Installing Operating System (OS) needs registration to function fully. Maybe, you install unregistered OS that's why it comply the needs of CD. I suggest you reformat it. Buy the retail OS (if can't afford crack your OS out) so it won't ask you again about the OS error.
No it is a Windows PC. Apple computer run the OSx operating system which is currently called Snow Leopard.
An Operating system is a software that controls the computer's hardware and softwares. In Windows, there are many operating systems, such as: -Windows 10 -Windows 8.1/8 -Windows 7 - (Continues to older versions) -Vista/Xp/Home Basic/Xp Professional/2003 etc.
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The computer is running on the Windows operating system.
Professional
Windows XP Professional is an operating system.
Windows laptop computer refers to the operating system in the computer. This operating system is where your virtual memory, task, and files are stored.
...with Windows XP Professional already installed on your computer. Windows Vista cannot be installed without Windows XP Professional installed first on your computer, it's the same with Windows 7; Windows' latest operating system (OS).
To install more than one operating system on a computer, it is best to start with the oldest first. For example, if you are installing Windows 98 and Windows XP on a computer, install the Windows 98 first. Put the installations on separate partitions. This will prevent conflicts between the two. Once you have installed the second operating system you will find that each time you start your computer, you are given the option of which operating system to invoke. Remember that if you have a Windows XP partition with files that you want to access from the Windows 98 (or Linux) installation, choose the FAT32 file system when installing XP. Windows 98 and some versions of Linux cannot access files on an NTFS partition.
The operating system
Installing any pirated software leaves you at risk of prosecution and the seizure of your computers (depending on your location). Installing any version of Windows (legitimate or otherwise) on a Mac means that it is liable to be infected with the thousands of viruses that exploit the Windows operating system. A pirated version of Windows may well include code that will be exploiting and compromising your computer.
A standard Apple Macintosh computer uses Apple's own operating system called Mac OS X. You can install Microsoft's Windows operating system (or many other operating systems) onto a Mac with an Intel processor if it is required. Installing the Windows system will leave your Mac vulnerable to the thousands of Windows viruses that do not affect Mac OS X.