Lesson video

Hello, my name is Mrs. Jones, and I'm really pleased that you've decided to learn with me today.

In this lesson, we're going to look at main memory and the different types and the functions, so let's get started.

Welcome to today's lesson.

Today's lesson is called Main Memory from the unit Computer Systems. And by the end of this lesson, you'll be able to describe the purpose of RAM, Rom and cache in a device.

There are four key words to today's lesson.

RAM.

RAM is random access memory, a temporary memory used to store data instructions that the CPU needs while the computer is running.

ROM.

ROM is read-only memory.

It stores essential instructions needed for the computer to start up and operate.

Cache.

Cache is a small storage location for frequently used instructions.

Virtual memory.

Virtual memory is borrowed storage located in secondary storage used when the RAM is full.

There are three parts to today's lesson.

The first is describe the function of RAM and ROM.

The second is explain how cache is used in a device.

And the third is define when virtual memory would be required.

So let's start with describe the function of RAM and ROM.

Inside a computer, the processor needs to use main memory to fetch-execute instructions.

Main memory can also be called primary storage.

It refers to something that is directly accessed by the processor.

RAM and ROM are two types of main memory.

RAM stands for random access memory, and ROM stands for read-only memory.

Both are directly accessed by the CPU.

RAM is faster to access by the CPU than files stored in secondary storage.

RAM is volatile as it requires a constant supply of power to maintain the data stored on it.

When the computer is switched off, all data instructions in RAM are lost.

RAMs temporarily stores all the data and instructions that are currently being processed.

It is read and write access, which means data can be read from and written to memory addresses.

An application is loaded from secondary storage to the RAM when it is in use.

A computer has RAM installed, but you can add more to a computer, as there are usually four slots available on the motherboard.

Sam asks, "Why do I need more RAM in a computer?" Really good question.

As an application runs, the instructions are loaded into RAM from secondary storage.

The CPU then fetches the instructions from RAM and executes them.

If a computer system does not have enough RAM, it will run slowly.

Sam asks, "How do I know if I have enough RAM?" Again, a really good question.

When you buy a computer, it will tell you how much installed RAM there is.

A computer with four gigabytes of RAM will not be able to run as many applications or as fast as 16 gigabytes of RAM.

The more RAM the computer has, the faster it will be.

Let's have a quick check.

What is the function of RAM in a computer? Is it, A, to permanently store all the computer's programmes even when the power is off? B, to store the basic input/output system, the BIOS, and start-up instructions for the computer? C, to temporarily store and hold data and programmes that the CPU is currently using or needs to access quickly? Or D, to perform all the mathematical calculations and logical operations required by software? Pause the video, go back through the slides and consider your answer and then we'll check it.

Let's check your answer.

The answer was C, to temporarily hold data and programmes that the CPU is currently using or needs to access quickly.

Well done if you got that correct.

Unlike RAM, ROM is non-volatile as it still stores the instructions when there is no power.

ROM is read-only.

It cannot be easily changed as it is usually programmed by the manufacturer.

It has a small memory capacity and is located on the motherboard.

ROM stores the BIOS, the basic input/output system, also referred to as the start-up or bootstrap loader.

The ROM has the first instructions to execute to start the computer.

Let's do an activity, and you'll need your worksheet for this.

Complete the table to describe the functions and characteristics of RAM and ROM.

You have a table with RAM and ROM on the left, and you need to add the function and the characteristic.

Pause the video, go back through the slides, use your worksheet and then we'll check your answers.

Let's check your answers.

Let's look at RAM.

The function, RAM is temporary memory used to store data and instructions that the CPU needs while the computer is running.

Characteristics, it is faster to access by the processor than files stored in secondary storage.

It gives read and write access to memory addresses, but is volatile, as everything stored is lost when no power is received.

ROM.

ROM stores essential instructions needed for the computer to start-up and operate.

It stores the BIOS, basic input/output system, also referred to as the startup or bootstrap loader.

Characteristics.

ROM is read-only and cannot be easily changed, as it is programmed by the manufacturer.

It has a small memory capacity and is non-volatile, as it retains the data even without power.

Well done if you got that correct.

Let's move on to the second part of today's lesson, explain how cache is used in a device.

There is one other type of main memory called cache.

This memory plays an important role in improving the performance of a computer system by saving frequently used instructions and data, so they are quickly available for the CPU to fetch.

There are three levels of cache.

Level one cache is usually part of the CPU and has the smallest capacity.

It is the fastest of cache levels, as it is the same speed as the CPU.

You can see on the diagram on the right, level one is inside and is labelled as L1.

Level two cache is usually part of the CPU, but further away than level one cache.

It has a larger capacity than level one.

It is slower than level one cache, but still significantly faster than RAM.

Level three cache is either part of the CPU or near it on the motherboard.

It is the furthest away from the CPU.

It has a larger capacity than level two.

It is slower than level two cache, but still faster than RAM.

Let's have a quick check.

Which cache level is furthest away from the CPU? Is it, A, level one, B, level two, or C, level three? Pause the video, go back through the slides, and consider your answer and then we'll check it.

Let's check your answer.

The answer was C, level three.

Well done if you got that correct.

Let's have another check.

Which cache level has the smallest capacity? Is it A, level one, B, level two, or C, level three? Pause the video, go back through the slides, consider your answer and then we'll check it.

Let's check your answer.

The answer was A, level one.

Well done if you got that correct.

Izzy asks, "How does cache work in the computer?" Really good question.

When the CPU needs data or instructions, it will check through the cache levels before going to RAM.

It will be faster if found in a cache level.

When data is fetched from RAM, it is copied into level three and level two, and finally level one cache, pushing out older, less frequently used data, so it's readily available for future use by the CPU.

Let's do an activity.

Complete the table to show the features of each level of cache.

You have level one, level two and level three down the left, and you need to complete the table to show the features of each level.

Pause the video, go back through the slides, use your worksheet and then we'll check your answers.

Let's check your answers.

Level one cache, usually part of the CPU and has the smallest capacity.

It is the fastest of the cache levels, as it has the same speed as the CPU.

Level two cache, usually part of the CPU but further away than level one cache.

It has a larger capacity and is slower than level one cache, but still significantly faster than RAM.

Level three cache, either part of the CPU or near it on the motherboard.

It has a larger capacity and is slower than level two cache, but still faster than RAM.

Well done if you've got that correct.

Let's look at another activity.

This time, describe why and how cache is used in a computer.

Pause the video, go back through the slides, use your worksheet and then we'll check your answers.

Let's check your answers.

Cache can improve the performance of a computer system by saving frequently used instructions and data, so they are quickly available for the CPU to retrieve.

When the CPU needs data or instructions, it will check through the cache levels before going to RAM.

It will be faster if found in a cache level.

When data is fetched from RAM, it's copied into level three, then level two, and finally, level one cache, pushing out older, less frequently used data so it's readily available for future use by the CPU.

Well done if you got that correct.

Let's move on to the third part of today's lesson, define when virtual memory would be required.

Virtual memory is a memory management technique that allows a computer to compensate when there is not enough RAM capacity by temporarily transferring data from RAM to secondary storage.

You can see here on the diagram, we have RAM on the left, and on the secondary storage that some of it has been now used for virtual memory.

The RAM in a computer has a set capacity limit.

If this is exceeded, the computer slows down, as it cannot run anymore instructions.

Data or instructions that are not actively being used are moved to secondary storage into virtual memory.

Let's have a quick check.

When would virtual memory be used by a computer? Is it A, when the computer is loading the operating system, B, when the CPU needs to perform mathematical calculations quickly, C, when there is not enough RAM to store all active programmes and data, or D, when permanently saving user files like documents? Pause the video, go back through the slides, consider your answer and then we'll check it.

Let's check your answer.

The answer was C, when there is not enough RAM to store all active programmes and data.

Well done if you got that correct.

Any data moved to virtual memory is stored as a page.

When the CPU needs to access the page, it moves it back to RAM and other data is moved to virtual memory or back to secondary storage.

Let's do an activity and you'll need your worksheet.

Explain what virtual memory is and when it would be used in a computer.

Pause the video, go back through the slides, and use your worksheet and then we'll check your answers.

Let's check your answer.

Virtual memory is a memory management technique that allows a computer to compensate when there is not enough RAM capacity by temporarily transferring data from RAM to secondary storage.

Data or instructions that are not actively being used are moved to secondary storage into virtual memory.

Any data moved to virtual memory is stored as a page.

When the CPU needs to access the page, it moves it back to RAM and other data is moved to virtual memory or back to secondary storage.

Well done if you've got that correct.

In summary, RAM is random access memory.

It stores data and instructions currently being processed.

RAM is volatile.

Instructions are lost when there is no power to the computer.

ROM is read-only memory and stores the BIOS and start-up instructions.

It is non-volatile, as it permanently stores instructions.

Cache is faster than RAM but smaller in capacity.

It stores frequently used instructions.

There are three levels with differing speeds and storage capacities.

Virtual memory is used when the RAM cannot store any more data or instructions.

It temporarily stores non-active data in secondary storage as pages.

Well done for completing this lesson on main memory.