How are MIDIs created?

Are they created when someone records a song/effect etc? I've heard they can't be converted, so is that a popular save style? Will average recording software have an option to save as MIDI?
Thanks;)

midi is not a "recorded" format. think about it like sheet music. It just lists a bunch of notes with pitches, durations, volume, etc. without any recorded data at all (the instrument sounds are stored on your computer completely separate from midi files, so you'll find that people with different sound cards and instrument sets can have completely different sounding instruments). no, you're not going to find "recording" software that saves to midi (assuming you are refering to recording IE with a microphone or via line-in). there are various programs which attempt to take wav files and tries to analyze them and make midis (think about it like transcribing a song you hear on a CD to sheet music), but all of that software tends to have pretty poor results when you have more than one instrument. The way you create midi's are either with your mouse on a keyboard (usually with a sheet music or piano roll display), or you can use a midi instrument IE a midi piano which streams midi data as you play notes. some of the better midi sequencers are Cubase, Cakewalk, and DirectMusic Producer (though DirectMusic outputs to proprietary formats).

EDIT: also, this is better off in another forum, not C++

MIDI is used because it is very efficient. It doesn't take much processor power or databus bandwidth, since you are essentially only sending a little set-up information and musical notes to the sound card. This makes MIDI ideal for games where you want to utilize most of the processing power for the graphics.

When you play a wave file or an mp3, you are sending thousands of samples per second thru the data bus. MP3 files have to be decoded. So, they require processing by the CPU. The down-side of MIDI is that it will sound different on different sound cards, and you can't generate realistic vocals.

Although you can't convert a wave or mp3 to MIDI, you can go the other way and record MIDI output to a wave or mp3.

Here's a site with lots of MIDI info.