The only difference between an alien registration card and a green card is the name. The alien registration card (ARC) is the official name given by the United States Citizenship and Immigration Services (USCIS) to signify legal permanent residency, while the name "green card" is a more colloquial and recognizable term used to describe the ARC around the world.
The United States Citizenship and Immigration Services is responsible for approving and issuing all green cards or alien registration cards. Those who qualify for green cards include anyone sponsored by an employer, spouses of U.S. citizens, immediate family members of U.S. citizens and immediate family members of legal permanent residents (in this last case, visas can take up to five years to obtain). To file for a green card, the individual must complete Form I-485 (Application to Register Permanent Residence) and submit it to the USCIS along with the filing fee of $1,010 and any documents required by his case, such as marriage or employment certificates. Once the petition is approved, the applicant receives a registration/green card in the mail.
Green cards are not actually green anymore. The name derived from their former green appearance after the Second World War. The modern card is mostly white with black lettering and contains the holder's photo, name, U.S. address and ID number. It is made out of plastic and is about the size of any other identification card such as a driver's license.
Other names for the alien registration or green card include immigrant visa, permanent resident card and sometimes simply I-485. The name “green card” is used in the U.S. and elsewhere in the world to signify legal alien residency in the U.S.
Once you have a green card, you enjoy the same rights as citizens do. But you can lose an ARC/green card after acquiring it. Committing a felony--even a minor one--could subject you to deportation and the loss of your green card. You will also lose green-card status if you are absent from the country for longer than a year at a time without filing for a reentry pass. Failing to notify the USCIS about a change of address can also cost you your green card, as will helping an illegal immigrant enter the country. A false marriage is also grounds for losing your green card. If you commit a crime while holding a green card, you should consult a criminal lawyer and immigration lawyer.
Possessing a green card for five years qualifies the holder to apply for U.S. citizenship. People whose green cards are based on marriage to a U.S. citizen can apply for citizenship after three years of residency. In both cases, the holder must prove quality of character during the period of residency and have no felonies on their record. No law requires people to apply for citizenship after five years of residency; you can hold the green card for as long as you live in the country, regardless if it is for two years or a lifetime.