Generally ECC memory RAM is slightly slower than non-ECC RAM because it has to perform additional automatic error-checking and correction functions.This memory is usually used in server for reliability & mission critical application minimizing the risk of crashes or data corruption during the data transfer which a server has a much higher load and fault tolerance . And price is much higher compared to non-ECC memory. (ECC/ Buffered memory).
As the abbreviations stands for error correcting code(ECC memory) known for their quality construction and compatability. Even though most modern platforms support it, you must make sure that the specific processor and motherboard combination works with ECC memory. In the server world, where ECC memory is commonly used and by default. With ECC memory modules being more expensive than non-ECC modules due to the added functionality (Non ECC/ Unbuffered memory)
To know if your desktop PC/ or laptop supports an ECC Ram or Non-ECC visit the motherboard manufacturers website. As for the physical appeareances both types of RAM modules generally share the same factors such as DIMM (Dual inline memory module) or S0-DIMM (small outline DIMM) some similar appearance & size.