3. Answer the following questions. 1 What is the difference between UNIX and Linux? 2 3 4 Choose one of the words in italics in the text. What is the definition of the word you have chosen? What are the three levels of a Linux system? What are the two main functions of the kernel? [Reading Text] UNIX was initially developed by researchers at Bell Labs in the 1970s. Today, UNIX and its variants are widely used mainly on servers. By far, the most well- known UNIX-like operating system is Linux. Linux is available in different distributions which include the Linux kernel and different collections of software. These distributions have various user interfaces, many experienced users preferring the command-line interface, or shell. Linux distributions include a range of software including text editors. memory. While the mechanics of Linux and other Unix operating systems are complicated, the components of a Linux system can be grouped into three levels. The lowest level is the hardware, such as Central Processing Unit (CPU) and The next level is the kernel. It enables communication between hardware and software, by providing instructions to the CPU and other hardware. The programs that are running on the system, or processes, make up the top level known as the user space. Processes in user space generally only have access to a restricted amount of memory and operations, this is called user mode. The kernel runs in kernel mode which allows it unrestricted access to hardware resources. The kernel provides functions such as process management and memory management. A computer only has limited Random Access Memory (RAM) and processor cores. Process management allows the system to run multiple programs (processes) at the same time even if the CPU can only execute only a few processes at a time. Memory management allows applications to share the system's memory while avoiding potential issues such as memory leak. Included with the kernel are device drivers that provide an interface for applications to communicate with hardware, such as hard drives. System calls allow user processes to access features that are executed at kernel mode, for example creating new processes.