What Is An SD Card?

Date First Published: 29th August 2023

Topic: Computer Systems

Subtopic: Computer Hardware

Article Type: Computer Terms & Definitions

Difficulty: Medium

Difficulty Level: 4/10

CONTENTS

Properties
Types Of SD Cards
Advantages and Disadvantages Of SD Cards
History

Learn about what an SD card is in this article.

Stands for Secure Digital card. An SD card is a tiny, portable flash memory card used to store or transfer data between computers and other digital devices, like digital cameras, video recorders, smartphones, car navigation systems, music players, and PDAs. Since SD cards are removable, they can be inserted and removed from a compatible device.

Note:

The word 'secure' in 'Secure Digital' refers to its built-in DRM protection technology.

Properties

An SD card is about the size of a postage stamp and weighs around 2 grams. Every SD card has a slanted corner to ensure that the card can only be inserted in one way. To prevent the card from being written to (read-only), the left side of the card has a physical slider when moved to the LOCK position.

An SD card is similar in size to an MMC (Multimedia Card), but smaller than older memory card types, like a SmartMedia card or CompactFlash card.

Types Of SD Cards

The versions of SD cards with their physical dimensions and storage capacity are shown below.

Standard SD - 32 mm x 24 mm x 2.1 mm.
MiniSD - 21.5mm x 20mm x 1.4mm.
MicroSD - 15mm x 11mm x 1.0mm.
SD Standard Capacity - Storage capacity ranges from 128 MB to 2 GB and supports speeds of up to 12.5 MB/s. The default format for these cards is FAT16 (File Association Table.)
SD High Capacity (SDHC) - Storage capacity ranges from 4 GB to 32 GB and supports speeds of up to 25 MB/s. The default format for these cards is FAT32.
SD eXtended Capacity (SDXX) - Storage capacity ranges from 64 GB to 2 TB and supports speeds of up to 312 MB/s. The default format for these cards is exFAT.
SD Input Output (SDUC) - These SD cards combine input/output functions with data storage. They have a 128 TB storage capacity and support speeds of up to 985 MB/s.

Advantages and Disadvantages Of SD Cards

The advantages of SD cards are:

Like USB flash drives, they are extremely portable storage devices due to their small size and weight. This makes it easy to transfer data between multiple devices.
They have no moving parts. This makes them more durable as knocks and bumps are less likely to damage them.
Like CDs, DVDs, and USB flash drives, they don't require an internet connection to use. This makes it easier to use them whilst travelling and avoids expensive mobile data charges from mobile service providers.
Low power consumption - SD cards require little power and are a battery-supported storage device that can work well in a smartphone that consumes low power.

The disadvantages of SD cards are:

Compared to SSDs and HDDs, storage capacity is low. The average storage capacity of an SD card is around 64 GB. Although SD cards with a larger storage capacity are becoming more widely used, they quickly become very expensive.
Like USB flash drives, they can be easily lost due to their small size. For example, they can fall out of someone's pocket without them noticing, they could get lost in a large drawer, or they could fall down the back of a sofa.
There are quite a lot of enhancements and standards in SD cards, which can lead to compatibility problems with SD card readers.
They are fragile and prone to breaking. It doesn't take much for them to crack, twist, or bend, leading to an unreadable card. Once it is broken, the data will also become corrupt.

History

In 1999, SanDisk, Panasonic (Matsushita), and Toshiba agreed to develop and market the Secure Digital (SD) Memory Card. The card was the successor to the MultiMediaCard (MMC) and provided DRM based on the Secure Digital Music Initiative (SDMI) standard and a high memory capacity. It was designed to compete with the Memory Stick, a DRM product that Sony had released the year before.