1.5 - Storage: Internal & External Devices
Primary and secondary storage
Computers need different types of storage to handle data efficiently. Storage is divided into two main tiers based on speed, accessibility, and purpose.
Key differences between primary and secondary storage
- Primary storage - This is fast memory that the CPU (central processing unit) can access quickly, such as RAM (random access memory). It is volatile, meaning data is lost when the power is turned off.
- Secondary storage - This is non-volatile storage that keeps data even when the computer is off. It stores items like applications, user files, and the operating system (OS) for long-term use. The CPU accesses it more slowly than primary storage.
Secondary storage is essential for saving data permanently between computer uses, while primary storage handles data during active processing.
Internal secondary storage devices
Internal secondary storage is built into the computer and provides high-capacity options for everyday use. The two main types are hard disk drives (HDDs) and solid state drives (SSDs).
How hard disk drives work
Hard disk drives (HDDs) are a common type of internal secondary storage. They use magnetic technology to store data.
Key components of HDDs:
- HDDs consist of a stack of magnetised circular metal plates, called platters.
- Each platter is divided into circular tracks and sectors, where data is stored.
- A read/write head floats just above the spinning platters (which rotate at high speed) and moves to the correct track to read from or write to a sector.
Advantages and disadvantages of HDDs
| Aspect | Details |
|---|---|
| Capacity | High, usually measured in gigabytes (GB) or terabytes (TB) |
| Cost | Relatively cheap compared to other options |
| Durability | Long read/write life, but can suffer from fragmentation (where data becomes scattered, slowing access) |
| Other features | Have moving parts, which can make them noisy and prone to damage if shaken |
How solid state drives work
Solid state drives (SSDs) are another type of internal secondary storage that use electronic circuits instead of mechanical parts.
Key features of SSDs:
- SSDs store data using flash memory chips, with no moving components.
- Data is read and written electronically, making the process faster than HDDs.
Advantages and disadvantages of SSDs
| Aspect | Details |
|---|---|
| Capacity | High, but generally lower than HDDs |
| Cost | More expensive than HDDs |
| Durability | No moving parts, so they are silent and more shock-proof (less likely to break if dropped), making them ideal for portable devices like laptops |
| Speed | Much faster read/write speeds than HDDs |
Both HDDs and SSDs can also be used as external devices when connected via ports like USB.
External secondary storage devices
External storage devices allow files to be easily moved between computers. They are portable and connect via interfaces like USB.
Optical discs as external storage
Optical discs are flat, circular storage media that use laser technology to read and write data.
Examples and types of optical discs:
- Examples include CDs (compact discs), DVDs (digital versatile discs), and Blu-Ray discs.
- Types of optical discs:
- Read-only - Data can only be read, not changed (e.g., pre-recorded music CDs).
- Write-once - Data can be written once but not erased (e.g., CD-R).
- Rewritable - Data can be written, erased, and rewritten multiple times (e.g., CD-RW).
Advantages and disadvantages of optical discs:
- They are portable, cheap, and robust (e.g., not damaged by water).
- However, they are less common now due to streaming services for music and films, and many modern devices lack optical disc drives.
External drives and other portable devices
External drives provide high-capacity portable storage.
Types of external storage devices:
- External HDDs and SSDs - These can store very large amounts of data (more than optical discs) and are useful for transporting big files. External HDDs have moving parts, so they are more prone to damage if dropped.
- Other devices - Include USB sticks (also known as flash drives) and SD cards (secure digital cards).
- These are small and compact, often used in devices like cameras and tablets.
- They can hold reasonably large amounts of data despite their size.
Cloud storage as an alternative
Cloud storage is an online service for storing files remotely, rather than on physical devices inside or connected to your computer.
How cloud storage works
- Users upload files to a remote server (a powerful computer) over the internet.
- The server typically uses HDDs or SSDs to store the data securely.
Benefits of cloud storage
- Files can be accessed from anywhere with an internet connection.
- Users do not need to buy expensive physical storage devices.
Drawbacks of cloud storage
- There is often a fee (though some services are free).
- Files cannot be accessed without an internet connection.
- Security is managed by the service provider, which some users prefer (as they handle it), while others dislike losing control over their data protection.