Linux kernel and classic Unix systems

 Main differences exist between the Linux kernel and classic Unix systems:

1.Linux supports the dynamic loading of kernel modules.Although the Linux kernel is monolithic, it can dynamically load and unload kernel code on demand.

2.Linux has symmetrical multiprocessor (SMP) support.Although most commercial variants of Unix now support SMP, most traditional Unix implementations did not.

3.The Linux kernel is preemptive. Unlike traditional Unix variants, the Linux kernel can preempt a task even as it executes in the kernel. Of the other commercial Unix implementations, Solaris and IRIX have preemptive kernels, but most Unix kernels are not preemptive.

4. Linux takes an interesting approach to thread support: It does not differentiate between threads and normal processes.To the kernel, all processes are the same— some just happen to share resources.

5. Linux provides an object-oriented device model with device classes, hot-pluggable events, and a user-space device filesystem (sysfs).

6.Linux ignores some common Unix features that the kernel developers consider poorly designed, such as STREAMS, or standards that are impossible to cleanly implement.

7.Linux is free in every sense of the word.The feature set Linux implements is the result of the freedom of Linux’s open development model. If a feature is without merit or poorly thought out, Linux developers are under no obligation to implement it.To the contrary, Linux has adopted an elitist attitude toward changes: Modifications must solve a specific real-world problem, derive from a clean design, and have a solid implementation. Consequently, features of some other modern Unix variants that are more marketing bullet or one-off requests, such as pageable kernel memory, have received no consideration.


Despite these differences, however, Linux remains an operating system with a strong Unix heritage.