Can a computer run without hardware?
Yes, It May Sound Little Awkward but it can run without
hardware. A computer does not need to be electronic, nor even have
a processor, nor RAM, nor even a hard disk. While popular usage of
the word "computer" is synonymous with a personal electronic
computer, the modern definition of a computer is literally "A
device that computes, especially a programmable [usually]
electronic machine that performs high speed mathematical or logical
operations or that assembles, stores, correlates, or otherwise
processes information". Any device which processes information
qualifies as a computer, especially if the processing is
purposeful. Historically, computers evolved from mechanical
computers and eventually from vacuum tubes to transistors. However,
conceptually computational systems as flexible as a personal
computer can be built out of almost anything. For example, a
computer can be made out of billiard balls (billiard ball
computer); an oft-quoted example. More realistically, modern
computers are made out of transistors made of photo lithographed
semiconductors.
There is active research to make computers out of many promising
new types of technology, such as optical computers, DNA computers,
neural computers, and quantum computers. Most computers are
universal, and are able to calculate any computable function, and
are limited only by their memory capacity and operating speed.
However different designs of computers can give very different
performance for particular problems; for example quantum computers
can potentially break some modern encryption algorithms (by quantum
factoring) very quickly.