This forum has a lot of information hidden away in its depths. The repetition of the same questions indicates that locating that information is not as easy as it could be.
Ideally I would like to create a metasearch so you could use one search box- but you would be deluged with possible answers and I don't have the resources anyway. So... I have created a page of searches for you to use.
In some cases you need to prefix your search with "ti-99/4a" in quotes to focus the results on our favourite computer - I have noted this when especially relevant. How you use quotation marks is important in reducing unhelpful results - but overuse may cause you to miss something, so practice with varying search forms. Just putting lots of words without quotation marks is not usually useful and just one or two words may overwhelm you..
So- open this htm file in your browser and save it to your local machine where you can then open it at will.