Your Internet connection is only capable of downloading a certain amount of data at one time. This capability is expressed as the connection's bandwidth: an Internet connection with a 10 Mbps download rate can, in theory, download 10 megabits of data per second -- although, in practice, this rate is usually much lower. If you're downloading many songs at the same time, you may not have enough Internet bandwidth left over to perform other tasks. Web browsing, for example, might slow down significantly.
Although audio compression standards such as MP3 and AAC greatly reduce the amount of disk space needed to store a song, a large music collection can take up significant space on your hard drive. Windows uses empty space on your hard drive to store information that it uses to keep the operating system running smoothly; if the hard drive is too full, there may not be enough free space for Windows to function properly. This can slow down the speed of your entire computer system.
Although audio files themselves cannot contain viruses or other malware, downloading songs from illegal or disreputable websites or networks can expose your computer to malware. Fake audio files on peer-to-peer file-sharing networks may in fact be executable malware programs, while shady websites may attempt to install malware on your computer without your knowledge. In addition to other malicious actions, malware programs can take up a large amount of system resources, causing your computer to slow down. Malware can also hijack your Internet connection, reducing your Internet speed.
To avoid using too much bandwidth when you're downloading songs, only download one at a time. If your music collection is taking up too much hard drive space, delete unwanted songs or back up your collection to external media such as a DVD-ROM or an external hard drive. To prevent malware infection, only download music from legal and reputable websites and services. Amazon Music, iTunes and Rhapsody allow you to purchase commercially released songs, and websites like SoundCloud, ReverbNation and Official.fm provide free, legally downloadable music.