Know and understand solid-state media including memory cards (SD, xD, CFast)

Published by Patrick Mutisya · 14 days ago

ICT 0417 – Storage Devices and Media: Solid‑State Media

3. Storage Devices and Media

Objective

Know and understand solid‑state media, with particular focus on memory cards such as SD, xD and CFast.

What is Solid‑State Media?

Solid‑state media store data in flash memory chips. They contain no moving parts, making them:

  • Resistant to shock and vibration

  • Low power consumption

  • Fast access times compared with magnetic media

  • Compact and lightweight

Common Types of Memory Cards

Card TypeTypical CapacityPhysical Size (mm)Key Uses
Secure Digital (SD)2 GB – 1 TB32 × 24 × 2.1Digital cameras, smartphones, tablets, laptops
microSD2 GB – 1 TB15 × 11 × 1Mobile phones, action cameras, drones
xD‑Picture Card512 MB – 2 GB20 × 25 × 1.8Older Olympus and Fujifilm digital cameras
CFast64 GB – 2 TB42.8 × 36.4 × 3.8Professional video cameras, high‑speed DSLR

Secure Digital (SD) Family

The SD family has three main variants, each defined by capacity and speed class.

  1. SD – up to 2 GB, uses FAT12/16 file system.

  2. SDHC (High Capacity) – 2 GB to 32 GB, uses FAT32.

  3. SDXC (eXtended Capacity) – 32 GB to 2 TB, uses exFAT.

Speed classes indicate the minimum sustained write speed, important for video recording.

  • Class 2, 4, 6, 10 (2 MB/s – 10 MB/s)

  • UHS‑I, UHS‑II, UHS‑III (up to 312 MB/s)

  • Video Speed Class \cdot 6, V10, V30, V60, V90

xD‑Picture Card

Developed jointly by Olympus and Fujifilm, the xD card uses NAND flash similar to SD but with a proprietary interface.

  • Maximum capacity: 2 GB (later versions up to 4 GB, rarely used)

  • Typical speed: 2 MB/s – 6 MB/s

  • Now largely obsolete; replaced by SD and microSD.

CFast Card

CFast is an evolution of the older CompactFlash (CF) standard, using a SATA‑based interface for higher throughput.

  • Interface: SATA 3.0 (6 Gb/s) – theoretical maximum 600 MB/s

  • Typical real‑world speeds: 300 MB/s – 500 MB/s

  • Durable, designed for professional video (4K, 8K) and high‑speed burst photography.

Choosing the Right Card

When selecting a memory card, consider the following factors:

  1. Device Compatibility – Check the device’s specifications for supported card types and maximum capacity.

  2. Capacity Needed – Estimate based on file size (e.g., a 12‑MP JPEG ≈ 5 MB, 4K video ≈ 350 MB/min).

  3. Speed Requirements – For video, match the card’s speed class to the recording bitrate.

  4. Reliability – Look for cards with error‑correction code (ECC) and a good warranty.

Data Safety and Management

Solid‑state cards are non‑volatile, but they can still suffer from data loss due to:

  • Physical damage (bending, crushing)

  • Electrical static discharge

  • Corruption from improper ejection

Best practices:

  1. Always use the “Safely Remove Hardware” function before unplugging.

  2. Back up important files to a computer or external hard drive regularly.

  3. Store cards in anti‑static sleeves when not in use.

Suggested diagram: Cross‑section of an SD card showing NAND flash chips, controller, and contact pads.

Summary

  • Solid‑state media use flash memory, offering speed, durability, and compactness.

  • SD (including SDHC/SDXC) dominates the consumer market; microSD provides an even smaller form factor.

  • xD cards are largely obsolete but were once used in Olympus/Fujifilm cameras.

  • CFast cards provide professional‑grade performance for high‑resolution video and fast burst photography.

  • Choosing the correct card involves matching capacity, speed class, and device compatibility.