How Computers Think and Store Information

Computers follow instructions and store typed values. Excel cells are memory you can see.

This week

Week 1 · Excel Ch. 1 · Excel Project 1. Next: data literacy (lecture 2).

Objectives

After this lecture you should be able to
  • Explain, in plain language, what a computer does with input, instructions, memory, and output
  • Distinguish a value from a display format (the same idea in RAM and in an Excel cell)
  • Recognize common data types you will meet all semester: numbers, text, dates, and true/false
  • Create a simple Excel workbook, save it to OneDrive, and inspect what is actually stored in a cell

Computers do not think

A useful myth to retire
  • Everyday speech: “the computer thinks”, “Excel calculated that”, “my phone knows”
  • More accurate: a computer follows instructions on data
  • Those instructions were written by people (or by other programs written by people)
  • Excel is one such program: you write many of the instructions as formulas
The loop every computer runs 
flowchart LR
  A[Input] --> B[Instructions]
  B --> C[Memory]
  C --> D[Output]
  D --> C
  • Input: keyboard, file, sensor, a cell you typed into
  • Instructions: a program, a formula, a Python script, a Copilot prompt that becomes code
  • Memory: short-term (RAM / unsaved workbook) and long-term (disk / OneDrive / .xlsx file)
  • Output: screen, chart, printed report, another file
Why this belongs in an Excel course
  • A formula is a tiny program living in a cell
  • A cell is a named memory location (B2, Grade, Total)
  • If you do not know what is stored versus what is shown, later charts and pivots will lie politely

Instructions, memory, and files

Hardware, very briefly
  • CPU: executes instructions, one after another (very fast, not magic)
  • RAM: working memory; disappears when the machine (or the unsaved file) goes away
  • Storage: SSD, USB drive, OneDrive; survives after you close Excel
  • Operating system: the program that shares the machine among Excel, the browser, and everything else
Files are containers, not the data itself
  • A .xlsx workbook is a file: a packaged collection of worksheets, charts, and metadata
  • Closing Excel without saving is throwing away RAM, not the last version on disk
  • AutoSave (OneDrive / SharePoint) is persistence happening in the background
  • Same idea in Word (.docx) and PowerPoint (.pptx): the file is the long-term copy
Bits and bytes, only as far as we need
  • Computers store everything as bits (0 and 1)
  • A byte is 8 bits; enough for a small integer or one character in older encodings
  • You will not count bits in this course
  • You will care that the machine must be told whether a pile of bits is a number, text, or a date

Workbook anatomy

Excel Ch. 1 — the objects you will click all semester
  • Workbook: the .xlsx file (the container)
  • Worksheet: one grid inside the workbook (Sheet1, Data, Notes)
  • Cell: intersection of a column letter and a row number (B2)
  • Range: a rectangle of cells (B2:D10)
  • Formula bar: shows the stored instruction or value
  • Ribbon: Home / Insert / Data / Formulas — where most lab steps live
  • Name Box: left of the formula bar; jump to a cell or name a range
Good first habits
  • Rename sheets (Data, Notes, Checks) instead of leaving Sheet1
  • Freeze the header row when the list grows (View → Freeze Panes)
  • Save to OneDrive so AutoSave is persistence, not a hope
  • One idea per sheet when you can: raw data stays raw

Types of information

Why types exist
  • 100 the number and "100" the text are not the same
  • You can add numbers; you cannot (sensibly) add two ZIP codes stored as text
  • Dates are not “how they look”: they are values that can be sorted and subtracted
  • True/false (Boolean) values drive IF decisions later in the semester
Types you will use constantly in Excel
What you mean Typical Excel storage Danger if you get it wrong
Quantity, money, score Number Text that looks like a number will not SUM
Name, ID, ZIP, phone Text Leading zeros vanish if stored as Number (08052 → 8052)
When something happened Date/time (a serial number) Sorting “September” as text puts it after “August” incorrectly
Yes / no, pass / fail Boolean or TRUE/FALSE "TRUE" as text is not the same as TRUE
A rule, not a value Formula Copy-paste as values and the rule is gone
Office parallel: Word and PowerPoint also store typed stuff
  • Word: a heading is not just big bold text; it is a style the document model understands
  • PowerPoint: a chart pasted as a picture cannot be updated when the Excel data changes
  • Theme of the course: structure first, decoration second

What Excel is really storing

Look at the formula bar, not only the cell
  • The cell display is a costume
  • The formula bar is closer to memory
  • Example: cell shows 50%; formula bar may show 0.5
  • Example: cell shows 9/1/2026; Excel may be storing 45901 (a date serial)
Number formats are costumes
  • General, Number, Currency, Percentage, Date, Text change how a value looks
  • Changing the format does not change the underlying value (usually)
  • Exception: if you type into a cell already formatted as Text, Excel may store digits as text
  • Green triangles and ISTEXT / ISNUMBER are early debugging tools
Formulas are instructions stored in cells
  • =B2+C2 means: when asked, fetch B2 and C2, add, put the result here
  • Recalculation is the computer running that instruction again
  • If B2 is text "10", the instruction may fail or silently do the wrong thing
  • This is SLO4 and SLO5 in miniature: right types, then check correctness

Try this in Excel

Lab 1 — Build a tiny memory map
  1. Create a new workbook and save it to OneDrive as week01-memory.xlsx
  2. In A1:A4 enter labels: Quantity, ZIP, Date, Share
  3. In B1 enter 12 (Number)
  4. In B2 enter 08052 and format the cell as Text before or immediately after typing; confirm the leading zero stays
  5. In B3 enter today’s date; change the format between Short Date and Number; watch the serial
  6. In B4 enter 0.25 and format as Percentage
  7. In C1 enter =B1*B4 and explain in a Word comment or adjacent cell what instruction you wrote
Lab 1b — Persistence
  • Close the file, reopen it: RAM was discarded; the file restored the cells
  • Turn AutoSave off temporarily (if you can), type a value, force-quit Excel: that value was only in RAM
  • (Do this on a throwaway copy.)
Discussion
  • Designate one note-taker
  • Where have you seen a computer “get the type wrong” in real life (grades, money, IDs, dates)?
  • If Copilot writes =B2+C2 for you, what would you inspect before trusting the total?

Takeaways

Carry these into next week
  • Computers follow instructions; Excel formulas are instructions
  • Storage has types; display formats can hide those types
  • A workbook file is persistence; an unsaved grid is not
  • Next lecture: before writing formulas, decide what a row and a column mean
Placeholder notes for expansion
  • Screenshot walkthrough of Format Cells vs formula bar
  • Binary/place-value optional appendix for curious students
  • Short Word activity: styles vs manual formatting, same “type vs appearance” idea