SD card

SD card Overview

Secure Digital (SD) memory card is based upon flash technology. The format of SD cards is similar to those of multimedia cards with slightly thicker in size. SD cards are available in the data transfer rates ranging 6x (900 KB / s) to 66x (10 MB / s). Higher end cards offer 133x and even higher speeds. So far SD cards are available in a wide range of capacities. These include 1, 2, 4, 6, 8, GBs, and 8, 16, 32, 64, 128, 256, and 512 MBs.

SD card Interfaces

Standard SD cards are thicker and cannot be inserted in MMC slots. But SD card slots support multimedia cards. SD slots allow connecting miniSD and microSD cards via physical interface adapter. SD cards with USB connectors also available. SD card readers allow access through various ports including USB, FireWire, and parallel ports. Furthermore SD cards are also accessed through floppy drive using a Flashpath adapter. <2>SD Card Transfer Modes SD cards operate in three data transfer modes. One is SD-SPI mode that offers separate serial in and serial out data transfer. Second is one-bit SD mode that offers a separate transfer format with separate command and data channels. Third is four-bit SD mode that offers four-bit parallel transfer. High-speed SD cards offer maximum of 100 mega bits / second transfer rate in four-bit SD mode. Also they work with first and second mode at the data rate up to 25 mega bits / second. Low speed SD cards support SPI and one-bit SD modes to offer data rates up to 400 kilo bits per second.

SD card Security Features

Secure digital cards are named as secure to protect music piracy. Multimedia cards did not offer any music piracy. So to overcome this deficiency SD cards were developed with DRM (digital rights management) technology. This scheme is the same as magic gates in memory sticks. But DRM is rarely used because it doesn't work much efficiently. For example SD cards accessed through card readers can be copied without any copyright protection. Moreover SD cards contain a write protect switch that can turn an SD card into read only mode.

SD card applications and uses

Secure Digital (SD) Cards serve as storage media in several devices especially portable devices. These include PDAs (personal digital assistants), digital cameras, mobile phones, handheld PCs, camcorders, and digital audio players. Secure digital (SD) slots also support various devices designed for SD form factors. Devices containing SDIO (secure digital input output) ports can use such devices. Some of these include Ethernet adapters, GPS receivers, modems, Wi-Fi adapters, Bluetooth adapters, IrDA adapters, RFID tuners, FM radio tuners, and barcode readers.

SD card and Other standards

The biggest competitor of SD cards is Toshiba's Smart Media card in digital camera. By now 50% of the digital camera market use Smart Media card and 40% uses SD cards.