Article by Ayman Alheraki on January 11 2026 10:36 AM
In the past, especially during the DOS era, programmers had direct access to all computer components, including memory, input/output units, and graphics cards, without any restrictions. However, with technological advancements, a new operating mode called "Protected Mode" was introduced in modern processors, fundamentally changing how software interacts with hardware.
But why was this protection enforced? What are its benefits? And why is direct hardware access no longer allowed, except through dedicated software such as drivers? This article will explore these questions in detail.
Protected Mode is an operating mode in modern processors (starting from the Intel 80286 and later) that provides advanced features such as memory protection, multitasking, process isolation, and controlled hardware access. This mode differs from Real Mode, which was used in 8086/8088 processors, where software had unrestricted access to hardware.
In older operating systems like DOS, any program could write to any memory location or control any connected device, meaning a simple programming error could lead to a system crash or data loss. In Protected Mode, the operating system manages memory and hardware access, preventing programs from interfering with each other or crashing the entire system.
Unrestricted access to hardware and memory was a major security risk in old systems, as malware could modify system files, spy on users, or even disable devices. With Protected Mode, programs are isolated in dedicated memory spaces and can only access other parts of the system through system calls, which validate each request.
In Real Mode, only one program could run at a time because it directly controlled the hardware. In Protected Mode, multiple programs can run simultaneously, with the operating system ensuring that each program receives its allocated resources without interfering with others.
In Real Mode, programs could access only 1 MB of memory due to the limitations of the 8086 architecture. In Protected Mode, features such as virtual memory and paging were introduced, allowing access to vast memory spaces, even with limited physical RAM.
In modern operating systems like Windows, Linux, and macOS, user programs cannot directly access hardware components such as graphics cards, hard drives, serial ports, or memory. This restriction exists for several reasons:
Instead of allowing every program to control hardware directly, modern systems rely on device drivers, which run with elevated privileges and manage hardware on behalf of other software. This approach creates a secure abstraction layer, preventing programs from misusing hardware or causing conflicts.
If every program could directly control hardware, it would lead to serious conflicts. For example, if two programs attempted to write to a graphics card or hard disk simultaneously, it could result in display errors or data corruption. By requiring software to interact with hardware through the operating system, all operations are properly coordinated.
Allowing software unrestricted hardware access would expose systems to malware and hacking attempts. In Protected Mode, the operating system controls all hardware interactions, making unauthorized actions much more difficult to execute.
In Protected Mode, hardware interaction is handled through intermediate layers, such as:
Device Drivers: These are responsible for direct communication with hardware and are managed by the operating system.
Application Programming Interfaces (APIs): Frameworks like DirectX, OpenGL, and Vulkan provide a secure way for applications to access graphics hardware.
Memory Management Subsystems: The operating system translates program memory requests into physical memory operations.
| Feature | Real Mode | Protected Mode |
|---|---|---|
| Memory Access | Direct, limited to 1 MB | Controlled, supports large memory |
| Security | Weak, full system access | Strong, restricted access |
| System Stability | Prone to crashes | Stable due to process isolation |
| Multitasking | Not supported | Fully supported |
| Hardware Access | Direct | Managed by the OS and drivers |
While direct hardware access was once a feature in the DOS era, it came at the cost of security and stability. As operating systems evolved, it became necessary to protect memory and hardware through "Protected Mode" to ensure a safer and more efficient computing environment.
Even though this shift introduced restrictions for programmers, it was essential to prevent the chaos that occurred in old systems due to software that did not follow proper guidelines.
Have you ever programmed in Real Mode? How do you feel about the impact of Protected Mode on modern programming?