Twenty-five years ago, Nintendo launched the Nintendo Entertainment System (lovingly known as the NES) in the United States. The iconic gray-and-black 8-bit console (which sold 61.9 million units worldwide) pushed boundaries in both hardware and software design and served as a rallying point for the suffering video game industry in the post-Atari era.

In honor of this anniversary, let’s take a peek inside the console that first brought Mario, Zelda, and Metroid to life.

This is the NES. On the left we see the main console, which measures roughly 10 inches by 8 inches by 3.5 inches in size. To its right sits the now-iconic control pad, which plugs into the console via one of two black connectors on the right side of the console’s face. The front of the NES also contains two switches (power on/off and reset) and a hinged door that conceals a slot for game cartridges.

The NES was the first game console in the U.S. to ship with discrete composite video and audio-out jacks. We call them AV jacks today, and they’re present on most TVs made after about 1995 or so. In 1985, however, the only consumer equipment with jacks to receive these signals were VCRs and very-high-end TV sets. Most consoles until the mid-1990s sent their audio/video signals to a TV’s antenna jack.

In a rear corner of the NES lies an alcove sheltering some points of interest. From left to right we see the power connector, a channel 3-4 selector switch (for choosing which TV channel the game will display on), and the RF audio/video output that leads to an external RF switch (which, in turn, attaches to an antenna terminal on a TV set).

On the bottom of the NES sits a small plastic cover that, when removed, allows access to an expansion port. The actual connector is obscured by a breakable plastic tab, which reveals how often Nintendo thought you’d use it. Neither Nintendo nor any third-party company sold a product that used the port.

The NES in Japan (known as the Famicom) received accessories like a disk drive, 3D glasses, a modem, and a keyboard/computer kit, so Nintendo likely had those possibilities in mind for the NES.

Now it’s time to take the NES apart. After removing six screws, the top half of the console’s plastic case comes off easily, exposing the guts of the console–which are still screwed into the bottom half of the case at this point.

With the top placed aside, we now concentrate on the bottom half–where all the action is. In this slide, I’ve unscrewed and removed the top half of the console’s metal RF shielding.

RF (radio frequency) shielding is designed to prevent interference between the console’s electronics and the outside world, especially TV sets, which are susceptible to stray electromagnetic emissions that occur from any functioning circuit.

The NES’s unique zero-insertion-force (ZIF) cartridge loading mechanism (seen here in its up and down positions) dictated many elements of the console’s design, including its size and shape. To operate it, one would slide a cartridge into the mechanism from the front and push the cartridge down, locking the cartridge into place before powering on the system. While innovative, this mechanism would also turn out to be the console’s Achilles’ heel (more on that ahead).

I’ve now unscrewed the motherboard/cartridge tray assembly (left) and removed it from the bottom half of the NES case. The console’s power and reset switches (seen here still attached to the NES case) connect to the motherboard via a small bundle of wires, which I have detached from the motherboard in this photo. Likewise with the control pad connectors, which also remain in the case for now.

Here we see the motherboard assembly separated into three pieces: the cartridge loading-tray mechanism, the motherboard itself, and the U-shaped cartridge connector. Let’s zoom in on the U-shaped connector and examine it next.

The cartridge-to-motherboard connector you see here was the NES’s single largest point of failure. Nintendo designed it so a game cartridge could be inserted at an angle with no resistance, then pushed down in the spring-and-latch loading tray inside the NES, bringing the cartridge’s conductive pads in full contact with the connector’s pins. Repeat that action a thousand times, and this connector starts to wear out–as it did in millions of NES consoles around the world.

At left, we see a modified 8-bit 6502 CPU that ran at 1.79MHz. Near the center sits a custom “picture processing unit” (PPU), which generated the console’s video image. Also seen is the never-used expansion port connector (discussed earlier) and a 72-pin connector at the bottom of the board that would eventually lead to a game cartridge. The RF modulator box took data from the PPU and turned it into audio and video output for a TV set.

Now that we’re done with the console, let’s examine two other important NES components. Here we see a Super Mario Bros. “Game Pak” (Nintendo’s fancy name for a software cartridge) sitting behind the iconic and highly influential NES Control Pad. The Control Pad shifted game controller design away from joysticks thanks to its excellent cross-shaped directional pad, which had previously appeared on the Japanese version of the NES in 1983. We’ll take a look inside both components in a moment.

In the Control Pad, all surface controls (except Start and Select) are composed of hard plastic buttons that rest upon springy rubber inserts with conductive pads on them. When a player pushes a button, it collapses the rubber insert, and the conductive pad completes a circuit on the green PC board seen here, registering a button press with the console. The Start and Select buttons work the same, albeit without the extra plastic component on top.

Surprisingly, the actual core of a game cartridge takes up very little room inside its plastic shell. This cartridge’s two ROM chips contain the game software; one stores the actual program code, and the other stores graphics data.

A lockout chip, placed in every licensed cartridge, ensured that the game was authorized by Nintendo. It caused quite a bit of trouble when combined with dirty cartridge connectors, resulting in the “blinkies.” That, however, didn’t stop millions of people from enjoying the NES, which became a potent cultural force for an entire generation.

Want more cool teardowns of classic tech gear? Check out these slideshows:

Gadget Autopsy: The Nintendo Game Boy

Inside the Apple IIc

Inside the Commodore 64