85 lines
4.3 KiB
Markdown
85 lines
4.3 KiB
Markdown
---
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tags:
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- theory-of-computation
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---
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# Defining a computer
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> A general-purpose computer is one that, given the appropriate instructions and
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> required time, should be able to perform most common computing tasks.
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This sets a general purpose computer aside from a special-purpose computer, like
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the one you might find in your dishwasher which may have its instructions
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hardwired or coded into the machine. Special purpose computers only perform a
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single set of tasks according to prewritten instructions. We’ll take the term
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_computer_ to mean general purpose computer.
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Simplified model of what a computer is:
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Although the input, output and storage parts of a computer are very important,
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they will not be the focus of this course. Instead we are going to learn all
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about the process part, which will focus on how the computer is able to follow
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instructions to make calculations.
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## **Supplementary Resources**
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### Early computing (_Crash Course Computer Science)_
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[Early Computing: Crash Course Computer Science #1](watch?v=O5nskjZ_GoI)
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- The abacus was created because the scale of society had become greater than
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what a single person could create and manipulate in their mind.
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- Eg thousands of people in a village and tens of thousands of cattle
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- In a basic abacus each row of beads (say its coloured) represents a different
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power of ten
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- As well as aiding calculation, the abacus acts as a primitive storage device
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- Similar early computing devices: astrolabe, slide rule, sunrise clocks, tide
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clocks
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> As each increase in knowledge, as well as on the contrivance of every new
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> tool, human labour becomes abridged. **Charles Babbage**
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- One of the first computers of the modern era was the Step Reckoner built by
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Leibniz in 1694.
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- In addition to adding, this machine was able to multiply and divide
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basically through hacks because from a mechanical point of view,
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multiplications and divisions are just many additions and subtractions
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- For example, to divide 17/5, we just subtract 5, then 5, then 5 again until
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we can't do anymore hence two left over
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- But as these machines were expensive and slow, people used pre-computed tables
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in book form generated by human computers. Useful particularly for things like
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square roots.
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- Similarly range tables were created that aided the military in calculating
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distances for gunboat artillery which factored in contextual factors like
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wind, drift, slope and elevation. These were used well into WW2 but they were
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limited to the particular type of cannon or shell
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> Before the invention of actual computers, 'computer' was a job-title denoting
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> people who were employed to conduct complex calculations, sometimes with the
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> aid of machinery, but most often not. This persisted until the late 18th
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> century when the word changed to include devices like adding machines.
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- Babbage sought to overcome this by designing the **Difference Engine** which
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was able to compute polynomials. Complex mathematical expressions that have
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constants, variables and exponent. He failed to complete it in his lifetime
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because of the complexity and number of intricate parts required. His model
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was eventually successfully created in the 90s using his designs and it
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worked.
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- But while he was coming up with this he also conceived of a better and
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general purpose computing device that wasn't limited to polynomial
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calculations → the Analytical Engine.
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- It could run operations in sequence and had memory and a primitive printer.
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It was way ahead of its time and was never completed.
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- Ada Lovelace wrote hypothetical programs for the Analytical Engine, hence
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she is considered the world's first computer programmer.
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- At this point then, computing was limited to scientific and engineering
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disciplines but in 1890, the US govt needed a computer in order to comply with
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the constitutional stipulation to have a census every ten years. This was
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getting increasingly difficult with the growing population - it would take
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more than 13 years to complete. This led to punch cards designed by Herman
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Hollereth. From this IBM was born
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