A1.1.7 Describe internal and external types of secondary memory storage.

📚 You can find additional information in the course companion pages 25 to 28

The Big Idea

While primary memory (such as RAM and registers) provides fast but temporary data access, secondary memory offers non-volatile, long-term storage for programs, files, and the operating system itself. Secondary memory is broadly categorized into internal and external storage types, each with distinct characteristics, interfaces, and usage scenarios.

This article provides a structured overview of internal and external secondary storage types, their underlying technologies, and when each is most appropriately used.

 

1. Internal Secondary Memory Storage

Internal storage refers to memory devices that are physically integrated inside the computer or device chassis. These storage components are connected directly to the system's motherboard, usually via SATA, NVMe, or eMMC interfaces. You should probably read this article about NAND memory and SSD's

a. Hard Disk Drives (HDDs)

• Technology: Magnetic spinning platters with read/write heads.
• Typical Capacity: 500 GB – 20 TB.
• Speed: Slower than SSDs (~80–160 MB/s).
• Advantages: High capacity at low cost per gigabyte.
• Use Cases:
  • Desktop and laptop storage (especially budget or archival).
  • File servers or media storage in environments where speed is less critical.

b. Solid State Drives (SSDs)

• Technology: NAND flash memory with no moving parts.
• Typical Capacity: 128 GB – 4 TB (consumer-level).
• Speed: Much faster than HDDs (up to ~3,500 MB/s via NVMe).
• Advantages: Fast boot times, silent operation, shock resistance.
• Use Cases:
  • Operating system and applications for rapid loading.
  • Gaming, development, content creation, and general-purpose laptops.

c. Embedded MultiMediaCard (eMMC)

• Technology: Flash memory soldered directly onto the motherboard.
• Speed: Slower than SSDs, faster than traditional SD cards.
• Advantages: Low power consumption, small form factor, inexpensive.
• Use Cases:
  • Smartphones, tablets, Chromebooks, and entry-level laptops.
  • Devices where compact size and low cost are more important than high performance.

 

2. External Secondary Memory Storage

External storage devices are physically separate from the main system unit and typically connected via USB, Thunderbolt, Ethernet, or Wi-Fi. They allow data transfer, backups, portability, and extended capacity.

a. External HDDs and SSDs

• Technology: Same as internal versions, packaged with external interfaces (usually USB 3.x or USB-C).
• Use Cases:
  • Backups, portable storage, media libraries.
  • Large data sets for transfer between computers.
  • SSDs are preferred when speed and reliability are required (e.g., professional video editing).

b. Optical Drives (CD/DVD/Blu-ray)

• Technology: Laser-based reading and writing on optical discs.
• Advantages: Long shelf life (archival storage), low cost per disc.
• Limitations: Low capacity (~700 MB–25 GB), slow access, and becoming obsolete.
• Use Cases:
  • Legacy systems, physical media distribution, archival data (e.g., legal, medical).

c. Flash Drives (USB Thumb Drives)

• Technology: NAND flash memory with USB interface.
• Typical Capacity: 8 GB – 512 GB.
• Advantages: Extremely portable, plug-and-play, no external power.
• Use Cases:
  • Quick file transfers, bootable OS images, student and office use.

d. Memory Cards (SD/microSD)

• Technology: Flash storage used with card readers.
• Advantages: Small size, moderate speed, wide compatibility with consumer devices.
• Use Cases:
  • Cameras, phones, drones, Raspberry Pi, embedded systems.

e. Network Attached Storage (NAS)

• Technology: One or more HDDs/SSDs connected to a local network via Ethernet or Wi-Fi.
• Advantages: Centralized storage accessible by multiple devices.
• Use Cases:
  • Home media servers, small business backups, surveillance video storage.
  • Collaboration tools for shared access in teams.

 

Summary Table: Internal vs. External Secondary Storage

Type	Internal / External	Speed	Portability	Common Uses
HDD	Both	Low	External HDD: portable	Archiving, large storage
SSD	Both	High (esp. NVMe)	External SSD: portable	OS drives, fast access storage
eMMC	Internal	Medium–Low	Fixed	Embedded systems, low-end laptops
Optical Drive	External (mostly)	Very Low	Portable	Archival, legacy media
Flash Drive	External	Medium	Highly Portable	Quick file transfers, temporary storage
Memory Card	External	Medium	Highly Portable	Cameras, mobile devices, embedded systems
NAS	External (networked)	Variable (depends on network)	Stationary	Shared storage, media streaming, backups

 

Choosing the Right Storage: Usage Scenarios

• High-performance computing: Use NVMe SSDs internally for OS and applications.
• Backup and long-term storage: Use external HDDs or NAS systems.
• Lightweight mobile devices: Use eMMC for space and power efficiency.
• Collaboration and sharing: Use NAS with cloud-like access across devices.
• On-the-go transfers: Use USB flash drives or memory cards.
• Media consumption and archival: Use external optical drives if needed, though this is increasingly rare.

---

Conclusion

Secondary storage comes in many forms, each suited to different trade-offs between speed, capacity, cost, and portability. Internal storage prioritizes performance and permanence, while external storage offers flexibility, expandability, and physical data transport. Understanding the differences allows system designers, users, and administrators to choose the right storage solution for each scenario—from enterprise backup systems to mobile devices.