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A  digital computer typically consists of a control unit, an arithmetic-logic unit, a memory unit, and input/output units, as illustrated in the figure. The  arithmetic-logic unit (ALU) performs simple addition, subtraction, multiplication, division, and logic operations—such as OR and AND. The main  computer memory, usually high-speed  random-access memory (RAM), stores instructions and data. The control unit fetches data and instructions from memory and effects the operations of the ALU. The control unit and ALU usually are referred to as a processor, or  central processing unit (CPU). The operational speed of the CPU primarily determines the speed of the computer as a whole. The basic operation of the CPU is analogous to a computation carried out by a person using an arithmetic calculator, as illustrated in the figure. The control unit corresponds to the human brain and the memory to a notebook that stores the program, initial data, and intermediate and final computational results. In the case of an electronic computer, the CPU and fast memories are realized with transistor circuits.

I/O units, or devices, are commonly referred to as computer peripherals and consist of input units (such as keyboards and optical scanners) for feeding instructions and data into the computer and output units (such as printers and monitors) for displaying results.

In addition to RAM, a computer usually contains some slower, but larger and permanent, secondary memory storage. Almost all computers contain a magnetic storage device known as a hard disk, as well as a disk drive to read from or write to removable magnetic media known as floppy disks. Various optical and magnetic-optical hybrid removable storage media are also quite common, such as CD-ROMs (compact disc read-only memory) and DVD-ROMs (digital video [or versatile] disc read-only memory).

Computers also often contain a cache—a small, extremely fast (compared to RAM) memory unit that can be used to store information that will be urgently or frequently needed. Current research includes cache design and algorithms that can predict what data is likely to be needed next and preload it into the cache for improved performance.

Here's an example of the main components of a computer and their functions in tabular format:

Component	Function
Central Processing Unit (CPU)	The "brain" of the computer, responsible for executing instructions and performing calculations
Memory (RAM)	Temporary storage for data used by the CPU
Storage (Hard Drive or SSD)	Long-term storage for data and programs
Motherboard	The main circuit board that connects all the components of the computer
Power Supply	Provides power to the components of the computer
Video Card	Handles the display of images on the monitor
Network Card	Enables communication with other devices over a network
Input Devices	Allows the user to input data, such as a keyboard and mouse
Output Devices	Allows the computer to output information, such as a monitor or printer

here are some additional components that can be part of a computer and their functions:

Component	Function
Optical Drive	Reads and writes data on CDs, DVDs and Blu-ray discs
USB ports	Allows connection of external devices such as a flash drive or external hard drive
PCI/PCIe slots	Allow for the addition of expansion cards such as a sound card or network card
Cooling system	Keeps the internal temperature of the computer at a safe level
Battery	Provides power to the computer when it's not connected to an outlet
BIOS/UEFI	firmware that controls the basic input/output functions of the computer
Sound Card	Enables the computer to play and record audio
Display Port	Connects the computer to a monitor or other display device
Thunderbolt Port	Connects the computer to external devices such as hard drives or displays at high speeds

here are some additional components that can be part of a computer and their functions:

Component	Function
Graphics Card	Handles the rendering of 3D graphics and video
Firewire port	High-speed data transfer interface for external devices
Memory Card Reader	Reads and writes data to various types of memory cards
eSATA port	High-speed data transfer interface for external hard drives
ExpressCard slot	Allow for the addition of expansion cards such as a network card, sound card or other peripheral devices
Fingerprint scanner	Provides an additional security layer by allowing the user to log in with a fingerprint
SmartCard Reader	Reads and writes data to smart cards used for security and identification purposes
Wifi/Bluetooth card	Enables wireless connectivity to networks or other devices
Touchpad	Allows the user to control the cursor on the screen using finger gestures

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