In this video we're exploring the measurements of data capacity. We already understand that everything stored in a computer system is stored in binary, those zeros and ones that represent just two states. For example, capacitors that store a charge or don't store a charge in RAM.
to represent a 1 or a 0. Magnetic north and south poles in hard drives. Pits and lands on blu-ray disks. Current or no current with logic gates. This is because it's much easier, and therefore cheaper, to manufacture electronic component units with just these two states.
However, this means that everything, literally everything, must be stored with only zeros and ones. known as a bit or a binary digit. It is clear that Boolean values true and false, or on and off, can be stored with just one bit. However, to store more complex types of data, we need to use a combination of bits. For example, a single digit LCD display requires four bits of data.
I will explore how and why that is the case in a later video about binary numbers. Those four bits are called a nibble because they're half a byte. And yes, this is because computer scientists somehow think they have a sense of humour. Therefore, a byte is eight bits. Those eight bits can be used to represent lots of different types of data.
For example, it could be a number. It could also be a letter or a symbol if every letter had its own binary sequence. Equally, it could be part of a picture or a sound file. This is exactly how computers work, and we'll explore each of these concepts in more detail in other videos in this unit.
A single byte, whilst useful for storing a single character, is not enough for other types of data, and therefore computers started using thousands of bytes of data called kilobytes. As the binary system is a base two number system, these larger units are two to the power ten units. Two to the power of ten is a thousand and twenty four, so a kilobyte is actually a thousand and twenty four bytes and not a thousand. Now this doesn't make much a huge amount of cents when you're taught in maths and science that a kilo is a thousand. Therefore, we tend to approximate a kilobyte to 1000 bytes just for simplicity.
Even 1000 bytes is not enough capacity to store most files, therefore we have a need for higher units of measurement. Here are the units of measurements you need to know for the GCSE exams. You will notice that the binary values of these units calculated by powers of 1024. Therefore, a megabyte is 1024 multiplied by 1024 bytes.
Or expressed another way, 1024 to the power 2, which is 1048576 bytes. We're also able to express these as decimal values calculated by powers of 10. For example, a megabyte is 10 to the power of 6. or 1 million bytes. It is fine for GCSE to be using these decimal approximations.
In actual fact, hard disk suppliers today have started using these values because it makes more sense to consumers. So today it's possible to have a hard drive of 500 gigabytes and actually have 500 billion bytes on the drive. So you see that 1024 or 1000 is a kilobyte. 1024 or 1000 kilobytes is a megabyte.
1024 or 1000 megabytes is a gigabyte. 1024 or 1000 gigabytes is a terabyte. And 1024 or 1000 terabytes is a petabyte. Now in order to explain the background to all this, this video has become a little more complex than it really needs to be for your exams. For the purpose of exams it's probably easy to remember the sequence kilo mega giga terra peta If you know that a kilo is a thousand, three zeros, just add three zeros each time to the unit.
Therefore a mega is six zeros, a giga is nine, a tera is twelve and a peta is fifteen zeros. Often in exams you have to convert from one unit to another. For example, a 500 gigabyte SSD is 0.5 or half a terabyte. It is also 500,000 megabytes. To convert between the units, it's handy to remember you either multiply or divide by a thousand.
Remember that a byte is eight bits. So if you need an answer in bits, you need to multiply by eight. Here is this concept in action.
OK, so let's look at some real examples. Here we can see a list of files in a typical file storage system. We've hidden the file name so we can focus on what's important. If we take the top one, we have a Microsoft Word document which is 1470 kilobytes.
If we wanted to know what that was in megabytes, then we're going to divide by a thousand. So that's 1.47 megabytes. Further down here we have a Microsoft PowerPoint file. which is 740 kilobytes. Again if we divide by a thousand that is 0.74 megabytes.
So it's quite straightforward to convert between the two units here. Typically once we go above a thousand we want to represent the data in the higher unit. In a similar way here we have an Excel document which is just 25 kilobytes. If you want to know how many bytes that is, then it's 25,000 bytes. That's because a kilo is a thousand.
If we want to know what it is in bits then we take our 25,000 and multiply it by eight. It says eight bits in a byte. What comes next is technically a little beyond what you need to know for the GCSE exam so there's no need to take notes on the rest of this video. It's worth watching however. as it helps to clear up some common misconceptions.
So our final observation is the symbol for each of these units, KB, MB, GB, TB and PB, and these are shown in capital letters because they're representing bytes, not bits. Confusingly, the capacity of drives and the size of files is measured in bytes using capital letters, But the data transfer speeds over network are measured in bits per second using a lowercase second letter. Therefore 1MB is not the same as 1MB.
It's eight times bigger.