earliest boot2 version able to load OS 2.1.0.631 and later.
The newer 3.0.1.99 boot2, packaged alongside OS 3.0.1.1753 and 3.0.2.1791, has received hardening against stack-based buffer overflow exploits...

Why TI didn't want us to downgrade OS? and why should i need to downgrade OS? I read here and there but the goal of the battle between TI and hackers is not explain; just the way to defeat TI but not why...

TI doesn't want us to downgrade because older versions allow native code (C/C++/ASM programming), while 3.0.1 & 3.0.2 don't allow this - yet.
The management at TI keeps being dead set against native code access on the Nspire. They've thrown the Lua bone at the community, maybe they thought it would decrease attempts at bringing native code on the Nspire platform.

Lua is a _very_ welcome development for officially sanctioned programming on the Nspire platform: at long last, there's another choice for high-level programming than the BASIC whose abilities, in some areas, are lower than those of the TI-81 released ~20 years ago.
However, Lua remains a very far cry from native code, in terms of features (no io.* and os.*, etc.), performance (while interpreting Lua is faster than interpreting a number of other languages, LuaJIT can pull 10-100x improvements for some routines - and that's still slower than native code), and expressiveness (access to the internal CAS functions, like on the TI-68k/AMS platform).

Ok, so i understand that they don't want us to use c++ or ASM on the calc, but why? I mean, how could they lose money if i program my calc in C ?? They should be happy that more possibilities useful for eventually more buyers from that new ways to progam the calc???

It's because they are sick people obsessed with controling others.

You're thinking like a member of the open development community, as I do, and as most of the ticalc.org readers do.
But that's not how the top management at TI is thinking :)

AFAWCT from TI's actions, nowadays, the top management cares more about the school system (which, in some countries, is their primary customer), teachers (most of them don't want games) and standardized tests with reduced math functionality (which is a practice completely disconnected from real-world usage...), than about making their calculators useful for usages other than pure high-tech, interactive teaching.
(On a side note, it probably remains to be proved that high-tech calculators make teaching, i.e. transmission of knowledge from teacher to student, more efficient...)

Imagine TI had officially opened access to native code and provided good documentation of the Nspire from the beginning, in 2007. By now, the PTT mode would probably have been completely bypassed, through native code - as it has been for a long time on the 84+(SE).
Not releasing such information, and fighting tinkerers, slows down the progress of tinkerers. It wasn't before 2009 that an entry point was found.
And with official documentation, it would have been immediately clear that the Nspire non-CAS and Nspire CAS hardwares are extremely close to each other, and that TI's ripping money by selling the Nspire "CAS" at a higher price tag than the Nspire "non-CAS" (since both are CAS-capable). This wasn't shown since the end of 2009 - the beginning of 2010.

I forgot to point out that "software costs money" (which I read on the tinspire Google group) is no valid excuse for TI, or resellers, selling the Nspire CAS at a higher price tag than the Nspire non-CAS.
The Nspire CAS is _cheaper_ to produce than the Nspire non-CAS:
* the CAS in the Nspire's OS is extremely similar to that of AMS, the standard TI-68k OS. Deep down, it's the same code base than more than 10 years ago. And stripping it, for the non-CAS mode, _cost_ a little bit of money;
* developing the partial 84+SE emulator in the non-CAS OS cost some money;
* no interchangeable keyboard on the Nspire CAS Clickpad.

If you want a CAS-capable Nspire, without overpaying it, buy a Nspire non-CAS - as simple as that :)

Followup to my previous post.

The fact that they _try_ to lock something down, shows that they're not aware of the history of computing: it consistently shows that locked-down devices eventually get owned. There are more, and more clever, tinkerers than designers.

As sad as it is, due to who Nspire customers are and who dictates the feature set, it makes some business sense for TI to fight calculator enthusiasts and users who want to do more with their calculator than the BASIC whose some abilities, in some areas, trail those of the 20-year-old TI-81, or the recently added but locked-down Lua (which is neither JITed nor on-calc-programmable). Even if they probably overestimate the threat.
The priorities of TI's top management have shifted a lot since TI started providing, a long time ago, relatively open platforms (the TI-Z80 and TI-68k series). At the beginning, ASM was accessible through flaws, but it quickly became official. Perhaps this change resulted from a change of persons in charge ?

You are quite right Lionel "Perhaps this change resulted from a change of persons in charge?" Melendy Lovett is a TI senior vice president and president of Education Technology and if I am not mistaken, she got that job about the time the nspire was being developed.

Melendy Lovett did not come from an engineering or development or marketing or sales background. She is a bean counter and I conclude that because of the way her operation has focused on one set of customers (high school math teachers) to the exclusion of all others (college and university teachers, mathematicians, developers, engineers and scientists), she doesn't understand that business is about relationships. And the damage caused by burning all those relationships isn't over yet. The old customer bases that TI has chosen to ignore, are now actively convincing others not to buy TI calculators and that is going to go on for a long long time. In addition, the high school math teachers whom TI has focused all their effort on can not be to happy that the sets of calculators that they convinced their schools to buy are now made obsolete by the cx models.

Surely TI has handed Casio and Hp the biggest opportunity that they will ever have to take business away from TI. In addition, the million dollar question is why did TI choose to go in a totally new direction and develope a totally new calculator when all they had to do was improve their popular 84, 89, and Voyage calculators in order to continue their business success? From what I can gather, even most high school math teachers seem to prefer the ease of operation of those devices compared to the demands of the much more complicated nspire calculators.