The Atari 8-bit family is a series of 8-bit home computers introduced by Atari, Inc. in 1979 and manufactured until 1992. All of the machines in the family are technically similar and differ primarily in packaging. They are based on the MOS Technology 6502 CPU running at 1.79 MHz, and were the first home computers designed with custom co-processor chips. This architecture enabled graphics and sound capabilities that were more advanced than contemporary machines at the time of release, and gaming on the platform was a major draw.
The original Atari 400 and 800 models launched with a series of plug-n-play peripherals that used the Atari SIO serial bus system, an early analogue of the modern USB. Over the following decade, the 400 and 800 were replaced by the XL series, then the XE. The XL and XE are much lighter in construction and less expensive to build, while also having Atari BASIC built-in and reducing the number of joystick ports from 4 to 2. The 130XE, released in 1985, increased the memory to 128K of bank-switched RAM.
The Atari 8-bit computer line sold two million units during its major production run between late 1979 and mid-1985. The primary competition in the worldwide market came several years later when the Commodore 64, the first computer to offer similar graphics performance, was introduced in 1982.
You can browse and download most available games for free below, but you will need an emulator also to play them. For Atari 400 / 800 we recommend http://www.virtualdub.org/altirra.html but you can use any emulator of your choice and even original hardware if you have the know how!