Operating System

Linux is an operating system. It has the goal of managing the resources of your computer. In particular, if you look at the source code [7] you'll find that it breaks down into several parts, thus: initialization is the process that happens when you power-on your computer. The kernel initialization code parses the command line options, calibrates the speed of the machine, initializes various tables, and starts the first ``program'' running (called init). The init program then reads configuration files and starts other programs. (see [7] pp443-450).

• system calls are a set of services that the operating system provides to user programs. System calls allow you to do things like read the time from the hardware clock. Since the hardware clock is shared by all running programs access to the clock has to be managed. (see [7] pp451-458)
• signals, interrupts, and time are the primary tools to allow the operating system to make it appear that there are multiple programs running in parallel. The resources of the computer are time-sliced and scheduled in very small increments to give the impression of many things happening at once. (see [7] pp459-478)
• processor or CPU (central processing unit) is managed by the operating system and is allocated among the many processes and threads. Linux maintains priorities and schedules use of the processor. (see [7] pp479-498)
• memory in a computer forms a hierarchy. There are registers within the CPU, two or three levels of cache where level 1 cache is faster than level 2 cache. Level 2 cache is faster than level 3 cache. Beyond the cache is slower main memory. And beyond main memory is the hard drive which is the slowest of all the devices (see [7] pp499-520) (refrigerator story).
• devices that are attached to the computer are next. Examples of devices are your keyboard, screen, speakers, PCMCIA cards, etc. Since access to these devices need to be shared the operating system manages them. Linux has a fairly uniform way of handling most device drivers that are dynamically loaded as needed. (tables story)