"The Radxa E24C is a cheaper, lower-performance model that features a Rockchip RK3528A quad-core processor and support for up to 8GB of RAM, while the Radxa E54C looks nearly identical, but comes with up to 32GB of RAM and has much faster Rockchip RK3582 hexa-core chip. Prices start at $35 for the E24C and $55 for the E54.
Both boards feature aluminum cases for passive heat dissipation, but you can also add a fan if you want active cooling. Both support an optional eMMC module for onboard storage, and both also have M.2 2280 connectors for an optional PCIe 2.1 NVMe SSD or other add-ons, as well as a microSD card reader."
Source: Liliputing