A couple of readers recently sent a message to my Facebook page asking the  usage of dual Memory card Slot Dslr Cameras. Most of the professional cameras have dual memory card slots, one as Compact flash and other as SD card. Some dslr cameras have dual SD slots as well, but they are used by very few people.

Single SD memory card slot dslr

Examples of dual memory card slot dslr cameras from Canon include:

Canon 1D Mark IV

Canon 1D Mark III

Canon 1D Mark II

Canon 5D mark III

Canon 7D Mark II
Examples of dual memory card slot dslr cameras from Nikon include:

Nikon D300S

Nikon D3S

Nikon D5

Nikon D800

Nikon D800E
Example of dual memory card slot dslr cameras from other manufacturers include:
Pentax 645D
Pentax K-1
Fuji X-T2
Panasonic GH5
Sony A9
Olympus E-M1II

The bigger question here is why do we need dual memory card slot dslr cameras and whats the advantage? Lets try to find the answer from a user perspective. Professional cameras have 2 memory card slots for a variety of purposes, although the ability to use both cards at same time varies from brand to brand. The major reasons can be broadly summarized into three categories:

Better Redundancy: Same image across multiple memory cards. This offers mirroring of same files, which in turn serves as back up. As a professional photographer, the worst scenario would be a failing memory card in the middle of a wedding. Professional photographers charge money, and clients expect them to be reliable no matter what happens. The camera writes twice in this scenario, as it has to mirror the same exact file. 

Different file format to different card: This can save a lot of buffer space and improve the speed by major gap. You can write RAW files to one memory card and JPEG files to the other. This saves a lot of time as it prevents double passing of data going through the camera every time. If speed if your top priority for a dual card slot camera, this method works wonders. 

Auto Switching: 

This category applies to users who are more relaxed about the redundancy and speed of capturing photographs. It basically means the camera switches to second card once the first card is filled.

Lastly, every manufacturer is coming up with unique ways to store different format data on multiple cards. Some Nikon dslrs allow users to write video to one memory card and photos to the other. Canon allows a user to use both compact flash type I and II cards in some dslr cameras. Also, the ability to use existing memory cards when upgrading bodies is another way to save some decent amount of money. Do you think the flexibility offered by dual memory card slot dslr cameras is worth the price?