PlayStation Architecture

The system includes a 512 KB ROM that stores a Basic Input/Output System (BIOS). This program performs many services, including taking care of the startup process, displaying the user shell, and exposing a collection of I/O routines .

BIOS/Kernel

The BIOS is a critical dependency for games. Not only does this program bootstrap them from the CD drive, it also acts as an intermediary to interact with the console's hardware. This methodology resembles IBM's implementation of their IBM PC BIOS, which encouraged developers to use a standard interrupt table (containing I/O routines) instead of relying on platform-dependent I/O ports.

Having said that, the PS1 BIOS exposes routines such as:

• Commands for the CD-ROM drive.
• Filesystem operations for the CD-ROM and Memory Card.
• Multithreading.
• Standard C functions (e.g. string manipulation and memory operations).

Since access to the BIOS ROM is very slow (as it's connected via an 8-bit data bus), the APIs are packaged in the form of a Kernel and copied to main RAM during boot. Thus, 64 KB of main RAM are reserved for the Kernel, also referred to as PlayStation OS.

Boot process

The CPU's reset vector is located at 0xBFC00000, which points to the BIOS ROM.

Famous splash scene after powering on the console.

PlayStation logo showing after a genuine game is inserted.

The shell is displayed if there isn't any disc inserted.

Similar to the Saturn's boot process, once powered on, the PS1 will:

1. Look for the BIOS ROM and execute routines to initialise the hardware.
2. Load PlayStation OS.
3. Display the splash screen.
4. If there is a CD inserted, the CD-ROM controller will check if it's genuine:
   • It is: The controller will allow to read its contents. In turn, the CPU will look for a file named SYSTEM.CNF (which specifies the location of the executable and some metadata), and continue execution from there.
   • It's not -> The CPU will display an error message.
5. With no CD inserted, the CPU will display the shell.
6. The user is now in control.

The shell is a simple graphical interface that allows the user to copy or delete saves from the memory card; or play an audio CD.