PC Boot Loader
A PC Boot Loader game is one released in the early days of PC gaming, back when operating systems were still optional and computers only loaded their BIOS by default. To get these games to work, you would turn off your computer, insert the disk into the drive, and then turn your computer back on. The IBM PC (or compatible) would check the disk, see that the game was there, and run it rather than load all the overhead of a full OS like DOS. While boot loading games existed for several home computer platforms, for the purposes of this Wiki, they refer only to IBM PC compatible games.
The first PC boot loaders were released in 1981, and quickly became the standard format for PC games. By the end of the 1980s they decreased to a scant few as developers began to rely more and more on DOS. By 1990, only a handful of games were still being released as boot loaders. Since the platform is based on the generic ability of a computer to boot from an external device, it will probably never be discontinued, though there is no reason beyond nostalgia to boot from a disk anymore.
Note that a boot loader is different than a boot disk. In the 1980s and 1990s, when DOS had problems allocating memory, it wasn't uncommon for a game to require more memory than DOS had available after loading its various background programs. Boot disks were a way to load DOS with a different, and usually less memory-intensive, configuration so the game would have enough memory to run. By contrast, boot loader games don't load the operating system at all.
Music and Sound
Since this is a software platform, it doesn't have any built-in audio capabilities, but most PC boot loaders assumed the computer they were running on was equipped with a PC Speaker.
Designers developing boot loader games usually had to write their own audio drivers in assembly language. Since the PC Speaker is such a low fidelity audio device, this wasn't too difficult. Audio could be adjusted by frequency, but volume could only be on or off. However, a well-made driver could still do a lot with that. Nevertheless, since computers that still required software to be boot-loaded were not very powerful, there usually wasn't enough disk space or a fast enough CPU to allow for impressive audio.