A central processing unit controls the functions of most electronic products. Usually called a CPU, this component accepts input data, processes information and sends it to whatever component that is in charge of executing the action. CPUs are also known as microprocessors and are at the center of any computer system. Although CPUs are most often thought of as a computer chip, they can also be found in many other electronic devices including cell phones, handheld devices, microwaves, television sets and toys.
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  • Modern CPU evolved from miniature transmitters and integrated circuits developed in the early 1960s by IBM and other top technology companies of the time. By the early 1970s, transmitting integrated circuits were being manufactured commercially; engineers based CPUs on that technology. Harnessing the transmission abilities of integrated circuits, they added the ability to process information and memory power. Combined, these elements became the core of the CPU. By the end of the 1970s technology had reached the point where CPUs could be commercially produced and were the size of a fingernail.

    During the 1980s, CPUs became a standard component in consumer electronics. They could be found in cameras, television sets and pocket calculators. By the next decade, the small size and cheap production cost of the CPU allowed computers to cross over from industry to the home. Today, engineers continue to fine tune CPUs, making them ever smaller and more powerful.

CPU Parts
CPUs are made up of six key components that work in combination to process and execute commands. First, the control unit is the brain of the CPU. This part receives the input data and decides where to send the processed information. Second, the instruction cache is where the control unit’s instructions are stored. Specific instruction data is loaded into the CPU when it is manufactured. Third, the prefetch unit is the information portal. Input data goes through the prefetch, which stores a copy of the data before sending it on to be processed by the control unit. Fourth, the decode unit translate the input instruction into binary code, which is then sent on to the fifth component, the arithmetic logic unit. The ALU receives the code from the decode unit and chooses the action needed to carry out the command. Sixth is the CPU's memory cache. Here, all information that has been sent, received or preloaded is stored.

A CPU performs a series of steps to execute a command. Each command is handled individually and a CPU can process multiple commands in a matter of seconds. The more powerful the CPU, the faster the commands are processed. A command is issued by the system user using an input device such as a keyboard or mouse. Next, the command is sent to the prefetch unit. The unit accesses the preloaded CPU memory to identify the command and sends it to the command unit. Next, the command unit determines what steps come next. This data is passed on to the decode unit, which transfers the data into binary code and sends it to the ALU, next, the ALU changes the raw data into an actual command. Next, the ALU sends a copy of the command to the RAM or ROM before sending it back to the command unit, which sends the code to the part of the system that will actually perform the action. Finally, the action is executed and the result is sent back to the user.

There are different types of CPUs; each type comes with varying degrees of speed memory and preset instructions. The larger the CPU, the faster it can process, store and execute commands. A single-core CPU is the smallest unit available. It is usually found in smaller appliances that only perform a simple set of actions such as a remote control or toy. Dual-core CPUs contains two command units and contain enough power and memory for most personal computers. Multi-core CPUs contain multiple command units. They are mainly used by large industrial electronic devices, servers and network workstations.

CPU size refers to the unit’s power to perform tasks and the amount of memory space it contains. CPU size is measured in binary digits and are called bits. Originally, CPUs contained four bits but modern CPUs have eight. Eight-bit CPUs are the smallest and slowest modern components available and are used mostly in toys or household appliances.
Sixteen-bit and 32-bit have become the standard CPU size and can be found in personal computers, laptops, cell phones and other electronic devices that can perform a variety of tasks. Sixty-four-bit CPUs are becoming increasingly popular in high-end personal computers and laptops. Larger CPUs exist; these are usually used for industrial purposes.

References : Introduction to Microprocessors and Micro controllers, 2004; John Crisp

Viruses will affect your PC in 4 different ways . . .
  1. The Boot Sector:
The boot sector is where your operating system files reside on your floppy or hard disk. A virus will go to that location on your disk and corrupt these files (IO.SYS, MSDOS.SYS, and COMMAND.COM) so that your PC will NOT boot up as expected.
           EXAMPLE: the STONED virus.

2      The File Allocation Table: The File Allocation Table (FAT) is a list

The File Allocation Table (FAT) is a list of all the files on your floppy or hard disk, and where the files are physically located on the disk. A virus will corrupt the FAT so that you cannot locate or access your files.
          EXAMPLE: the CASCADE virus.

3        The Partition Table

The partition table on your HARD DISK tells MS-DOS how big your hard
disk is, and what percentage of it is used by MS-DOS. A virus can corrupt
your partition table, which wipes out ALL of your files in an instant.

4       .COM and .EXE Files

Files with these extensions are EXECUTABLE files, which perform a
specific action. A virus can attach itself to one of these kinds of files and
corrupt the way it operates.
EXAMPLE: the 4096 virus.