What do you call the area where your computer stores program that you are currently running and data that you are currently working on?

Learn more about the startup sequence of a computer.

In this step, you’ll learn how the components of a computer work together from the moment you press the “on” button.

The startup sequence

From the moment you press the power button, a whirlwind of tasks happen inside your computer.

Let’s have a look at each of the components and systems that work together to start up your computer.

CPU

The CPU, or central processing unit, is a large chip inside the computer. This is the brains of the computer: it controls everything. It works by reading instructions and data from the random access memory (RAM), performing an instruction, and then writing the data back to RAM. Some of the instructions may involve other components like the hard drive, but the CPU is in control.

RAM

RAM temporarily stores data while your computer is running.

• RAM is both readable and writable. You can add, change, and delete data stored in RAM.
• It is volatile. When the computer is switched off, all the data stored in RAM is lost.
• It is fast.

ROM

ROM stands for read-only memory. It is a chip containing data installed by the manufacturer that is not typically replaced or upgraded. It stores the BIOS.

• ROM is read-only. It is usually programmed by the computer manufacturer, and cannot be changed or overwritten. (There is a process for overwriting the ROM, called “flashing” it, but it’s difficult and can lead to a completely broken and unrecoverable computer.)
• ROM is non-volatile memory, which means it does not need power to keep the data inside it.
• It is fast.

Hard Drive

The hard drive (sometimes called the hard disk) is the main storage device in your computer. Like RAM, it can be added to and changed, and like ROM it is non-volatile, but it is slow. If you have files and folders on your computer, are stored on the hard drive. The operating system is also stored on the hard drive.

BIOS stands for Basic Input Output System. The BIOS is stored in the ROM. It contains all the basic code for controlling your computer hardware (such as keyboards, mice, monitors and hard drives). After the startup sequence is complete, and control has gone to the operating system, the BIOS does very little.

When you start up your computer, you may see a black screen displaying “Press F2 for Setup”. This is the BIOS. By pressing F2, you enter a setup screen where you can change where the BIOS loads the operating system from.

The operating system is normally stored on the hard drive, but you can load an operating system from a USB drive or a CD instead.

Startup sequence

So, how are these components used in the startup sequence?

• The CPU starts and fetches instructions into RAM from the BIOS, which is stored in the ROM.
• The BIOS starts the monitor and keyboard, and does some basic checks to make sure the computer is working properly. For example, it will look for the RAM.
• The BIOS then starts the boot sequence. It will look for the operating system.
• If you don’t change any of the settings, the BIOS will fetch the operating system from the hard drive and load it into the RAM.
• The BIOS then transfers control to the operating system.

That’s a lot of information and acronyms!

Hopefully, this step has helped you understand what happens underneath the bonnet of a computer when you turn it on. Once you know this sequence, you can create some really fun lesson plans based on it…

An example lesson

Give students or teams of students a component each:

• CPU
• BIOS
• ROM
• RAM
• Operating system

Place them at different tables around the room with some paper. There should be some distance between the students so that everyone can clearly see what’s happening.

Get each team to discuss the key features of their component and write them down on a large piece of paper. They could use their notes, or this could be a test of what they’ve learnt so far.

Run through a simple scenario. For example, “I’m writing a document in Word and my computer crashes. What does RAM do?”

Get the students to physically throw a piece of paper that was on the RAM table into the bin. It’s lost without power. Throw ROM’s data in the bin, and ask the students: is this correct?

Run through the more complicated startup sequence. Have a piece of card with the word CONTROL on it to indicate who has control. Each team has to say what they’re doing as they’re doing it. For example:

I am the BIOS. I’m just going to go over here and check that I have some RAM.

Give a high five to the RAM team

OK, RAM is there. Now I’m going to look for the operating system.

Go over and give a thumbs up to the OS team

I’m going to pick the OS up and put it in the RAM.

The OS team follows BIOS over to the RAM table

Go through several iterations of the startup sequence until the students understand it without looking at their notes. If you can, get them to perform the startup sequence for another class.

Physically modeling the startup sequence is a great learning opportunity for students. Once they can visually see what is happening with the components during startup, they will remember the sequence more easily.

For more detailed descriptions of what’s happening inside some of these components, check out our How Computers Work course.

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Inside a computer

Have you ever looked inside a computer case, or seen pictures of the inside of one? The small parts may look complicated, but the inside of a computer case isn't really all that mysterious. This lesson will help you master some of the basic terminology and understand a bit more about what goes on inside a computer.

Watch the video below to learn about what's inside a desktop computer.

Looking for the old version of this video? You can still see it here: 

Motherboard

The motherboard is the computer's main circuit board. It's a thin plate that holds the CPU, memory, connectors for the hard drive and optical drives, expansion cards to control the video and audio, and connections to your computer's ports (such as USB ports). The motherboard connects directly or indirectly to every part of the computer.

CPU/processor

The central processing unit (CPU), also called a processor, is located inside the computer case on the motherboard. It is sometimes called the brain of the computer, and its job is to carry out commands. Whenever you press a key, click the mouse, or start an application, you're sending instructions to the CPU.

The CPU is usually a two-inch ceramic square with a silicon chip located inside. The chip is usually about the size of a thumbnail. The CPU fits into the motherboard's CPU socket, which is covered by the heat sink, an object that absorbs heat from the CPU.

A processor's speed is measured in megahertz (MHz), or millions of instructions per second; and gigahertz (GHz), or billions of instructions per second. A faster processor can execute instructions more quickly. However, the actual speed of the computer depends on the speed of many different components—not just the processor.

RAM (random access memory)

RAM is your system's short-term memory. Whenever your computer performs calculations, it temporarily stores the data in the RAM until it is needed.

This short-term memory disappears when the computer is turned off. If you're working on a document, spreadsheet, or other type of file, you'll need to save it to avoid losing it. When you save a file, the data is written to the hard drive, which acts as long-term storage.

RAM is measured in megabytes (MB) or gigabytes (GB). The more RAM you have, the more things your computer can do at the same time. If you don't have enough RAM, you may notice that your computer is sluggish when you have several programs open. Because of this, many people add extra RAM to their computers to improve performance.

Hard drive

The hard drive is where your software, documents, and other files are stored. The hard drive is long-term storage, which means the data is still saved even if you turn the computer off or unplug it.

When you run a program or open a file, the computer copies some of the data from the hard drive onto the RAM. When you save a file, the data is copied back to the hard drive. The faster the hard drive, the faster your computer can start up and load programs.

The power supply unit in a computer converts the power from the wall outlet to the type of power needed by the computer. It sends power through cables to the motherboard and other components.

If you decide to open the computer case and take a look, make sure to unplug the computer first. Before touching the inside of the computer, you should touch a grounded metal object—or a metal part of the computer casing—to discharge any static buildup. Static electricity can be transmitted through the computer circuits, which can seriously damage your machine.

Expansion cards

Most computers have expansion slots on the motherboard that allow you to add various types of expansion cards. These are sometimes called PCI (peripheral component interconnect) cards. You may never need to add any PCI cards because most motherboards have built-in video, sound, network, and other capabilities.

However, if you want to boost the performance of your computer or update the capabilities of an older computer, you can always add one or more cards. Below are some of the most common types of expansion cards.

Video card

The video card is responsible for what you see on the monitor. Most computers have a GPU (graphics processing unit) built into the motherboard instead of having a separate video card. If you like playing graphics-intensive games, you can add a faster video card to one of the expansion slots to get better performance.

Sound card

The sound card—also called an audio card—is responsible for what you hear in the speakers or headphones. Most motherboards have integrated sound, but you can upgrade to a dedicated sound card for higher-quality sound.

Network card

The network card allows your computer to communicate over a network and access the Internet. It can either connect with an Ethernet cable or through a wireless connection (often called Wi-Fi). Many motherboards have built-in network connections, and a network card can also be added to an expansion slot.

Bluetooth card (or adapter)

Bluetooth is a technology for wireless communication over short distances. It's often used in computers to communicate with wireless keyboards, mice, and printers. It's commonly built into the motherboard or included in a wireless network card. For computers that don't have Bluetooth, you can purchase a USB adapter, often called a dongle.

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