DOS
A disk operating system (DOS) will load from a floppy disk each time a computer starts, and will access that disk for software to complete operations. MS-DOS is probably the most well-known DOS, and was purchased by Microsoft Corporation from a system known as QDOS. As operating systems became more complicated and took up more space, they began to be permanently installed on hard drives, which are faster and more reliable than floppy disks, and can store more data. This was encouraged by a steady drop in hard drive prices.