The CP/M BIOS (Basic Input/Output System) is the fundamental layer that connects the core CP/M operating system to the specific hardware of a computer.
As defined by the reference, the BIOS is the machine-dependent part of CP/M. This critical component handles all the low-level interactions with the computer's hardware, such as reading from and writing to disk drives, sending characters to the console (screen and keyboard), and interacting with peripherals like printers.
Role and Function of the CP/M BIOS
The primary role of the CP/M BIOS is to provide a standardized interface between the upper layers of the CP/M operating system (like the BDOS, or Basic Disk Operating System) and the diverse hardware found in early microcomputers.
Think of it this way:
- Hardware Abstraction: The BIOS acts as an abstraction layer. The main part of CP/M doesn't need to know the specific technical details of a particular floppy disk controller or terminal hardware. It simply calls standard functions provided by the BIOS (e.g., "read sector," "output character").
- Enabling Portability: This abstraction is key to CP/M's design philosophy. According to the reference, "In theory, all you need to do is change the BIOS and CP/M will work on a different machine." While not always perfectly straightforward in practice, this was the intended mechanism for porting CP/M to various computer architectures built around processors like the Intel 8080, 8085, or Zilog Z80.
Practical Insight
For a manufacturer building a new microcomputer in the CP/M era, the task of getting CP/M to run on their machine largely boiled down to writing the custom BIOS code. This code had to translate the standard BIOS function calls into the specific commands and addresses required by their particular hardware setup. This was often complex and involved detailed knowledge of the machine's input/output ports and controllers.
In essence, the BIOS contained the drivers for the system's hardware, tailored precisely for that machine.
Summary Table:
| Feature | Description | Significance |
|---|---|---|
| Definition | Machine-dependent part of CP/M | Links OS core to hardware. |
| Primary Role | Hardware interface / Abstraction Layer | Hides hardware specifics from the OS core. |
| Key Benefit | Enables Portability (via customization) | Allowed CP/M to run on many different computers. |
The CP/M BIOS was a foundational element that contributed significantly to the operating system's success by making it adaptable to a wide range of early microcomputer hardware configurations.
