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What's Inside My Computer?

What’s inside the PC: The components of a computer
By Gary Warren
Posted: 2023-06-26T22:18:22Z

What’s inside the PC: The components of a computer are the following:

These will be covered in more details in future posts.


- Power Supply Unit (PSU): A device that supplies power to all the components of a computer.

- Motherboard: The main circuit board that connects all the components of a computer together.

- Central Processing Unit (CPU): The brain of the computer that performs most of the processing.

- Random Access Memory (RAM): A type of memory that stores data temporarily for quick access by the CPU.

- Storage Devices: (These are ALWAYS slower than RAM)

- Hard Disk Drive (HDD): A storage device that stores data permanently on spinning disks.

- Solid State Drive (SSD): A storage device that stores data permanently on flash memory chips.

- Optical Drive: A device that reads and writes CDs, DVDs, and Blu-ray discs.

- Video Card or Graphics Processing Unit (GPU): A specialized processor that handles video processing.

- Input Devices: Devices such as keyboards, mice, and touchpads that allow users to input data into a computer.

- Output Devices: Monitors, printers, and speakers that allow users to receive output from a computer.



What happens when we turn on computer?

  •  A PC cannot do anything useful unless it is running its operating system which acts as a supervisor for all software applications. The O/S sets the rules for using memory, drives, and other hardware devices on the computer.


  • Before a PC can run the operating system, it needs some way to load it from disk into RAM. The bootstrap program is a small amount of code that is executed on startup or system boot.
  • The bootstrap is aptly named because it lets the PC do something entirely on its own without any outside operating system - from the term "pulling yourself up by your own bootstraps.



An overview of the Boot-Up process


The boot-up sequence of events in summary is as follows: Turn on Power, the CPU is reset and jumps to an address in the BIOS which runs the POST (Power On Self Test). At the end of POST it transfers to a Bootloader which loads the Operating System


  •  Power supply sends power to the motherboard, which activates the boot process.


  • Power On Self Test instructions are stored in a ROM (Read Only Memory/ aka FLASH Mem) chip, as part of the BIOS (Basic Input Output System)
  • This contains basic information about storage devices, boot sequence, security, Plug and Play (auto device recognition) capability, etc,
  •  In modern computing, ROM is entirely replaced with flash memory, which is cheaply available and can be easily reprogrammed

  •  The BIOS Basic Input Output System initializes and performs a Power On Self Test (POST), which checks the basic hardware components to ensure they are working properly.
  • You may hear your drives spin and see some LEDs flash, but the screen, at first, remains black.
  • Most POST sequences will have a combination of audible and visual messages to let you know what is or isn’t working. These are the beeps you generally hear when the computer is booting up.


  •  The POST tests display adapter. This is the first point you’ll see something appear on your PC’s monitor.


  • The POST checks RAM with a quick read/write operation to ensure that there are no errors in the memory chips. On some PCs you may see a running account of the amount of memory being checked (this can be changed in the BIOS SETUP program)


  • POST checks for keyboards and mouse. Depending upon the type of keyboard you have, you might see the keyboard’s lights flash.

  • At some point you an indication on the screen of how you could enter the BIOS setup program in your computer. Each BIOS software vendor would have a different keystroke

 That ends the POST and the BIOS transfers control to the OS (operating system.)


  •  The OS, such as Windows or macOS, is loaded from the hard drive or another storage device into the computer’s RAM (random access memory).

  • The OS then initializes its own components and drivers and presents the login screen or desktop environment to the user.

  • Generally, the critical parts of the operating system - the kernel - are maintained in RAM as long as the computer is on. This allows the CPU to have immediate access to the operating system, which enhances the performance and functionality of the overall system.


Notes: Your computer can be set to boot from your hard drive, or from your CD or a USB drive or even from the network.

  • If you want to boot from a CD or a USB device, you may need to change the boot order in SETUP.

  • Most computers check their optical drives first. This makes it easier during new installs of operating systems.

  • Then they check their first hard drive, drive 0. POST is looking for the MBR (Master Boot Record).
  • This is always at Cylinder 0, Head 0, Sector 1, or 0,0,1. Once the MBR is found, the control is passed from the POST to the Operating System referenced in the MBR.

YouTube: Motherboards Explained - PowerCert Animated Video

Computer Boot Process Animation