What Does the CPU Do on a Classic Arcade PCB?

By HighScoreSaves Technical Team

Reviewed and updated August 23, 2026

Open a classic arcade cabinet and the main game PCB may contain dozens or even hundreds of individual electronic components. One of the most important is the CPU.

The CPU is not the entire arcade game, and it does not independently contain everything required to create the picture, sounds, controls, or game program. Instead, it works with ROM, RAM, video circuitry, sound hardware, input circuitry, and other components on the original PCB.

Understanding the CPU is particularly useful when identifying an original arcade PCB or installing a daughterboard-style upgrade.

What Does CPU Mean?

CPU stands for Central Processing Unit. In simple terms, it is the processor responsible for executing program instructions and performing much of the decision-making required while the game operates.

The game's program code is generally stored in ROM devices. The CPU accesses those instructions and executes them in a defined sequence.

That interaction is one reason it is useful to understand the difference between the processor and the memory devices around it. Our guide to original arcade ROMs explains the role of program, graphics, and sound-related ROM data in more detail.

What Does the CPU Actually Do During a Game?

The exact architecture varies from game to game, but the CPU can participate in tasks such as:

• executing the game's program instructions;
• processing joystick, button, start, and coin inputs;
• tracking player and enemy behavior;
• performing game-rule and collision calculations;
• updating score, lives, timers, and other changing information;
• reading and writing data in RAM;
• communicating with video, sound, and other supporting circuitry; and
• responding to events generated elsewhere in the hardware.

A CPU therefore plays a central role in the game, but it works as part of a larger hardware system rather than operating alone.

CPU vs. ROM: What Is the Difference?

A common source of confusion is the difference between the CPU and the program ROMs.

The CPU executes instructions. The program ROMs store program data that the processor uses.

Replacing or moving a CPU does not automatically replace the original game program. Likewise, a ROM chip does not execute the game by itself.

This distinction is especially important when working with an original-PCB upgrade kit because different components may serve very different purposes even when they are physically located close together.

CPU vs. RAM: What Is the Difference?

RAM provides working memory that can change rapidly while the game is operating. The CPU reads information from RAM, writes new information to RAM, and uses that temporary data while executing the game program.

For example, changing information associated with gameplay may exist in RAM while the cabinet is powered.

Because much of the RAM used in classic arcade hardware is volatile, that information normally disappears when power is removed. See Arcade RAM Explained for a closer look at working memory on original arcade PCBs.

Does Every Classic Arcade Game Use the Same CPU?

No. Classic arcade games were built around many different processors and hardware architectures.

Even games from a similar period can use different CPU families, clock speeds, supporting components, memory maps, and PCB layouts. Some arcade systems also use more than one processor, with separate processors assigned to different portions of the hardware.

That is why the game title alone should never be used to assume CPU or upgrade-kit compatibility.

How Do You Identify the CPU on an Arcade PCB?

A CPU is usually an integrated circuit mounted directly to the PCB or installed in an IC socket. Identification may involve checking:

• the markings printed or molded on the chip;
• the component location on the PCB;
• the original game manual or schematic;
• PCB silkscreen markings;
• known board revisions; and
• the physical package and pin count.

Do not identify a component solely by its size or location. Several integrated circuits on the same PCB can look very similar.

Our original arcade PCB identification guide explains what should be documented before ordering an upgrade.

Why Does the CPU Socket Matter?

Many HighScoreSaves upgrades for supported original arcade PCBs use the existing CPU location as an interface point.

In a typical supported installation, the original CPU is carefully removed from its socket. The daughterboard is installed in the CPU socket, and the original CPU is then installed into the appropriate socket on the daughterboard.

The exact procedure is game-specific, so the installation guide for the particular kit should always be followed.

This also means that the condition of the original CPU socket matters. Weak contacts, corrosion, cracked socket bodies, previous repairs, damaged solder joints, or poor mechanical fit can cause problems even when the upgrade itself is functioning correctly.

Before installation, see How to Inspect an Arcade CPU Socket Before Installing an Upgrade Kit.

Why Is Pin 1 Important on an Arcade CPU?

Integrated circuits have a defined orientation. Pin 1 identifies the starting point for the device's pin numbering and helps establish how the CPU must be positioned in its socket.

A CPU must not be installed based only on the direction of its printed text.

Before removing the processor, document its original orientation. During installation, compare the CPU notch or Pin 1 indicator with the socket, PCB, daughterboard, and game-specific installation instructions.

For more detail, read How to Identify Pin 1 on an Arcade CPU, ROM, Socket, and Daughterboard.

Why Would an Arcade Upgrade Kit Use the Original CPU?

A daughterboard-style upgrade can add functionality while retaining the supported original arcade PCB and processor.

Depending on the particular HighScoreSaves kit, added functionality may include features such as Free Play, persistent high-score storage, settings options, multigame functionality, ROM Saver, or optional Wi-Fi leaderboard support.

The daughterboard is not simply a generic replacement game board placed inside the cabinet. It is designed around specific original arcade hardware.

Our article What Is an Arcade Daughterboard and How Does It Work on an Original PCB? explains this relationship in greater detail.

Can You Damage an Arcade CPU While Removing It?

Yes. Socketed CPUs can have many relatively thin pins. Pulling one end upward too far while the opposite end remains seated can bend pins or place unnecessary stress on the component and socket.

A CPU should be lifted gradually and evenly using an appropriate technique. Never force a processor that does not appear to be moving normally.

See How to Remove and Reinstall a Socketed Arcade CPU Without Bending Pins before attempting removal.

Does a CPU Problem Always Mean the CPU Is Bad?

No. A game that does not boot or behaves incorrectly can have many possible causes.

Problems involving power, sockets, RAM, ROM, address or data circuitry, clock generation, reset circuitry, damaged traces, connectors, previous repairs, and other hardware can sometimes produce symptoms that appear processor-related.

The CPU is one component in a complete system. Troubleshooting should therefore be systematic rather than based on replacing parts solely because a symptom appears to involve the processor.

Why CPU Identification Matters Before Ordering an Upgrade Kit

Original-PCB upgrade compatibility depends on the actual hardware installed in the cabinet.

A cabinet can contain an original PCB, another revision, a conversion, a bootleg board, a reproduction PCB, or a replacement/emulation system. Two cabinets displaying the same game can therefore contain very different electronics.

If your board does not match the expected original hardware, review Will an Arcade Upgrade Kit Work on a Bootleg, Conversion, or Reproduction PCB? before ordering.

Key Takeaway

The CPU is the processor that executes the game program and coordinates much of the changing logic required while a classic arcade game operates. It works together with ROM, RAM, video hardware, sound circuitry, inputs, and other components on the original PCB.

For many supported HighScoreSaves upgrades, the CPU is also important because the original processor is moved to a game-specific daughterboard installed through the original CPU socket. Correct PCB identification, socket condition, Pin 1 orientation, and careful CPU handling are therefore essential parts of a successful installation.

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Classic Arcade • Modern Features