Title: Know storage capacity measurements: bit, byte, KB, MB, GB, TB.
Course: Module 1, Concepts of Information and Communication Technology (ICT)

Introduction

At some point in time, most of us have come across a situation where a drive or disk being used run out of space.

In this Lesson, we take a look at how manufacturers rate the capacity of storage devices such as hard drives, floppies, flash media and compact disks and their actual size.

Bits and Bytes

All computer data is stored in a binary format as either a one or zero.

Eight of these bits together form the most commonly referred to item in computing, the byte.

The various amounts of storage capacity are referred by a prefix to represent a specific amount, similar to the metric prefixes.

Since all computers are based on binary math, these prefixes represent base 2 amounts.

Each level is an increment of 2 to the 10th power or 1,024.

Definitions of sizes

People often get confused about storage sizes, because the different words all sound a little similar. However, it is quite easy once you know... look at the table here:
- 1 Kilobyte (Kb) = 1,024 Bytes
- 1 Megabyte (Mb) = 1,024 Kilobytes (or 1,048,576 Bytes)
- 1 Gigabyte (Gb) = 1,024 Megabytes (or 1,073,741,824 Bytes)
- 1 Terabyte (Tb) = 1,024 Gigabytes (or 1,099,511,627,776 Bytes)

Sometimes the abbreviations are written in capitals, e.g. KB=Kb, MB=Mb, GB=Gb, and TB=Tb.

To give you some idea of how this relates to things you know...
- A CD-ROM holds around 800Mb (megabytes)

- RAM in a modern desktop or laptop computer is usually 1Gb to 2Gb (gigabytes) these days.

- A standard DVD holds around 4.3Gb (gigabytes) of data

- A hard disk in a modern laptop can usually store between 120Gb and 250Gb (gigabytes).

- Only computer servers would have a Terabyte of storage, and most servers, in a typical company for example, are much smaller than that !

Why is it important?

This is very important information because when a computer operating system or program reports the available space on a disk drive, it is going to report the overall total of available bytes or reference them by one of the prefixes.

So when you look at your disk drive it might say something like:
- Total disk size 120Gb
Free space 9Gb

So, you now know that the space you have available on this disk is about the same as two DVD's worth of information, 4.3Gb x 2 = 8.8Gb.

Or, you might be burning a CD-ROM with data, and have files that are 900Mb in size... but now you know that only 800Mb will fit! ;-)

What is a megabyte

How is megabyte often written?

- Mb
Feedback: Correct!
- MegaB
Feedback: Incorrect :-(
- M-BITE
Feedback: Incorrect :-(