The Arcadia/Starpath Supercharger for the Atari 2600 was a very peculiar device from the second generation of video games. It was a very large cartridge that plugged into the 2600's cartridge port. It contained 6K of S-RAM for loading games off cassette tapes and 2K of ROM for the loading code. The Supercharger was packaged with the game Phaser Patrol. The initial cost of acquiring the Supercharger was higher ($44.95) than a standard 2600 cartridge ($29.95 for many new titles), but the games themselves were often priced lower than cartridge games ($14.95-17.95) due to the use of cassettes, which were much cheaper to mass produce than cartridges. Not included in that price was the cost of the cassette recorder, which the player had to supply. The cassette recorder's line out would be connected via the Supercharger's audio cable.
Ten games were widely available during the accessory's life, two could be purchased by mail order, and four prototypes are known to exist. Among the Supercharger's best games were Dragonstomper, one of the first console RPG games. Communist Mutants from Outer Space is a fun shoot-em-up in the Galaxian vein, and Fireball is a fun Breakout clone. Escape from the Mindmaster uses a very impressive first-person perspective. Even though the library is small, the overall quality of Starpath's 2600 games, in my opinion puts the company in the first rank of 2600 game designers alongside Atari, Activision and Imagic.
I must give special mention to the version of Frogger released for the Supercharger. This version, the so-called Official Release looks, sounds and plays far better than the Parker Bros. cartridge. In fact, it is superior to just about every cartridge release of the game. The arcade original has five lanes of roads and five lanes of water, but many console ports only give you four road lanes. Even more impressive is the fact that the arcade music plays throughout as it should despite the rather humble audio capabilities of the 2600. Many ports cut the theme short and leave you with silence during most of the gameplay. The SNES version is particularly atrocious in this regard because it has no music at all!
When the Supercharger was inserted into the 2600 console, the screen would show "REWIND TAPE PRESS PLAY". Once the player did that, the game would proceed to load, with colored bars on the screen closing in informing the player of the progress of the load. When done, the screen would display "STOP TAPE" for a moment, then the title screen of the game would appear and the player could start playing.
Most games were fully loaded within one load of the cassette, but four games (Dragonstomper, Party Mix, Survival Island, Sweat! - The Decathalon Game) used three loads and one (Escape from the Mindmaster) used four. The tape would be rewound to the beginning, then the first load would start the game, requiring the player to stop the tape. When the game needed the next load, the player would have to start the tape again. If he waited too long in stopping the tape, he would have to rewind it and play it until the game found the beginning of the right load. A load may take approximately 20-40 seconds, depending on the game and which side of the tape was being used. Side A was the fast-load side, Side B was a slower load if Side A did not work with the player's cassette recorder.
The Supercharger digitized the binary data of a game onto an audio cassette. A "0" bit would be an audio wave pulse of 158ms and a "1" bit would take 317ms (fastest speeds) or 900ms/2450ms (slowest speeds). The controller chip in the Supercharger would use an ADC to convert the audio into binary data for the RAM. The Supercharger supports three banks of 2KB of RAM and one bank for the 2KB ROM.
People talking about the Supercharger often state that it increased the RAM capacity of the 2600 (128 bytes) 49-fold. This is not really an apt comparison. An average cart uses a 4KB ROM chip to store program code, graphics and sound. That data must be stored in the Supercharger RAM. A Supercharger game is really like a 6KB cart (with a single load game, otherwise 18KB/24KB cart). However, any portion of that 6KB can be used as extra RAM. Each load of a Supercharger game transforms into an 8448 byte binary file, but that file includes a good deal of space not used by the game (including the space occupied by the ROM bank and a header). Additionally, all ten of the officially released Supercharger games include a "demo" load at the end of the last game load on the tape to show previews of other games. For multiload games, a combined binary file is used with emulators and cartridges like the Harmony Cartridge.
Comparatively, 8KB, 12KB, 16KB and even a 32KB cart were released during the 2600's lifetime. The three 12KB carts from CBS came with 256 extra bytes of RAM, and sixteen of the 8KB, 16KB and 32KB carts from Atari came with 128 bytes of RAM. One game from M-Network, Burgertime, used 12KB of ROM and 2KB of RAM.
The Supercharger was not the only 2600 peripheral that could utilize cassette storage. The CommaVid Magicard programming cartridge came with 2KB of ROM and 1KB of RAM. There were instructions in the manual to modify the cartridge to add support for saving and loading programs to cassette. The Spectravideo Computmate came with 16KB of ROM and 2KB of RAM. The Compumate turned your 2600 into a cheap computer as it came with a 42 key membrane keyboard that would fit on the front grill of a pre 2600jr. machine. It supported saving and loading programs from cassette using a standard cassette recorder. But the impact of these devices pales in comparison to the Supercharger and its games.