How Dreamcast Works

By: Jeff Tyson
Sega Dreamcast hit the market in 1999 and was hailed as an innovative video game system. See more video game system pictures.

With good reason, Popular Science magazine recognized the Sega Dreamcast as one of the most important and innovative products of 1999. Impressive technical specifications, great games and an imaginative advertising campaign heralded the arrival of the latest system from a company known for groundbreaking video game systems

In this edition of HowStuffWorks, you will learn about this phenomenal system, the revolutionary controller that it uses and the proprietary optical storage method chosen by Sega. You will also learn about the VMS, a versatile option that can be used all by itself!


Dreamcast History

Dreamcast was the first video game system to have a built-in modem and 128-bit graphics.

An established leader in the arcade, Sega entered the home market right on the heels of Nintendo. Renamed the Sega Master System, the system known as the Mark III in Japan debuted in the United States in 1986. The Sega Master System used an 8-bit CPU, 128K ROM-based operating system and had a 128K of RAM. Games came on two types of cartridges: a large cartridge that could hold a megabit of game code, and a smaller cartridge that held 256 kilobits of game code.

In 1989, Sega introduced the world's first 16-bit home video game system, the Genesis. Based on Motorola's 68000 processor, the system was technically superior to anything else on the market. But the sheer dominance of Nintendo overshadowed the Genesis, when the rival company debuted the Super Nintendo Entertainment System later that same year.


But Sega beat Sony and Nintendo to the punch with a 32-bit system. The Saturn was officially launched on May 11, 1995. Not only was it the first 32-bit system, but it had two 28.8 MHz 32-bit Hitachi SH-2 processors working in parallel! Sega's Saturn was an amazing system with an incredible architecture, but quickly fell behind the other 32-bit system released that year, Sony's PlayStation.

Code-named Katana, the Dreamcast was released in the fall of 1999, the first system to provide a built-in modem and 128-bit graphics.


Dreamcast Console

Lets take a look at the components inside a Dreamcast, and what their capabilities are:

Processor: 64-bit Hitachi SH-4

Processor: 64-bit Hitachi SH-4


  • Processor clock speed: 200 MHz
  • MIPS (Million Instructions Per Second): 360
  • Bus speed: 800 MB per second
  • Cache: Instruction: 8 K; Data: 16 K

Graphics: 128-bit 100 MHz NEC PowerVR 2DC

  • Resolution: 640x480 or 320x240 interlaced
  • Colors: 24-bit (16,777,216) maximum, as well as 16-bit (65,536) mode
  • Polygon rendering: 3,000,000 polygons per second
  • Memory: 8 MB video RAM

Geometry engine:

  • Alpha blending
  • Perspective correction
  • Gouraud shading
  • Anistropic, bilinear and trilinear mip mapping
  • Z-buffer

Audio: 45 MHz Yamaha Super Intelligent sound processor

  • Channels: 64
  • Sample rate: 44.1 KHz
  • Special effects: reverb, delay and surround sound
  • Memory: 2 MB RAM

Memory: 16 MB

Operating system: Windows CE-based or custom Sega OS

Game medium: Proprietary GD-ROM (Gigabyte Disc)

  • Transfer speed: 1800 kilobytes per second
  • Storage capacity: 1.2 gigabytes
  • Memory buffer: 128 K

Modem: 56 kilobits per second (Kbps)

The Dreamcast is the first console that has a built-in 56 Kbps modem. It was added to enable online play over a phone line, allowing users to play games against each other across long distances. In addition to the built-in modem, Sega is working on a cable or DSL external modem. Broadband networks are being developed that will take advantage of such a modem and enable fast online games for the Dreamcast.


Dreamcast Processor

Inside a Dreamcast console is the RISC processor, similar to that in other video game systems.

Like the N64 and the PlayStation, the CPU in the Dreamcast is a RISC processor. RISC stands for reduced instruction set computer, and means that the instructions and computations performed by the processor are simpler and fewer. Also, RISC chips are superscalar -- they can perform multiple instructions simultaneously. This combination of capabilities, performing more instructions simultaneously and completing each instruction faster because it is simpler, allows the CPU to perform better than many chips with a much faster clock speed.

To lower production costs, the graphics processor is combined with circuitry to control the system through a single application specific integrated circuit (ASIC). Simply put, this means that a custom chip is created to manage all of the necessary components that would normally be handled by separate chips. The Dreamcast sound processor is another ASIC; it combines a 45 MHz ARM7 CPU and a Yamaha digital signal processor (DSP). The ARM7 is a 32-bit RISC chip that handles all processing of the compressed adaptive differential pulse code modulation (ADPCM) audio information in real time. ADPCM is used to sample analog information, compress it at a ratio of 4:1 and store it in digital format.


The Dreamcast has several hardware effects that are handled by the PowerVR chip. They include alpha blending, perspective correction and mip mapping.

Alpha blending uses the alpha channel to add transparency effects to an object. This is a special graphics mode used by digital video, animation and video games to achieve certain looks. Essentially, 24 bits are used to define the red, green and blue amounts, 8 bits each, needed to create a specific color. Another 8 bits are used to create a gray-scale mask that acts as a separate layer for representing levels of object transparency. How transparent an object will be is determined by how dark the gray in the alpha channel is. By making an area of the mask dark gray, you can make an object appear to be very transparent; by making it light gray, you can create special fog or water effects.

Mip mapping is a cool process. It is a form of texture mapping in which different sizes of each texture map are made. In essence, the processor replaces the appearance of an object with a more detailed image as you move closer to the object in the game. Let's take a look at how Dreamcast uses these maps in trilinear mip mapping:

  1. The system calculates the distance from your viewpoint to an object in the game.
  2. The system loads the texture maps for the object. Our three maps will be 64x64 (large), 32x32 (medium), and 8x8 (small).
  3. The system determines the exact size that the image map needs to be. Let's say 16x16 for our example here.
  4. Based on the size, it decides which two texture maps to use. For our example, it will choose the medium and small texture maps.
  5. It will then interpolate (average) between the two texture maps, creating a custom texture map that is 16x16, which it then applies it to the object.

When a game is put in the console, the following happens:

  • You turn the power on.
  • The disc spins up to speed.
  • While the disc is spinning up, the console loads portions of the operating system from ROM into RAM.
  • The game initialization sequence is loaded into RAM.
  • You interact with the game via the controller.
  • As each specific part of the game is requested, the application code and hardware-render geometry are loaded into RAM, while the video and audio portions are usually streamed directly from the CD.
  • The PowerVR chip coordinates everything. In addition to processing graphics, it receives the input from the controller, pulls the data from RAM, sends it to the CPU and directs the use of the audio processor.
  • You are finally beaten by the game and turn it off.

The Dreamcast is the first console that has a built-in 56 Kbps modem. It was added to enable online play over a phone line, allowing users to play games against each other across long distances. In addition to the built-in modem, Sega is working on a cable or DSL external modem. Broadband networks are being developed that will take advantage of such a modem and enable fast online games for the Dreamcast.


Dreamcast Controller

Inside a Dreamcast controller

As it is with other systems, the controller is the primary user interface for the Dreamcast. The standard Dreamcast controller has 11 buttons plus an analog joystick. The buttons include:

  • four buttons arranged as a directional pad on the top left
  • Start button in the top middle
  • four action buttons on the top right
  • one analog trigger on the front left
  • one analog trigger on the front right
  • analog joystick on the top left

Although each button can be configured to perform a specific and distinctive action, all of the buttons, except for the two analog triggers and joystick, work on the same principle. In essence, each button is a switch that completes a circuit whenever it is pressed. A small metal disk beneath the button is pushed into contact with two strips of conductive material on the circuit board inside the controller. While the metal disk is in contact, it conducts electricity between the two strips. The controller senses that the circuit is closed and sends that data to the Dreamcast. The CPU compares that data with the instructions in the game software for that button, and triggers the appropriate response. There is also a metal disk under each arm of the directional pad. If you're playing a game in which pushing down on the directional pad causes the character to crouch, a similar string of connections is made from the time you push down on the pad to when the character crouches.


The analog joystick and triggers work in a completely different way from the buttons described above. The triggers each have a tiny magnet attached to the end of the trigger arm. When the trigger is depressed, the magnet is pushed toward a sensor mounted on the controller's circuit board. Through the process of induction, the magnet creates resistance to the current passing through the sensor. On the bottom of the magnet is a layer of foam padding. Pushing harder on the trigger compresses the padding, which brings the magnet closer to the sensor. The closer the magnet is to the sensor, the more resistance is induced. This variable resistance makes the triggers pressure-sensitive!

The joystick also uses a magnet, along with four small sensors. The sensors are arranged like a compass, with one at each of the cardinal points (north, south, east, west). The base of the joystick is shaped like a ball, with tiny spokes radiating out. The ball sits in a socket above the sensors. Spikes on the socket fit between the spokes on the ball. This allows for an extraordinary amount of movement without letting the joystick twist out of alignment with the sensors. As the joystick is moved, the magnet in the base moves closer to one or two of the sensors, and farther from the others. The system monitors the changes in induction caused by the magnet's movement to calculate the position of the joystick.

The controller has two expansion ports where memory cards, tremor packs, Visual Memory System (VMS) devices and other system additions can be inserted.

A popular option is the tremor pack, which provides force feedback. This feature provides a tactile stimulation to certain actions in a game. For example, in a racing game, you might feel a jarring vibration as your car slams into the wall. Force feedback is actually accomplished through the use of a very common device, a simple electric motor. The shaft of the motor holds an unbalanced weight. When power is supplied to the motor, it spins the weight. Because the weight is unbalanced, the motor tries to wobble. But since the motor is securely mounted inside the tremor pack, the wobble translates into a shuddering vibration of the controller itself.

While standard memory cards can be used with the Dreamcast, the VMS units are unique to this console. The VMS is actually a tiny Personal Digital Assistant (PDA) that fits into the upper expansion port of the controller.

About the size of a business card, each VMS unit contains:

  • 8-bit Hitachi CPU
  • 128 K memory (Flash RAM)
  • Monochrome LCD panel, 48 pixels wide by 32 pixels high
  • Two button (watch) batteries, with auto-off function, to provide power
  • One-channel sound

When the VMS is inserted into a Dreamcast controller, its LCD can be used to perform some unique functions. For example, in a football game, you can select plays without your opponent seeing what they are. In addition to serving as a memory card for the Dreamcast, the VMS can be used as a stand alone device. Small games, as well as traditional PDA functions like a calendar and phone directory, can be downloaded to the VMS and taken with you.


Dreamcast Games

The Dreamcast has a drive similar to other CD-ROM drives, but the optical disc is proprietary.

While Dreamcast games are similar to CD-ROM, the actual optical disc used is proprietary, and can hold up to 1.2 gigabytes of information. This is a lot of space -- most games use only a fraction of it for the actual game. What can eat up the space are the incredible full motion video intros and intermissions included in most Dreamcast games.

There is a noticeable delay while the game is loaded from the CD, which you do not get with cartridge-based games. Of course, the trade-off for faster loading is a significantly smaller amount of storage on a cartridge. Most Dreamcast games use a customized version of Microsoft Windows CE as their operating system; but some use Sega's proprietary Dreamcast operating system.


Dreamcast CDs are just as susceptible to scratches and intense heat as normal CDs. Even more so in fact, since a scratch on a game CD can make it totally unusable.

The games available for the Dreamcast cover all the categories, and its library of games is increasing rapidly. Game prices range from under $20 for certain preplayed titles to over $75 for some of the hottest new games.