4.7. A Description of the different PC and Macintosh Operating Systems

PC is basically the acronym for personal computer that is used by an individual in his home. A PC may either be a desktop computer, a laptop or tablet machine. A PC may be used for any general purpose and some of the most common operating systems for personal computers are Linux, Microsoft Windows and Mac. Most personal computers have options for high-speed internet accessibility and multimedia capabilities.

Personal computers have developed at a fantastic pace and earlier users had to write their own programs. Today, however, there is no dearth of programs for all sorts of tasks from gaming to data management for PCs.

It was in the 1980s that Microsoft and Intel started dominating the personal computer market. Just a few years earlier, Apple Inc. was set up too. Eventually, when Apple launched its own personal computer, the MacBook, apart from its iPods and iPhones, the personal computing market was split into two.

Alongside a media blitz, Apple Inc offered its personal computers with their own Mac operating systems. So, while the rest of the market had personal computers with the Windows operating software, Apple decided to hold its own. Soon, referring to a Mac meant the Apple personal computer and referring to a PC meant referring to a non-Apple personal computer! This has also led to the current confusion about the differences between a PC and a Mac. Essentially, the Mac is a personal computer too! But the branding is what makes all the difference.

Reference:
http://www.differencebetween.net/technology/difference-between-pc-and-mac/

4.6. The Relationship between an Application program, the operating system and hardware

The relationship between an application program and the underlying hardware is usually shown in the form of a stack of layers as shown below:

Application
Application Programming Interface (API)
Operating System
Device Driver
Hardware

Most applications need to know how to talk to the operating system - which is why the operating system will provide a set of programming libraries knows as APIs or SDKs (Software Development Kits) for programmers to use when writing applications.

The APIs sit between the operating system and the running application. The running application relies on the API to perform essential tasks on the computer by telling the operating system what it wants to do - which is why a program that is written to use Windows Vista APIs will not run on an Apple Mac without some kind of emulation or help.

Because there are so many different pieces of hardware, it would be impossible for an operating system to support them all (especially the lesser known devices). That's why hardware manufacturers will write device drivers for different operating systems, so the operating system knows how to talk to the hardware.