Dual-channel memory modules are two memory modules with the same specification, capacity and serial number in the same package.

Because a dual-channel memory is connected to the memory controller through a series of wires, it requires two sets of memory modules with the same capacity and electrical specification. Transfer speed increases as the memory bus capacity increases from 64 bit to 128 bit. Users must install the two modules in the specific DIMM slots to enable dual channel function to have a stable usage.

No, DDR4 memory modules can't be backward compatible with DDR3/DDR2/DDR1. Each module has different pin numbers and notch positions, so they can be installed in repective socket only. The power supply for each generation also varies:
DDR1 DIMMs voltage is 2.5V;
DDR2 DIMM voltage is 1.8V;
DDR3 DIMM voltage is 1.5V (or 1.35V for low-voltage version);
DDR4 DIMM voltage is 1.2V.

Please make sure the memory module is correctly oriented that the notch of the module matches the memory slot, and then gently push the module straight down to the slot.

  *Be aware that you must turn the computer off before installing or removing the modules.

Reasons causing memory card read failure are as follows:

1.  Power of camera is switched OFF while the camera is accessing data.
2.  Taking a picture when the battery is low.
3.  Withdrawing the memory card when the camera is accessing data.

The remedy to the above problems is to avoid incorrect use of the memory card. If unfortunately any of the above
happens, use PC and a card reader to re-format the memory card.

There are two main reasons for data corruption in a memory card.
1. Taking pictures or recording with a camera that is running low on batteries, or has an unstable power supply.
2. Removing the memory card from a device during a read/write operation. Please make sure that you have safely ejected your memory card before unplugging it from your device.

* Please format your memory card in the camera before using.

The majority of digital cameras only support the FAT format; if you have formatted the memory card in another format (NTFS or FAT32), your camera may fail to recognize the card. You will have to re-format the card by selecting the FAT format.

It is recommended to format a memory card before using it. For using on a cell phone or a camera, it is recommended to
format the card with the cell phone or camera intended to use the card since formatting with the intended device will
have preset directories created onto the card. In the case of formatting a memory card with a PC but using it on a
camera or cell phone, the device may have problems recognizing and utilizing the card.

1. Checking the compatibility of mobile phone the memory. 
Please check the specifications of your mobile phone and make sure the memory card is compatible with your mobile. Some mobile phone support less than 32GB memory card, and 64GB card can't work on it.

2. Formatting file system. With 64GB memory card supported the default format file system is exFAT and it may not work with the cards be formatted by FAT32. And you need to re-format the card on your mobile phone again.

3. The memory card might broke down. Please go back to the place you bought the card and check about the after service issues.

The size limit of an FAT32 single file is 4GB, therefore a movie exceeding 4GB cannot be stored. You may format your USB disk with NTFS format to enable storing single files that exceed 4GB.