How Computers & the Internet Work

SAP Implementation Consulting & ERP - Startupistan Germany · Block I · study notes for revision.

---

Hardware vs software

Every computer is two halves working together. Hardware is the physical body - the parts I can touch. Software is the instructions that tell the hardware what to do. Hardware with no software is a dead box; software with no hardware is an idea with nowhere to run. Neither is useful alone.

The parts that matter, and what each does

I don’t need every component by name - I need a few parts by what they do, and what breaks when there isn’t enough of each.

Part	Full name	Job	Symptom when short
CPU	Central Processing Unit	Does the actual work - thinking, calculating	”Slow computer” is usually a CPU story
RAM	Random Access Memory	Short-term working space for whatever is open right now	Too little → crawls; a “memory leak” quietly eats it up
Storage	SSD / hard drive	Keeps files, photos, programs when the power is off	”Storage full” → can’t save until you clear space
GPU	Graphics Processing Unit	Drawing graphics, video, games - and now training/running AI	Weak GPU → stuttering video, can’t run heavy games
I/O	Peripherals + ports	Screen, keyboard, mouse plug in via ports (USB the common one)	-

The desk analogy - and the one insight

RAM is the desk surface (what I spread out to work on now), storage is the filing cabinet (kept for later), the CPU is me, the worker. So: more RAM ≠ more storage. More RAM = do more at once without slowing. More storage = keep more things. Confusing the two is the classic beginner mistake - a slow machine usually wants RAM, not a bigger drive.

Same core idea scales across desktop, laptop, tablet, phone - each has a processor, memory, storage doing the same jobs. A phone genuinely is a small computer.

---

How information is measured

Deep down everything - text, images, sound - is stored as numbers built from the bit: a single on/off value, like one light switch. Line up 8 bits and you get 256 patterns - enough for a letter or a shade of colour. That group of 8 bits is a byte, the basic unit.

Unit	Roughly	Note
bit	on/off	the smallest thing there is
byte	8 bits	one letter’s worth
KB (kilobyte)	~1,000 bytes
MB (megabyte)	~1,000 KB	a photo is a few MB
GB (gigabyte)	~1,000 MB	phone storage, RAM
TB (terabyte)	~1,000 GB	big drives

Each step is about ×1000. But drives often count 1 GB as 1024 MB, not 1000 - because computers count in twos (powers of two), and 1024 is the power of two nearest a thousand. That’s why a drive shows slightly less than the number on the box. Nothing is faulty.

The everyday trap - MB vs Mbit

A megabyte (MB) and a megabit (Mbit) are not the same. A byte is 8 bits, so 1 MB = 8 Mbit. File sizes are sold in bytes (a photo is “4 MB”); internet speed is sold in bits (“50 Mbit/s”) - partly because the number looks bigger. So a “50 megabit” line will not move a “50 megabyte” file in one second. Different-sized units.

---

The operating system

Hardware alone does nothing usable - something has to organise it and let a human drive it. That’s the operating system (OS): the master program that manages the whole machine and sits between me and the hardware. Open a program, save a file, get online - it all goes through the OS. Windows, macOS, Linux are OSes; Android and iOS are the phone ones.

Everyday controls: the desktop (background with icons), a taskbar (Windows) or dock (Mac) to launch and switch, and four mouse actions that cover almost everything:

• Click - select / press a button
• Double-click - open a file or program
• Right-click - “what can I do with this?” → menu of options
• Drag - hold and move something

Programs open in windows I can open, close, minimise, resize, and switch between. Moving between windows is basically what “using a computer” feels like all day. (Right-click is the single habit that gets beginners unstuck fastest.)

---

Files, folders, paths

A file is one named item of stored info (a document, photo, song, program). A folder (a.k.a. directory) is a container that groups files and other folders. Folders nest inside folders → a branching folder tree.

Read a file name as name + type. The bit after the dot is the extension, which tells the computer what kind of file it is and which program opens it:

report.pdf   →  "report"  = my chosen name
                ".pdf"     = the type (PDF document)

holiday.jpg  = image      budget.xlsx = spreadsheet

A path is just where a file lives in the tree - which folder, inside which folder. (Same concept returns in a terminal later, typed by hand; only the usage changes.)

Managing files = create, rename, move, copy, delete. Deleted things don’t vanish instantly - they wait in the Recycle Bin (Windows) / Trash (Mac) until it’s emptied, so a single accidental delete is recoverable. A few clearly named folders beats one giant pile every time.

---

Everyday office software

Tool	Examples	For
Word processor	Word, Google Docs	Writing - letters, reports, notes (mostly text)
Spreadsheet	Excel, Google Sheets	Numbers, lists, tables - anything in rows & columns
Presentation	PowerPoint, Google Slides	Slides to show an audience

Save vs Save As - the one that bites people

• Save - update this file with the latest changes (same name, same place).
• Save As - make a new, separate copy (different name or location); the original is left untouched. Use it to keep “draft 1” while starting “draft 2.”
• Export as PDF - a fixed, finished form that looks identical everywhere and isn’t easily edited. Right for a CV, invoice, or official form.

A spreadsheet is a grid of cells in rows (across) and columns (down), each cell holding one value. That plain grid handles a budget or schedule - and grows into a real data tool later.

---

Installing software, and getting unstuck

Installing = adding a new program: download an installer and run it, or get it from an official store (Microsoft Store, Mac App Store, phone app store). The habit that matters most is where it comes from - stick to the maker’s own site or a trusted store. Unofficial download sites are a top way machines pick up harmful software. If I hesitate, that hesitation is worth listening to.

When something goes wrong, work the method restart → read → search → ask:

1. Restart the program (or the computer) and reopen - fixes a large share of freezes.

2. Read any message on screen for a plain-language clue.

3. Search with specific words: program name + what happened (“[program] freezes when opening a file”).

4. Ask, describing what I did, what I expected, and what actually happened.

Broken vs stuck

Stuck = the thing works, I just don’t know the step yet → fix by learning, searching, asking. Broken = the thing itself has failed → fix by repair or reinstall. Beginners assume “broken” when they’re only “stuck.” Run the method first; it tells me which one it is.

---

Your machine vs server vs cloud

The simplest split in computing: something runs on my machine (in front of me) or on someone else’s machine (reached over the internet). Everything else is a variation of that.

A server is a computer built to serve others - store things and answer requests from many computers at once, running around the clock in cooled, secured buildings. Visiting a website = my machine asking a server to send the page. And “the cloud” is just someone else’s computer - my files/services live on a company’s servers instead of only on my device.

My machinelocal - I own it

→

Serversomeone else’s, over a network

→

The cloudservers in a real building = rent

Three tiers - but really one idea: my computer, or someone else’s, reached over the internet.

The cloud is physical

When a big cloud provider has an outage, a startling range of unrelated apps go dark at once - banking, streaming, even smart doorbells - because they quietly rent from the same few providers. Proof the cloud isn’t fluffy: it’s specific buildings full of computers. And cloud storage (with syncing across devices) is safer than a single device but not invincible - keep more than one copy of anything important.

---

Virtualization: one computer acting as many

Virtualization makes one physical computer behave as if it were several separate ones. Each pretend computer is a virtual machine (VM) - it runs with its own operating system, walled off from the others, believing it’s a whole machine, even though it’s software on one physical host underneath.

This is why Windows running on a Mac, or Linux inside Windows, is normal, not broken: the physical machine runs its usual OS, and a VM runs a different OS inside a window. People do it to use a program that only exists elsewhere, or to test safely.

Virtual machine

Emulates a whole computer including its own full OS. Heavier, strongly isolated. This is what runs Windows-on-a-Mac, and much of the cloud.

Container

A lighter, more efficient cousin - shares the host’s OS and packages just the app and what it needs. Used heavily in professional software work; faster and smaller than a full VM.

Two phrases that tie it together

On-premise vs cloud = owning vs renting. Run things on machines I own and keep = on-premise; use someone else’s machines over the internet = cloud. And cloud gaming proves the point: a demanding game runs on a strong-GPU machine in a data centre, and only the video is streamed to my cheap laptop while my button presses go back - “someone else’s computer, on demand.”

---

Internet vs web

Not the same thing. The internet is the global network of connected computers - the infrastructure that lets machines exchange information. The web (World Wide Web) is one service running on it: websites and pages I visit in a browser. Email, video calls, and online games also ride the internet but are not the web. Internet = the road system; web = one kind of traffic on it.

Every web address is a URL, and it reads in parts:

https://  www.example.com  /products/shoes
  │             │                 │
secure     domain name          path
connection (WHO I'm         (which page
(the "s")   talking to)      on that site)

The domain is the part always worth a glance - it tells me who I’m really connected to (a big safety payoff later).

Every visit is a request → response between a client (my device, the asker) and a server (built to answer):

Clientmy browser

→

DNS lookup”where does this domain live?”

→

Request”send me this page”

→

Server respondspage sent back in small packets

→

Browser reassemblesdraws the page - under a second

Press enter: find the address (DNS), ask (HTTP request), get the page back in packets, reassemble and draw. One computer asked, another answered.

The jargon, once

IP = the numeric address a device is found at. DNS = the lookup that turns a readable domain into that IP address. HTTP(S) = the request/response method the web speaks (the S = secure, encrypted). Packets = the small pieces a page is broken into for delivery, then reassembled.

---

Networks you actually use

A network is just computers connected so they can exchange information. The names describe the size or job:

Type	Stands for	What it is
LAN	Local Area Network	Small & local - home or one office
WAN	Wide Area Network	Spans distances; the internet is the biggest WAN
Wi-Fi	-	Wireless way onto a LAN (no cable)
Mobile	4G / 5G	Cellular data from a carrier, on the move
VPN	Virtual Private Network	Encrypted tunnel to another network across the public internet
Router	-	The box that joins my LAN to the internet and directs traffic

Why work asks for a VPN

Companies keep internal systems reachable only from inside the company network. Working from home, I connect through a VPN first - my laptop opens a secure tunnel into the company network, then I reach internal systems as if sitting in the office, traffic protected along the way. So the day-one “connect to the VPN” ask = the company extending its safe internal network out to me. (An IP address identifies a device for delivery, not a person’s identity card.)

---

Using a browser, and searching well

A browser (Chrome, Firefox, Edge, Safari) requests and displays web pages. Its everyday parts: tabs (several pages open at once), the address bar (shows the URL, and where I type where to go), back / forward, and refresh (asks the server for a fresh copy - good when a page looks stuck). A bookmark saves a page’s address for one-click return; history is the automatic record of where I’ve been. Downloads land in the Downloads folder - a download is just a new file in a known place.

1. Be specific. “Laptop problem” returns an ocean; “laptop battery drains fast when closed” returns answers. Include distinctive words - product names, exact error text.

2. Skim past the ads. The first few results are often paid/sponsored (labelled). The top real result is just the best word-match, not a guarantee of truth.

3. Change the words, don’t repeat them. If a search misses, rephrase or add a distinctive detail. Two or three reworded tries beat one repeated harder.

---

Revision summary

Must-know	One-line recall
CPU / RAM / storage	CPU does the work, RAM = working space (do more at once), storage = keep things when off
RAM vs storage upgrade	More RAM = faster multitasking; more storage = hold more - not the same fix
GPU	Graphics and video - and now the engine behind AI training/running
Bit vs byte	8 bits = 1 byte; everything is stored as on/off bits
Size ladder	KB→MB→GB→TB, each ~×1000; 1 GB often 1024 MB (computers count in twos)
MB vs Mbit	1 MB = 8 Mbit; files sold in bytes, internet speed in bits
Operating system	Master program between me and the hardware (Windows, macOS, Linux, Android, iOS)
Right-click	”What can I do with this?” - the fastest unstuck habit
File / folder / path	File = named item, folder = container, path = where it lives in the tree
Extension	The bit after the dot = the file’s type and which program opens it
Save vs Save As	Save = update this file; Save As = new separate copy; PDF = fixed, final form
Install safely	Only from the maker’s site or a trusted store
Stuck vs broken	Stuck = don’t know the step yet; broken = it failed - run restart/read/search/ask first
Server	A computer built to answer requests from many others, around the clock
The cloud	Just someone else’s computer - real servers in real buildings
On-prem vs cloud	Owning vs renting
Virtualization	One physical machine acting as many VMs, each with its own OS
VM vs container	VM = whole OS, heavy; container = shares host OS, light
Internet vs web	Internet = the network; web = one service (sites) running on it
URL parts	https (secure) · domain (who) · path (which page)
Client → server	Every visit: DNS lookup → HTTP request → page back in packets → reassembled
LAN vs WAN	LAN = local; WAN = wide; internet is the biggest WAN
VPN	Encrypted tunnel into another network - how home workers reach internal systems
Router	The doorway between my LAN and the internet
Searching well	Specific words, skim past ads, change the words when a search misses