Which of the following statements about computer memories is correct?

The correct answer is: HDDs may experience a "head crash".

To understand why this statement is correct, we need to understand how a Hard Disk Drive (HDD) physically works — and why this makes it vulnerable to a phenomenon called a head crash.

How an HDD Works:
An HDD stores data on one or more rapidly spinning magnetic platters (disks). To read or write data, a tiny component called the read/write head moves back and forth across the surface of these platters. Crucially, the read/write head does not physically touch the platter surface during normal operation — it floats on an extremely thin cushion of air, just a few nanometres above the surface.

What is a "Head Crash"?
A head crash occurs when the read/write head makes unintended physical contact with the spinning magnetic platter. Because the platter spins at thousands of revolutions per minute (typically 5,400 to 7,200 RPM), even the slightest contact can cause catastrophic damage — scraping or gouging the magnetic surface, destroying data, and potentially rendering the entire drive unreadable. Common causes include:

- Physical shock or vibration (e.g., dropping a laptop while it is running)
- Dust or contaminants entering the sealed drive unit
- Manufacturing defects or component failure
- Sudden power loss causing the head to land improperly

This is a real and well-documented risk that is unique to HDDs because they contain moving mechanical parts — specifically, the spinning platters and the actuator arm that moves the read/write head.

Why the Other Options are Incorrect:

Option 2 — "SSDs are also known as volatile memory."
This is false. SSDs (Solid State Drives) are non-volatile storage devices, meaning they retain data even when the power is switched off. Volatile memory refers to RAM (Random Access Memory), which loses all its contents the moment power is removed.

Option 3 — "HDDs do not have any moving parts."
This is false and is actually the opposite of reality. HDDs are famous precisely for having moving parts — the spinning platters and the mechanical read/write head. It is SSDs that have no moving parts, which is why they are faster, more durable, and silent.

Option 4 — "Computers usually have more primary memory than secondary memory."
This is false. In a typical computer, secondary memory (e.g., HDD or SSD storage) holds far more data — often hundreds of gigabytes or several terabytes. Primary memory (RAM) is much smaller in capacity — typically 8 GB to 64 GB in most modern systems. Secondary memory is cheaper per gigabyte and is designed for long-term mass storage, while primary memory is fast but limited in size.

Conclusion:
The only correct statement is that HDDs may experience a "head crash". This is a genuine physical risk resulting from the mechanical nature of HDDs, where the read/write head can accidentally contact the spinning platter, causing severe and often irreversible data loss. This vulnerability is one of the key reasons why SSDs (which have no moving parts and no read/write heads) are considered more physically robust and are increasingly replacing HDDs in modern devices.