A solid state disk, or disc, (hereafter SSD) refers to computer primary storage that has no moving parts. Whereas traditional forms of primary storage were rust-covered Frisbees, brown donuts or long strands of magnetized Christmas Tree trimmings, an SSD is comprised wholly of Flash Memory*.
SSDs are a huge advancement in computer technology in that they have become one of the best ways to wrest cash from the pockets of customers who would otherwise be completely happy with their computer if they didn't have another acronym to buy.
This is because:
Flash memory is FAST. SSDs write data and read data faster than traditional rotational media ever could. This also means that there is another open arms race for "faster". Whereas before, your standard hard drive may have been seen as current for any number of years, an SSD becomes second-hand thrift store fodder mere weeks after being announced.
Flash memory wears out. A section of Flash Memory is built from a series of "cells", each cell containing one bit (although some technologies now allow more bits per cell, depending on local Penal Occupancy Codes). When the bit value in the cell is to read, the microscopic gnome that lives in the cell reads his current value from his notepad and screams it down the hall to the rest of the computer. This is fine and to be expected.
But when a "write" is signaled and the stored value needs to change, that's where the problems start. When the gnome gets word that his value has changed, usually via a note flushed through the toilet system (referred to as "the Bus"), he flips to a new page in his notepad and writes down the new value. But he only has a limited number of pages so eventually he is back at the first page that was already used. He then needs to erase that value and write in the new one. But since prison-issue paper is so poor he can only do this erase-rewrite cycle a limited number of times until all his pages are ruined and he can't store any more values.
This means that, as a whole, an SSD will eventually die. Whereas a standard Spinner has an MTBF (Minimum Time Before a Fuckup) of several years, an average SSD has an MTBF of between 1- and 1-quintillion seconds -- depending on how much porn you download.
This also means that manufacturers of SSDs (who are then, by course, imprisoners of innocent microscopic gnomes) have a built-in revenue model. Your SSD WILL FAIL ONE DAY, and you will accept this as normal and buy another!
SSDs are currently small in capacity. The process by which the gnomes and their cells are made smaller is currently able to shrink each of them down to a measurement of about 28nm (where 'nm' means, of course, "gNome Microfeet"). There are very impressive maths involved to tell you how much data can be stored in what size, but suffice it to say that SSDs currently cannot store the same amount of data in the same physical space as a Rotational Hard Drive for the same cost. So you need to pay MORE MONEY for the SAME AMOUNT OF GNOME NOTEPADS.
Base Cost: Owing to all the gnomes, their shrinking, the notepads and graft to the Bureau of Prisons to look the other way, making SSDs is very expensive. So much so that when the manufacturers plug in an extra 200% profit margin to the cost of the device no one seems to complain. After all, complaining about how much things cost is so New Money.
SSDs are the future, though, no doubt. Couple their profit potential with the relentless upgrade cycle and multiply that by the square-hectares of pornography added to the internet every second, it is the perfect device for the perfect industry in the perfect country.
GOD BLESS NORTH AMERISTANIA.
*: there are some devices called "SSD" that use static RAM, linear RAM or winter rams, but they are outside of the scope here. Typically SSD refers to usage of Flash Memory.