Topic 2c – Memory and Storage

Spinning platters, laser-read discs, and silent silicon — three technologies, each the best answer to a different question.

Learning Objectives

By the end of this topic, you should be able to:

Learning Activities

To help you meet the learning objectives, we have prepared a combination of readings, activities, and videos.

Course Readings

These reading were designed to introduce the course topics to an audience of educators. They should be considered "required" and read in order.

Supplemental Readings

Some participants find it helpful to read about a topic from a source written for a slightly more technical audience. These supplemental readings cover similar material as the course readings but may not fully align with the course learning objectives. Use them as an optional complement to your study, not a substitute for the course readings.

Lesson Videos

These videos support the readings above and may present the material with some deeper connections and worked examples.

Checking for Understanding, Questions

Review the Learning Objectives at the top of this page. You will be asked to demonstrate these skills on this week's competency demo. To check your understanding, try the following questions. Try each one on your own before looking at the answer key. It is completely fine if you need to revisit the readings as you work through these questions.

Storage Characteristics

  1. In one sentence each, describe the physical basis of magnetic, optical, and flash storage. What does each one actually do to store a 0 or a 1?
  2. Explain how an HDD fails and how an SSD fails. What is fundamentally different about the two failure modes?
  3. Why does Blu-ray hold more data than a DVD even though the disc is the same size?

Choosing the Right Storage

  1. A school district needs to archive ten years of security camera footage. Cost is the primary constraint. Which storage type would you recommend, and why?
  2. A teacher wants to distribute a fixed set of curriculum materials to students who may not have reliable internet access at home. Which storage type makes the most sense, and why?
  3. A student argues that HDDs are obsolete because SSDs are faster. How would you respond?

Checking for Understanding, Answers

You can compare your answers to the following answer key.

Show Answer Key

Storage Characteristics

  1. Magnetic (HDD): A read/write head magnetizes tiny regions of a spinning metal platter in one of two orientations to represent 0s and 1s.
    Optical (CD/DVD/Blu-ray): A laser reads microscopic pits and lands (flat areas) on a reflective disc surface; the difference in reflection represents 0s and 1s.
    Flash (SSD/USB drive): Electrical charges are trapped in floating-gate transistors; the presence or absence of a charge represents 0s and 1s, with no moving parts involved.
  2. HDD failure is typically mechanical: the spinning platters or the read/write head physically wear out or crash. Failure is often sudden and catastrophic — a head crash can destroy data instantly. SSD failure is gradual and electronic: flash cells can only be written a finite number of times before they wear out. SSDs usually degrade slowly and may give warning signs before failing completely. (When an SSD reaches its write limit, it often goes into 'Read-Only' mode—meaning you can still save your files to another drive, even if you can't add anything new to that one.) The fundamental difference is mechanical vs. electronic wear.
  3. Blu-ray uses a shorter-wavelength laser (blue-violet, 405 nm) than DVD (red, 650 nm). A shorter wavelength means the laser spot can be focused more precisely, allowing the pits and lands on the disc to be packed more tightly. More data fits in the same physical space.

Choosing the Right Storage

  1. Magnetic storage (HDD) is the best fit. HDDs offer the lowest cost per gigabyte of any storage class, which matters most when archiving large volumes of video footage that will rarely be accessed. The lower speed of HDDs is acceptable for archival use where fast retrieval is not the priority.
  2. This is a design choice with both optical storage (DVDs or Blu-ray) or flash storage (USB drives) being reasonable answers. Optical media is inexpensive and read-only once burned, which prevents accidental modification. Flash drives are more convenient and reusable. The key point is that secondary storage that does not require internet access is the right category; either answer is defensible with a clear reason.
  3. HDDs are not obsolete — they remain the best choice for high-capacity, low-cost archival storage. SSDs are faster and more durable for active use (laptops, operating system drives), but for storing large amounts of data cheaply (servers, video archives, backups), HDDs are still the most cost-effective option. "Better in one way" does not mean "better in every context."

Extend Your Learning

The following resources go a little deeper on topics we touched on but did not fully explore in the readings. These are entirely optional — none of this material appears on the Competency Demo — but each one is a natural "next question" from something covered this week.

  • RAID: turning many drives into one reliable system
    How do servers use multiple drives together to improve reliability and performance? RAID (Redundant Array of Independent Disks) turns the failure characteristics of HDDs into a manageable engineering problem rather than a crisis. This article from Western Digital covers the common RAID levels and what each one protects against.
    RAID Levels Explained — Western Digital