Q - People talk about a cart's firmware/menu/OS, what are these?
A - The cart's firmware is the software that's installed onto the cart itself (not your MicroSD). This is generally only updated to bypass a new 3/DS/i firmware that attempts to block flash carts. On the other hand, the menu/OS is what you run on your MicroSD that lets you choose and launch ROMs and homebrew. This is sometimes called the "firmware", but in reality it's not, it's the OS (Operating System) of the cart. In general a cart type will have it's own firmware. For example Acekards use AKAIO, the Supercard DSTWO uses EOS, some R4 models can use Wood, and so on and so forth. YSmenu is a special menu/OS that's intended to run on as many carts as it can. Having a cart that gets updates to it's menu/OS is important, as this is what provides fixes for new games, and new features.