The Lenovo ThinkPad Edge E-540, which I recently chose as my new laptop, is available in various hardware configurations. There are not only different CPU/GPU/memory options, but also the storage subsystem can somewhat vary. Nevertheless, the usual configurations available at big resellers (like Amazon, NewEgg etc.) come with either 1 TB 5400 rpm or 500 GB 7200 rpm rotational regular drive, coupled with an optional 16 GB SSD cache module.
There are multiple options to get a bigger SSD for the notebook, each having its advantages and disadvantages. The article describes a procedure to replace the original 16 GB SSD module by a bigger one, and use it as a boot drive with the system instead of cache. This way the big original HDD can stay in the machine, while still having the option to boot from the system from SSD.