A sound card is an expansion card that fits into the computers PCI slot on the motherboard. Sound cards include an amp and You can easily plug in speakers. The
sound card changes analog to digital and then back to analog. Instead of DACs the sound card uses a codec a codec which performs different tasks. X-Fi which means extreme fidelity. Active modal architecture gives different sound options for games and music. A digital signal processor which has 51 transistors. Multiple processing engines perform different tasks. A 24 bit Crystalliser reverses the sound quality loss in 16bit CD recording. Sound cards use frequency modulation where many different sound waves make complex shapes.
In addition you can plug in a microphone and a controller. Sound cards can be used for a home theatre system , Gaming for better audio and music production. Sound cards take the load of your cpu. I has multiple ports for additional 3.5mm headphone jacks.