By the end of this lesson you will be able to
- Name the main kinds of storage device and say where each is used.
- Compare SSDs and hard disks for speed, toughness, price and capacity.
- Explain the difference between storage and RAM.
- Find out how much storage your own computer has and how much is free.
- Recognise the warning signs of a failing drive and say what to do next.
Every photo, document and program you own lives on a storage device. Choosing storage is one of the most important decisions when you buy a computer, and losing it is one of the most upsetting things that can happen. This lesson helps you recognise the types, choose sensibly and notice trouble early, so you can protect your files before it is too late.
What storage is for
Storage keeps your information when the power is off. Think of the cupboard from the last lesson. A computer starts by fetching the operating system from storage, and everything you save goes back into it. Storage is measured in gigabytes (GB) and terabytes (TB). A terabyte is about a thousand gigabytes. A typical modern laptop has between 256 GB and 1 TB.
- Very fast
- Typically 4 to 32 GB
- Emptied when power is off
- Holds what is open now
Quick but forgetful.
- Slower than RAM
- Typically 256 GB to several TB
- Keeps data with power off
- Holds files and programs
Slower but permanent.
Read this figure as text
Two columns comparing RAM and storage on purpose, speed, size and what happens when power is lost.
RAM, the short-term workspace: very fast; typically 4 to 32 GB; its contents are lost when the power goes off; holds what you are using right now. Storage, the long-term keeper: slower than RAM; typically 256 GB to several TB; keeps its contents with the power off; holds your files, programs and the operating system. Information moves from storage into RAM when you open it, and back to storage when you save.
The main kinds of storage
A hard disk drive (HDD) stores information magnetically on fast-spinning metal discs read by a tiny moving arm. It is the older technology. It is cheap for the amount it holds, but slower, noisier, and easily damaged by knocks while it is working.
A solid-state drive (SSD) uses flash memory chips and has no moving parts. It is much faster, silent, uses less power and survives knocks better. It costs more per gigabyte, but nearly every new laptop now uses one. SSDs come in a 2.5-inch case connected by a cable (SATA) or as a small stick (M.2) that plugs straight onto the motherboard.
Flash memory is also used in USB flash drives (also called memory sticks or pen drives), which you plug in to carry files between computers, and in memory cards (SD and microSD) used in cameras and phones. An external drive is a hard disk or SSD in its own case that connects by a USB cable, and is often used for backups.
Read this figure as text
A drawn row of storage devices: hard disk, SATA SSD, M.2 SSD, USB flash drive, SD card and external drive, each with a number.
Marker 1: a hard disk drive, spinning magnetic discs, cheap per gigabyte, slower and sensitive to knocks. Marker 2: a SATA solid-state drive, with no moving parts, quicker and tougher. Marker 3: an M.2 SSD, a small stick of flash memory that plugs straight into the motherboard and is very fast. Marker 4: a USB flash drive, a small removable drive for carrying files. Marker 5: an SD memory card used in cameras and phones. Marker 6: an external drive, a hard disk or SSD in its own case connected by a USB cable, often used for backups.
Comparing the choices
| Device | Speed | Toughness | Cost per GB | Common use |
|---|---|---|---|---|
| Hard disk (HDD) | Slow to medium | Fragile when running | Lowest | Bulk storage, backups |
| SSD (SATA or M.2) | Fast to very fast | Good, no moving parts | Medium | Main drive in laptops and desktops |
| USB flash drive | Slow to medium | Small, easy to lose | Medium | Carrying files between computers |
| SD or microSD card | Slow to medium | Small, easy to lose | Medium | Cameras, phones, tablets |
Read this figure as text
A bar chart on a log scale comparing the typical speeds of a hard disk, SATA SSD and M.2 SSD.
Bars on a log scale showing typical reading speed in megabytes per second. A hard disk reads at about 120 MB per second. A SATA SSD reads at about 550 MB per second. An M.2 SSD reads at about 3000 MB per second or more. These are typical figures only; real drives vary, and everyday use is slower than the best figures.
How much storage do you have?
Check your storage
Menu names can change slightly between releases. The ideas stay the same.
On Ubuntu 24.04
Step 1: Open Settings
Press the Super key (the Windows key), type Settings, and press Enter. Or open the system menu at the top right and choose Settings.
Step 2: Open the About page
At the bottom of the list on the left, choose System, then About.
You should see: You should see the device name, memory, processor and a line called Disk Capacity.
Step 3: Note the capacity
Read the Disk Capacity value. This is the total size of your storage drive. Free space is shown in the Files app when you open it and look at the drive details.
On Windows 11
Step 1: Open Settings
Select Start, then Settings. Or press the Windows key and I together.
Step 2: Open Storage
Choose System, then Storage.
You should see: You should see a bar showing how much of your main drive is used, with the amount used and the total size.
Step 3: Read the numbers
Note the used space and the total. If the bar is nearly full the computer may slow down and updates may fail.
When storage starts to fail
All storage wears out eventually. Hard disks fail from mechanical wear and knocks; flash storage fails once its chips have been written to many times, or when its controller fails. Failure is rarely announced, but there are common warning signs. A drive may also keep a health report about itself, called SMART status, which some tools can read.
- Files take a long time to open, or the computer freezes while saving.
- Clicking, grinding or repeated whirring noises from a hard disk.
- Files that disappear, or error messages saying a file is corrupt or cannot be read.
- The computer repeatedly fails to start, or the drive disappears from the list of devices.
- A tool reports the drive's health as warning or failing.
- Warning signs: clicking noises, files will not open, freezes when saving?
- YesCan you still start the computer and see your files?
- YesDo thisCopy the important files to a different drive straight away, then ask a technician to check the failing one.
- NoDo thisSwitch it off and stop trying. Take it to a technician and tell them the files matter.
- NoDo thisCarry on. Keep your backup up to date, since drives can still fail without warning.
- YesCan you still start the computer and see your files?
Read this figure as text
A yes or no decision tree that starts with a possible storage problem and ends with advice such as copy files and ask a technician.
Start: do you see warning signs such as clicking noises, files that will not open, or repeated freezing while saving? If no, carry on and keep your backup up to date. If yes: can you still open your computer and see your files? If yes, copy the important files to another device immediately (a different drive, not the same one), then ask a technician to check the drive. If no, switch the computer off, do not keep trying, and take it to a technician and tell them the files matter.
Common mistakes
✖ Instead of: Buying the largest-capacity hard disk to speed up an old laptop.
✔ Do this: Capacity does not make a computer faster. Replacing a slow hard disk with an SSD does, because the computer reads and writes storage constantly.
✖ Instead of: Keeping the only copy of precious photos on a USB flash drive.
✔ Do this: Flash drives are small, easy to lose and can fail. Keep a second copy elsewhere.
✖ Instead of: Pulling out a USB drive while files are still being copied.
✔ Do this: Use the “eject” or “safely remove” option first, so the computer finishes writing. Otherwise files can be damaged.
If something goes wrong
- I cannot find Disk Capacity on Ubuntu.
- Open Settings, then System, then About. If your release is different, use the search box in Settings and type “About”. Or open the Files app and check the details of the drive.
- My USB flash drive does not appear when I plug it in.
- Try a different USB port, and check it is pushed in fully. Try it on another computer. If it shows nowhere, it may have failed; copy nothing else to it.
- My drive is almost full and the computer is slow.
- Move large files such as videos and photos you want to keep to an external drive, empty the Trash or Recycle Bin and uninstall programs you do not use. Do not delete files you do not recognise.
Key terms
- Storage
- The part of a computer that keeps your files and programs even when it is switched off.
- SSD (solid-state drive)
- A fast storage device with no moving parts that keeps your files when the power is off.
- Hard disk
- A storage device that keeps data on spinning magnetic disks.
- Flash memory
- A type of storage chip that keeps data without power and has no moving parts.
- SMART status
- A built-in health report that a drive keeps about itself, which software can read to warn you of trouble.
Practise it for real
Reading is not the same as being able to do it. Complete these on your own computer, then tick only what you have actually done. These ticks are your own honest record: nothing checks them for you.
Find your storage capacity and free space
Follow the steps for your system (Settings, System, About on Ubuntu; Settings, System, Storage on Windows). Write down the total capacity of your drive and, if your system shows it, the amount used. Work out roughly what fraction of the drive is used. Do not delete anything.
Challenge: choose storage for three people
Write a short recommendation for three people, choosing one storage device for each from SSD, hard disk, USB flash drive or SD card, and explaining why. Person 1 is Amina, who wants her new laptop to start quickly. Person 2 is Joseph, who needs cheap space to keep a copy of 10 years of family photos. Person 3 is Fatuma, who wants to move a few documents from the library computer to her laptop.
Knowledge check
6 questions. You need 80% to pass. Mistakes here are part of learning, and you can retry as often as you like.
Summary
- Storage keeps your information with the power off; RAM does not.
- SSDs have no moving parts and are fast; hard disks are cheaper per gigabyte but slower and more fragile; flash drives and cards are small and portable.
- Check capacity in Settings (System, About on Ubuntu; System, Storage on Windows).
- Clicking noises, unreadable files and repeated freezes are warning signs of a failing drive.
- Do not open a failing drive. Copy what you can and ask a technician.
Checklist: can you do these?
Marking a lesson as read does not prove you can do it. Skills count as demonstrated when you pass the quiz (not yet) and complete the practical tasks (not yet).
Related lessons
References and further reading
Official sources for details that can change between versions.
- Ubuntu documentation (Ubuntu)
- Windows support (Microsoft)