What is the difference between SD Card and eMMC

 

SD Card:

SD Card stands for Secure Digital and is a NAND flash type memory. SD Card has an internal memory core and interface to an onboard controller. The on board controller interfaces externally to an SD interface. SD interface has Clock, command and data pins. SD cards are classified into various categories based on their physical size, speed and Memory size. Based on physical size they are classified as Full size SD card, mini SD  card and micro SD card. Based on storage, they are classified as SD, SDHX and SDXC. Based on speed they are classified into classes - class 2, class 4, class 6, class 10. SD card is used for data storage 

Below are the important SD card pins:

• CMD
• CLK
• GND
• DATA0-DATA3
• VCC

Electrical Design considerations for SD card:

• Pull-up resistors required for CMD, DATA signals
• Power to SD CARD to be controlled through MOSFET
• Use the loopback to detect the card insertion

eMMC Card:

eMMC stands for embedded Multimedia card and is a NAND flash type memory. eMMC is another flash type of memory used in mobiles and tablets. eMMC protocol is used to talk to eMMC. Where as the SD card can be removed, eMMC is soldered to PCB. As this is solderable to the PCB, this is internal memory and is fixed once board is made. eMMCs are available in BGA package. eMMC are available in Similar to SD card, eMMC also has internal controller interfaced to core memory. The controller interfaces to the external world. The advantage of internal flash controller that it eases some of the activities from main controller in the PCB. eMMC is an alternate to SSD but eMMCs are not available in higher sizes like the SSD. eMMC is mainly used for data storage. OS image is stored in the eMMC Cards. eMMC transfer speeds are up to 400 MB/s. The latest eMMC standard is eMMC 5.1A. 

Below are the important eMMC pins:

• CMD
• CLK
• GND
• DATA0-DATA7
• RESET 
• DATA STROBE
• VCC – Core supply (3.3V)
• VCCQ – I/O supply (1.8V – 3.3V)

Electrical Design considerations for eMMC card:

• Pull-up resistors required for CMD, DATA signals
• Power to SD CARD to be controlled through MOSFET
• Use the loopback to detect the card insertion