What is code?

What is code?

Code is a way for humans to communicate with computers in order to produce a result.^*

* I made this definition up. Literally everything in this lecture is contestable, which we'll talk about more as we continue.

What is a computer?

To answer that question we'll look at the history of computing.

The history of computing is a huge topic. I'm streamlining this history based on what I think is relevant to a class about code. Check the class site for a slew of links and book suggestions if you want more history, and more discussion of how the history of computing is complicated and problematic.

On that note, remember that everything in this lecture is contestable. I've done my best to make sure this is all factually correct where possible.

Here we go.

Later interpretation of machine breaking (1812), showing two men superimposed on an 1844 engraving from the Penny magazine which shows a post 1820s Jacquard loom.

The Analytical Engine incorporated an arithmetic logic unit, control flow in the form of conditional branching and loops, and integrated memory, making it the first design for a general-purpose computer that could be described in modern terms as Turing-complete.

Ada Lovelace - 1833

Ada Lovelace - 1833

Ada Lovelace - 1833

The operating mechanism can even be thrown into action independently of any object to operate upon (although of course no result could then be developed). Again, it might act upon other things besides number, were objects found whose mutual fundamental relations could be expressed by those of the abstract science of operations, and which should be also susceptible of adaptations to the action of the operating notation and mechanism of the engine. Supposing, for instance, that the fundamental relations of pitched sounds in the science of harmony and of musical composition were susceptible of such expression and adaptations, the engine might compose elaborate and scientific pieces of music of any degree of complexity or extent.

Allan Turing proposes the idea of a Turing machine

PowerPoint is Turing Complete

For more on this, read PROGRAMMING THE ENIAC: AN EXAMPLE OF WHY COMPUTER HISTORY IS HARD By Leonard J. Shustek

Although it looks meaningless to most humans, this pattern of ones and zeros contains all of the commands and data required to complete the task. For example, when the microprocessor encounters the bit pattern: 00000011 11000011, it interpreters it as a command to take the 16 bits stored in the BX register, add them in binary to the 16 bits stored in the AX register, and store the result in the AX register. This level of programming is called machine code, and is only a hair above working with the actual electronic circuits.

Since working in binary will eventually drive even the most patient engineer crazy, these patterns of ones and zeros are assigned names according to the function they perform. This level of programming is called assembly, and an example is shown in Table 4-4. Although an assembly program is much easier to understand, it is fundamentally the same as programming in machine code, since there is a one-to-one correspondence between the program commands and the action taken in the microprocessor.

Kathleen Booth is usually credited as inventing/developing assembly language while working on ARC at Birkbeck College.

Direct precursor of COBOL

Grace Hopper