From an article I stumbled upon today, detailing the file manager that shipped on virtually every Symbian device in history.
The Files UI should be familiar to anyone that has used a file manager or folder system/explorer on a computer and it behaves the same as well. Pictured to the left is the standard view when you open Files. It shows several "drives", C:, E: and F: with F: being your memory card if your Symbian device has a memory card (SD, Mini/Micro SD) slot. Pictured to the right, you can see additional drives that are shown when you connect external devices via USB On-The-Go (if your device has USB-OTG) such as flash drives, hard drives or other phones. G: and H: represent the Mass Memory and Memory card on my Nokia N8 that is connected to my 808 PureView via USB OTG... that's a LOT of GBs to manage!
Back when I used Symbian as my main smartphone operating system (I had an E72), I always found it funny that Symbian used drive letters, while the mobile operating system I used for years and years (Windows Mobile/PocketPC) did not - or at least, not in a user-visible manner. At the time, I assumed that Symbian used drive letters in a virtual way to placate Windows users who were used to them.
In recent years, however, I've found out that Symbian's use of drive letters actually goes back much farther than that. Psion's EPOC (Symbian's 16bit predecessor; Symbian was created by Psion) also used drive letters - open up a Series 3 (I have a 3a) and you'll see that the two disk slots are designated A and B. Going even further back in time, even my Psion Organiser II (1986) used A: and B: for its two disk slots. I don't have a device to check, but I would assume that the Organiser I also used drive letters.
Interesting how a concept dating back to CP/CMS made it all the way to the most modern Symbian phones.