<span>In general you want to use the cheapest storage medium who's speed is compatible with the function it needs to perform. For active storage that's handled while running programs, you need memory whose speed is closely matched to the processor speed. And that would be the rather expensive semiconductor memory which is close to ideal for the task. But semiconductor memory has the disadvantage of being expensive and it loses the values stored when power is lost. So slower, persistent storage is used such as SSD (Solid State Drives) and hard disks. That media is cheaper, but slower, but still fast enough to handle tasks such as loading programs and data into memory for execution, or storing data generated by programs to persistent storage. But as with all man made things, disasters happen. Computers break down, hard disks crash, floods and fires happen, etc., and as a result data is lost. So we make backups. Backups have to have a lot of storage and they have to be cheap. But they don't need rapid access, you can start at the beginning and read (or write) all the way to the end. And for that purpose, magnetic tape is ideal. Magnetic tape is actually quite fast when you're simply streaming a continuous stream of data without any need to randomly access any piece of that data. And it's cheap, so you're willing to make a back up copy of your system and store that backup off site so a single disaster won't destroy both the primary system and the backup.</span>
C. system software
if it means drivers and so on
The purpose of the conclusion paragraph is not only to wrap up the essay, but also to show the strong and central points in the essay alone. Since you are wrapping up the essay, it's your final paragraph and you have to clearly state all of your points and what and why the essay is written (depends on what you are talking about). But, the one purpose of an essay's conclusion is to clearly state the central points of the essay.
