There’s no specific definition of a supercomputer: it’s more of a comparative term that refers to the most powerful computers available at any particular time. Indeed, many machines previously dubbed supercomputers would be considered pretty standard machines today.
The CX1 is produced by Cray, a firm which is largely seen as the pioneer of supercomputers. To show how far computing has come, the first Cray supercomputer had just 8MB of memory, whereas even the cheapest home PCs today will come with at least 512MB.
The CX1, which runs up to 16 different processors, can work with as much as 512GB (not MB!) of memory, and store up to 4,000GB of data.