Information and Communication Technology (0417) | Storage devices

Welcome to Section 3: Storage Devices and Media!

Hello! In this chapter, we are going to explore where computers keep all their files, programs, and data. Think of storage devices as the filing cabinets or library shelves of a computer system. They allow the computer to remember things, even after it has been switched off!

Understanding storage is vital because the type of storage you choose impacts how fast your computer runs, how much data you can keep, and how easy it is to move that data around. Let's dive in!

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3.1 Understanding Storage: Device vs. Media

Before we look at the different types, it's important to know the difference between a storage device and storage media.

Storage Device

The Storage Device is the hardware component (the machine) that reads data from, or writes data to, the storage media.

• Example: A Blu-ray drive (the machine in the computer)
• Analogy: The CD player itself.

Storage Media

The Storage Media is the physical material on which the data is actually stored.

• Example: A Blu-ray disc (the disc that holds the data)
• Analogy: The CD (the disc containing the music).

Quick Takeaway: The Device *uses* the Media.

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3.2 The Three Families of Storage Technology

All storage technologies can be grouped into three main categories, based on how they save and access information:

1. Magnetic Storage (Uses magnetism to store data)
2. Optical Storage (Uses lasers to read data)
3. Solid-State Storage (Uses electrical circuits; no moving parts)

1. Magnetic Storage Devices and Media

Magnetic storage works by coating a disk or tape with magnetic material. Data is stored by magnetising tiny sections of this material (North or South polarity represent 1s and 0s).

Fixed and Portable Magnetic Hard Drives (HDD)

The most common magnetic device is the Hard Disk Drive (HDD). Inside an HDD, there are spinning metal platters (the media) coated with magnetic material. Read/write heads float just above the platters to access the data.

• Media: Magnetic Hard Disks (Platters)
• Uses: Main internal storage for desktop computers and servers; high-capacity external backups.

Advantages of HDDs:

• Huge Capacity: Can store terabytes (TB) of data (often cheaper per gigabyte than other types).
• Cheap: The most cost-effective solution for storing massive amounts of data.

Disadvantages of HDDs:

• Slower Access: Requires mechanical movement of platters and heads, making it slower than SSDs.
• Fragile: If dropped, the moving parts can easily be damaged (known as a "head crash").

Magnetic Tape Drives

Magnetic tape stores data sequentially on a long strip of plastic film (like an old cassette tape).

• Media: Magnetic Tape
• Uses: Long-term, archival storage, and large-scale corporate backups.

Key Feature: Serial Access

Magnetic tape uses serial access. Analogy: Finding a song on a cassette tape means winding through all the songs before it. This makes it very slow for finding one file, but very effective for writing one massive backup file.

2. Optical Storage Devices and Media

Optical storage uses a laser to read or write data by detecting tiny bumps (pits) and flat areas (lands) on a spinning disc.

Optical Drives and Discs (CD, DVD, Blu-ray)

These devices use different types of lasers to read different density discs.

• Media: CD, DVD, and Blu-ray discs.
• Uses: Distributing software and music, storing video content (movies), small-scale personal backups.

Capacity Comparison (Smallest to Largest):

The main difference between the three types is their data capacity, which comes from how tightly the data is packed on the disc (using different laser wavelengths):

1. CD (Compact Disc): Stores up to 700 MB.
2. DVD (Digital Versatile Disc): Stores typically 4.7 GB (single layer).
3. Blu-ray: Stores typically 25 GB (single layer).

Don't Forget the Types (ROM, R, RW):

• ROM (Read Only Memory): Data is permanently burned onto the disc during manufacture (e.g., a movie DVD). You can only read it.
• R (Recordable): You can write data to it once, but then it cannot be erased or overwritten.
• RW (Re-Writable): You can write, delete, and rewrite data multiple times (slower access than R discs).

Advantages of Optical Storage:

• Highly Portable: Discs are light and easy to carry.
• Cheap Media: Blank discs are very inexpensive.
• Durable: Discs are resistant to magnetic fields (unlike HDDs).

Disadvantages of Optical Storage:

• Low Capacity: Even Blu-ray has relatively low capacity compared to modern HDDs or SSDs.
• Scratch Sensitive: Scratches or dirt can easily corrupt the data and make the disc unreadable.

3. Solid-State Storage Devices and Media

Solid-state storage (often called Flash Memory) stores data using electronic circuits, typically NAND chips. Crucially, there are no moving parts.

Solid-State Drives (SSD) and Portable Drives

Solid-State Drives are replacing traditional HDDs in modern laptops and high-performance computers.

• Devices: Fixed/Portable SSD, Pen drives (USB Flash drives), Flash drives.
• Media: Memory cards (SD, xD, CFast).
• Uses: Operating system storage (due to speed), portable data transfer, cameras and smartphones (using memory cards).

Advantages of Solid-State Storage:

• Extremely Fast: Data can be accessed instantly (random access) without waiting for a head or platter to move.
• Highly Robust/Reliable: Since there are no moving parts, they are very resistant to drops, bumps, and shocks.
• Silent: Produce no noise and generate less heat than HDDs.
• Highly Portable: Pen drives and memory cards are extremely small and lightweight.

Disadvantages of Solid-State Storage:

• Costly: Significantly more expensive per gigabyte than magnetic storage.
• Finite Life: Flash memory cells can only be written to and erased a finite number of times before they wear out. (Modern devices use "wear levelling" to mitigate this, but the limitation still exists).

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3.3 Comparing Storage Technologies (The Exam Focus)

A key skill for IGCSE ICT is being able to compare and contrast these three types of storage based on critical factors. When answering comparison questions, always refer to the specific technology.

Comparison Checklist

1. Speed of Data Access

• Solid-State (SSD): Fastest. Instant electronic access. Ideal for operating systems and frequently used programs.
• Magnetic (HDD): Moderate. Faster than optical, but slowed down by mechanical seeking of data.
• Optical: Slow. Requires the disc to spin up and the laser to track data.

2. Capacity (How Much Data it Holds)

• Magnetic (HDD/Tape): Highest. Can easily store many Terabytes. Tape is excellent for maximum volume backup.
• Solid-State (SSD): High. Getting closer to HDDs, but typically still slightly less capacity and higher price.
• Optical: Lowest. Measured in GBs (max 100 GB for high-end Blu-ray), not TBs.

3. Cost (Cost per Gigabyte)

• Magnetic (HDD): Cheapest. Best value for bulk storage.
• Optical: Cheap media. The discs themselves are very cheap, but the drive unit is an additional cost.
• Solid-State (SSD): Most Expensive. High cost due to complex chip manufacturing.

4. Durability and Reliability

• Solid-State: Best. No moving parts, highly durable against physical shock.
• Optical: Resistant to magnets, but vulnerable to physical damage (scratches).
• Magnetic (HDD): Worst. Very fragile due to precision moving parts; vulnerable to magnetic fields.

5. Access Method

• HDD, Optical, SSD: Use Random Access. You can go straight to the location of the file you want (like finding a page in a book).
• Magnetic Tape: Uses Serial Access. You must read all the data sequentially until you find the file you want (like listening to a cassette tape).

Key Takeaway for Storage Devices

When selecting a storage type, you are always trading off speed, capacity, and cost. If you need speed and robustness (like in a high-performance laptop), choose Solid-State. If you need maximum space for minimal cost (like a server backup), choose Magnetic. If you need cheap, permanent distribution, choose Optical.