• Is a general purpose device
• that can read, process and write numbers
  • (and things that can be represented by numbers)
• to and from the memory
• following a program stored also in the memory
  • many simple steps
• Changing the program changes the purpose of the machine

Since old times physical tools are called hardware

That includes al the physical parts of the computer (what you can kick)

Programs determine the function of the computer, but they are not “physical”.

That is software (what you can only insult)

• Its contents disappear if the power is turned off
• and all this currently active information is lost

That’s why it’s prudent to save your work often

Electric problems can be a real disaster

You can think of the RAM as

• a large collection of identical little boxes
• numbered from 1 up to 1000000000
• each box can hold a small amount of information.

Capacity is measured in bytes

What is the capacity of your computer?

For technical reasons modern computers handle memory in bytes

• memory big enough to hold a single character
  • like W or @
• Or a small integer number (0 to 255)

Numbers with decimals can be represented using scientific notation \[1.8466 \cdot 10^{19}\]

In the computer we write 1.8466E19

• Inf: Positive Infinity, 1/0
• -Inf: Negative Infinity, -1/0
• NaN: Not a number, 0/0
• NA: Not Available, missing data

We have a fixed number of digits

Not all numbers are represented exactly

For example \[\frac{1}{3}=0.33333333\cdots\] cannot not be represented exactly with 10 digits

• Sound is transformed into electricity by a microphone.
• The voltage is measured 44100 times each second
• Each sample is stored as a number in a CD

Two steps: sampling (in time) and discretization (in voltage)

When they don’t have energy, they forget all

All data must be stored in secondary memory

Today secondary memory is

• hard disk
• USB stick
• Cloud storage

Besides the data itself, files have metadata

That is, data about the data. For example

• Files have a name
• Files have a modification date, maybe other dates too
• Files have a size
• Files have permissions

The names of the files are “words”: a series of letters, numbers and some symbols

Technically, a filenames is a String or list of characters

Maximum length of a filename is 250 characters

Avoid /, :, +, |, <, *, >, " and '

Use letters (A-Z, a-z), numbers (0-9), ., -,   and _

In some systems small caps and BIG CAPS are not equivalent. Be systematic and coherent

If the filename includes ., the text after it is called extension

In Microsoft Windows (c) extensions are usually 3 letters

• EXE, JPG, DOC, XLS, TXT, CSV
• These are hints on how to interpret the file

At low level there is only one type of file

For us, it is useful to separate in two:

Text Files

each byte is a character, we can read it

Binary Files

bytes are grouped in binary numbers, representing images, sounds, etc.

Among binary files we have EXE files, which are programs for Windows

At low level there is only one type of file

For us, it is useful to separate in two:

Text Files:

each byte is a character, we can read it

Binary Files:

bytes are grouped in binary numbers, representing images, sounds, etc.

Among binary files we have EXE files, which are programs for Windows

• are universal
• are easy to read and write from a program
• do not have any style like bold or italic
• are like books without figures

Microsoft Word files (doc or docx) are NOT text files

• Binary files are hard to read
  • unless you have the correct program
• Text files can be read by humans
  • Each byte is a letter
• Text files can be read by computers
  • Data must be recyclable
  • The output of one program is the input of another program

To many people, computers are not helping. Instead they feel like computers make things harder.

The same happened when electric engines were invented

• Structured documents
• Markdown
• RStudio

Google them. Be prepared