The Lenovo E550 has an HDD storage medium which is better than the SSD storage medium found on most similar spec portable PCs that have been on the market for around the same time as it. HDD is a traditional storage drive which stores the information on magnetic disks. HDD drives are slower than other forms of storage such as solid state drives (SSD) and flash drives.
An HDD storage medium is in fact the worst storage medium amongst all notebook PCs of a comparable age and spec to the E550.
The best storage medium across comparable types of laptop is SSD.