Microkernel - Introduction

Introduction

Early operating system kernels were rather small, partly because computer memory was limited. As the capability of computers grew, the number of devices the kernel had to control also grew. Through the early history of Unix, kernels were generally small, even though those kernels contained device drivers and file system managers. When address spaces increased from 16 to 32 bits, kernel design was no longer cramped by the hardware architecture, and kernels began to grow.

The Berkeley Software Distribution (BSD) of Unix began the era of big kernels. In addition to operating a basic system consisting of the CPU, disks and printers, BSD started adding additional file systems, a complete TCP/IP networking system, and a number of "virtual" devices that allowed the existing programs to work invisibly over the network. This growth continued for many years, resulting in kernels with millions of lines of source code. As a result of this growth, kernels were more prone to bugs and became increasingly difficult to maintain.

The microkernel was designed to address the increasing growth of kernels and the difficulties that came with them. In theory, the microkernel design allows for easier management of code due to its division into user space services. This also allows for increased security and stability resulting from the reduced amount of code running in kernel mode. For example, if a networking service crashed due to buffer overflow, only the networking service's memory would be corrupted, leaving the rest of the system still functional.