How Computers Work

Which House will the Apple be in … ?

By the end of today, you will:

Understand the different parts of a computer and how they interact
Navigate through your computer using the command line
Create and delete folders and files

The worst prediction in history?

The world will need no more than “about five computers”

Thomas Watson, IBM Corporation, 1940s

Source

A computer is an INFORMATION PROCESSOR

Computers take in information or data (INPUT),

crunch it (PROCESSING),

spit out the results (OUTPUT),

and store the data and/or the result (MEMORY).

Your microwave oven is a very simple computer

INPUT: numbered keypad

PROCESSING: convert key presses to cooking time and temperature

MEMORY: clock

OUTPUT: e.g., Cook for 3 minutes at high temperature … DINNER!

$59.99 from Target

Output …

Mmm.. dinner

Your laptop is a more complex computer

INPUT: keyboard, mouse, scanner, …

PROCESSING & MEMORY: central processing unit (CPU) interprets and executes program instructions, and communicates with input, output, and secondary storage. It has a small amount of temporary memory.

OUTPUT: screen, printer, video, …

SECONDARY STORAGE: hard drives, external drives, flash. These can store large amounts of data and software

HARDWARE is the physical computer and peripherals

Bits of a computer …

SOFTWARE tells the computer what to do

Planned, step-by-step instructions.

Two kinds of software:

System software: Operating system (e.g., Windows, MacOS, Unix)
Applications software: Word, Excel, unix programs, .. R!

An operating system versus permanent physical circuits

Operating systems …

do a variety of DIFFERENT things;
INTERACT with the user in COMPLEX ways;
can CHANGE what it does and how it interacts

The operating system is an intermediary between applications and hardware

It manages the computers resources (CPU, memory, drives, outputs)
Establishes a user interface (graphical or command-line)
Executes and provides services for applications software.

User Interfaces allow humans to interact easily with computers

You are probably mostly familiar with GRAPHICAL USER interfaces (GUI, “goo-ee”).

GUIs allow users to interact with mouse/finger movements and clicks.

R uses a COMMAND-LINE interface (CLI).

CLI are less user-friendly at first, but much more powerful:

Can keep permanent record of commands
Can automate some/many/all steps by calling this record

All personal computers have GUI and CLI access!

An Application Programming Interface (API) allows software to interact easily

Analagous to a GUI, but for software ‘users’.

Usually an abstraction of underlying specific instructions.

Allows software to work on many/all operating systems.

More here.

File systems and directory structure

A file system allows us to access specific data/information on a computer.

Naming is derived from office filing systems for paper documents.

“FILE” = a group of data, e.g., a Word document, R code, image, …

“FOLDER” (or DIRECTORY) = a collection or group of files.

Can be HIERARCHICAL, i.e., allow subfolders.

“PATH” = Full location of a (sub)directory: e.g., “C:\Simon\Teaching\FES720"

Path: The address of a folder or file

It is hierarchical like a postal address:

Simon Queenborough
301 Prospect St
New Haven
CT
USA

“PATH” = Full location of a (sub)directory:

"C:\Simon\Teaching\FES720\"

or file

"C:\Simon\Teaching\FES720\myRfile.txt"

Path can be absolute or relative

The PATH can be absolute (i.e., it includes the ‘country’ and ‘state’):

"C:\Simon\Teaching\FES720\"

Or, relative to your working directory.

If your working directory is ‘Teaching/’:

"FES720\"

Note: Working with relative paths allows your code to transfer between different computers and users much more easily (we will come back to this).

PATHS: shortcuts

Relative paths can also be specified using shortcut codes.

So, if the working directoy = C:\Simon\Teaching\FES720\

Path = “.” indicates the current working directory

Path = “.” = C:\Simon\Teaching\FES720\

Path = “..” indicates the directory one level above the current working directory

Path = “..” = C:\Simon\Teaching\

Use paths to move files around in your code

Let’s assume we have the following hierarchical directory stucture:

─ R-project-1
  |   └─ analysis.r
  ├─ raw_data
  |   ├─ 2015
  |   ├─ 2016
  |   └─ 2017
  ├─ processed_data
  |   └─ data_all_yrs.csv
  ├─ results
  └─ figures
      └─ plot1.png

Use paths to move files around in your code

─ R-project-1
  |   └─ analysis.r
  ├─ raw_data
  |   ├─ 2015
  |   ├─ 2016
  |   └─ 2017
  ├─ processed_data
  |   └─ data_all_yrs.csv
  ├─ results
  └─ figures
      └─ plot1.png

Suppose we want to:

read data from raw_data/2015/ and raw_data/2016/,
process it and write the file to processed_data/,
read that file in, run an analysis and make a figure to save into figures/

Two ways to move around:

bad: use setwd() a lot
good: use relative paths from the main directory (R-project-1/) to read and write

File names

Uniquely identifies a file.

Different OS have different naming conventions and allowed characters.

DRIVE: C:

USER or ROOT: Simon

DIRECTORY: Teaching

SUBDIRECTORY: FES720

FILENAME: myRfile

FILE EXTENSION: .txt

File and path names are TEXT

# You will use this function in the lesson
getwd()

# Notice the speech marks/quotation marks:
"C:\Simon\Teaching\FES720\"

File systems in Mac, Windows, and Linux

R can run in all three OSs, but there are minor differences.

Backslash (\, windows) vs slash (Mac, Linux)

https://www.howtogeek.com/181774/why-windows-uses-backslashes-and-everything-else-uses-forward-slashes/

File encodings (non-ASCII text, e.g., text with accents, apostrophes, etc.)

https://en.wikipedia.org/wiki/Text_file

Line endings (newline, return+newline)

https://en.wikipedia.org/wiki/Newline

File utilities allow you to manage the file system

In a GUI, you can create, delete, rename, move, copy, change metadata, etc. files and folders.

You can do the same in a CLI.

File utilities from the CLI allow:

automation of data cleaning and processing,
- e.g, read in various data files from multiple (sequential?) years, process, and write to new file/s.
creation and removal of temporary folders and files to store intermediate or temporary steps
- e.g., in file encoding and unencoding

How Computers Work

By the end of today, you will:

The worst prediction in history?

A computer is an INFORMATION PROCESSOR

Your microwave oven is a very simple computer

Output …

Your laptop is a more complex computer

HARDWARE is the physical computer and peripherals

SOFTWARE tells the computer what to do

An operating system versus permanent physical circuits

The operating system is an intermediary between applications and hardware

User Interfaces allow humans to interact easily with computers

R uses a COMMAND-LINE interface (CLI).

An Application Programming Interface (API) allows software to interact easily

File systems and directory structure

Path: The address of a folder or file

Path can be absolute or relative

PATHS: shortcuts

Use paths to move files around in your code

Use paths to move files around in your code

File names

File and path names are TEXT

File systems in Mac, Windows, and Linux

File utilities allow you to manage the file system

File utilities from the CLI allow:

Further Reading