The most popular OS today is Microsoft Windows, which has about 85% of the market share for PCs and about 30% of the market share for servers. But there are different types of Windows OSs as well. Some common ones still in use are Windows 98, Windows 2000, Windows XP, Windows Vista, and Windows Server. Each Windows OS is optimized for different users, hardware configurations, and tasks. For instance Windows 98 would still run on a brand new PC you might buy today, but it's unlikely Vista would run on PC hardware originally designed to run Windows 98.
There are many more operating systems out there besides the various versions of Windows, and each one is 
optimized to perform some tasks better than others. Free BSD, Solaris, Linuxand Mac OS X are some good examples of non-Windows operating systems.
Geeks often install and run more than one OS an a single computer. This is possible with dual-booting or by
using a virtual machine. Why? The reasons for this are varied and may include preferring one OS for 
programming, and another OS for music production, gaming, or accounting work. 

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GUI- (graphical user interface) an icon based link between a computer and its operator "Most users prefer an icon-based GUI over a command line option."

 VM- (virtual machine-  a software program which mimics the performance of one or more hardware devices in order to run software independently of the actual hardware "In order to run Java programs in Windows one needs to download an appropriate virtual machine."

X -(X Window System) a software toolkit for UNIX systems underlying numerous GUI window managers including KDE and Gnome "The man was surprised at how similar in functionality X was to Microsoft Windows."

OS- (operating system) a GUI or CLI software link between the computer and operator; also provides a framework for productivity software such as an office suite, web browser, or programming languages "The programmer tested his Java code on many operating systems including: Windows, Linux, and Macintosh."

Linux an open source version of Unix developed by a volunteer team of programmers around the world "Linux was originally developed by Linus Torvalds, who wanted a free Unix-like operating system that ran on standard PC hardware."

CLI (command line interface) a text-only link between a computer and its operator "The technician enjoyed administering the Unix server with the CLI tools."

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A computer would be fairly useless without an OS, so today almost all computers come with an OS preinstalled. Before 1960, every computer model would normally have it's own OS custom programmed for the specific architecture of the machine's components. Now it is common for an OS to run on many different hardware configurations.
At the heart of an OS is the kernel, which is the lowest level, or core, of the operating system. The kernel is responsible for all the most basic tasks of an OS such as controlling the file systems and device drivers. The only lower-level software than the kernel would be the BIOS, which isn't really a part of the operating system. 
The most popular OS today is Microsoft Windows, which has about 85% of the market share for PCs and about 30% of the market share for servers. But there are different types of Windows OSs as well. Some common ones still in use are Windows 98, Windows 2000, Windows XP, Windows Vista, and Windows Server. Each Windows OS is optimized for different users, hardware configurations, and tasks. For instance Windows 98 would still run on a brand new PC you might buy today, but it's unlikely Vista would run on PC hardware originally designed to run Windows 98.

Переклади:
An operating systemis a generic term for the multitasking software layer that lets you perform a wide array of 'lower level tasks' with your computer. By low-level tasks we mean:

1.   the ability to log on with a username and password
2. log off the system and switch users
3. format storage devices and set default levels of file compression
4. install and upgrade device driversfor new hardware
5. install and launch applications such as word processors, games, etc
6. set file permissions and hidden files
7. terminate misbehaving applications

Переклади

log on - to enter information related to an account name and its password in order to access a computer resource "The computer user could not log on because he forgot his username and password." 

multitasking - concurrent execution of two or more tasks by a processor "UNIX is the original multitasking environment and was designed from the beginning to share resources over a network.

log off - to terminate a connection to a computer or network "The server was set to automatically log off users after 10 minutes of inactivity."

file permissions-  a set of strict rules for controlling read, write, and execute access to a file or directory "The company switched from FAT32 to NTFS file system because the former did not support file permissions. " 

format - prepare a device to store data, erasing any existing data "One must format a flash memory drive or a hard disk drive before it can used to store data."

hidden file  - a file which does not appear by default in a directory listing; normally for security reasons or to spare confusion in end users "The administrator was upset when the end user found a way to display and then delete several hidden files." 

kernel  - the fundamental part of an operating system responsible for providing access to the machine's hardware "The system administrator needed to upgrade the kernel in order to provide native support for Serial ATA drives.

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Дай відповіді на питання.
Have you ever written or modified any software? If so, what were the challenges you faced? If not, why not?
Name three pieces of software you use frequently. Why do you use them? What would you change about them?

Pretend you are the world's best programmer and can write computer code as fast as you can think. What kind of software would you write?