Atari 2600

The Atari 2600, released in 1977, is the first successful video game console to use plug-in cartridges instead of having one or more games built in. It was originally known as the Atari VCS, for Video Computer System, and the name "Atari 2600" (taken from the unit's Atari part number, CX2600) was first used in 1982, after the release of the more advanced Atari 5200. It was wildly successful, and during the 1980s, "Atari" was a synonym for this model in mainstream media. The 2600 was typically bundled with two joystick controllers, a conjoined pair of paddle controllers, and a cartridge game.

Description

The basic layout of the 2600 is fairly similar to most consoles and home computers of the era. The CPU was the MOS Technology 6507, a cut-down version of the 6502, running at 1.19 MHz in the 2600. The 6507 included fewer memory pins — 13 instead of 16 — and no external interrupts to fit into a smaller 28-pin package. Smaller packaging was, and still is, an important factor in overall system cost, and since memory was very expensive at the time, the 6507's small 8 KB memory space wasn't going to be used up anyway. In fact memory was so expensive they couldn't imagine using up even 4K, and when they got a deal on 24-pin connectors for the cartridge socket, they were only too happy to thereby limit the games to 4K. ¹

Related Topics:
MOS Technology 6507 - MHz - KB

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The console had only 128 bytes of RAM (working storage) that was used by the system to store game state data, i.e. data identifying where the player was in the game, what the score was, etc. RAM was so expensive that there was simply no way to have a "screen buffer", a portion of memory that holds the pattern to be drawn to the screen, at least not with the resolution they wanted. Instead they decided to have enough memory for only one line of the display at a time. When the TV completed drawing that line, the game was expected to quickly stuff the next line into the TIA while the TV was resetting for the next line or just before the beam reached the position of the object that has to be displayed. This is part of the reason that black lines can be seen on the left side of the screen when playing 2600 games.

Related Topics:
Byte - RAM - Resolution

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It was a side-effect of this system, known to 2600 programmers as racing the beam, that made the 2600 one of the most complex machines in the world to program. Nevertheless, it was this same complexity that actually made the system incredibly flexible, and as programmers discovered various "tricks" of the system, games started to do things that were far beyond what the original 2600 designers had ever imagined the system was capable of. Another result of this side-effect made moving objects on the screen no harder to handle for programmers than non-moving backgrounds, which led to many Atari 2600 games having lots of things "going on" on the screen, creating fast-paced action scenes.

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The computers in most homes today are much more powerful than the 2600. The CPU of a typical PC for home use today is clocked at more than 2.8 GHz, or roughly 2,352 times the 1.19 MHz clock rate of the 2600. Also, the 2600's CPU processed 8 bits of data per "clock tick", while modern PC CPUs process 32 or more bits per clock tick. Most computers today have 512 megabytes or more of RAM, which is 4,194,304 times the amount of RAM in the 2600. Atari 2600 games were originally limited to a maximum size of 4 kilobytes, while a CD-ROM, still the most common medium on which modern games are sold, can hold about 650 megabytes, or 162,000 times as much. Also, the Atari had no on board secondary storage, whereas such storage in the form of hard disk drives on today's systems will often have a capacity of 250 GB or more.

Related Topics:
Computers - Today - PC - Clocked - Megabyte - Kilobyte - CD-ROM - Secondary storage - Hard disk - GB

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(¹ The cartridge connector's 24 pins were allocated to one supply voltage line, two ground lines, 8 data lines, and 13 address lines. However, the uppermost address line was used as a so-called chip select for the cartridge's ROM chip, leaving only 12 address lines for the chip's game program. Thus, without special "hardware tricks" built into the cartridge, an Atari 2600 game could occupy a maximum address space of 4K.)

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