Lesson 1 of 4 · 7 min
What an operating system does
The kernel, processes, files and user accounts: four ideas behind everything your Mac does.
You open an app, save a document, plug in a drive. None of that reaches the hardware directly: a program called the operating system sits between every action you take and the chip, memory and disk underneath. Understanding its four main jobs makes the rest of this course, and the choices you make about your Mac, much easier to follow.
The kernel: in charge of the hardware
The kernel is the core of the operating system, the part that decides which program gets to use the processor next, which app can read which piece of memory, and how data reaches the disk. Apple’s security documentation describes system security as ‘responsible for controlling access to system resources in Apple devices without compromising usability’, covering the boot process and ‘protection of computer system resources such as CPU, memory, disk, software programs, and stored data’. Every other program, including the apps you open, asks the kernel for these resources rather than touching them directly.
That control starts before macOS even finishes loading. Apple calls this secure boot: a chain of checks, starting in the hardware itself, where ‘each step is designed to ensure that the next is functioning properly before handing over control’. If an early step is untrustworthy, the ones after it are not allowed to run.
Processes: programs while they run
A process is a program while it is executing: your browser, your mail client, a background service checking for updates. The kernel keeps dozens of these running at once by giving each a slice of time on the processor and a private area of memory. Later lessons in this course build on this: the app sandbox exists specifically to stop one process from reaching into another’s memory or files.
Files: organized, and gated by permission
The operating system also organizes storage into a file system: folders, files, and metadata about who is allowed to read or change each one. That gatekeeping is what makes it possible for two people, or two apps, to share the same disk without automatically seeing each other’s data.
Users: separate identities on one machine
Finally, the operating system tracks who is doing the asking. On a Mac, every person who logs in has an account, and accounts come in different types. Apple’s Mac User Guide explains that an administrator ‘can add and manage other users, install apps, and change settings’, while a standard account, ‘set up by an administrator’, ‘can install apps and change their own settings, but can’t add other users or change other users’ settings.’ The account you use day to day decides what you, and any software running as you, are allowed to touch.
| Idea | What it manages | Why it matters to you |
|---|---|---|
| Kernel | The processor, memory and boot process | Everything else depends on it behaving correctly |
| Processes | Programs while they run | Isolating them limits how far one compromised app can reach |
| Files | Storage and who may read or write it | The basis for every permission prompt you will see |
| Users | Which person or account is asking | Decides whether an action needs your approval |
Key takeaways
- The kernel is the core program that controls the processor, memory and disk; apps ask it for access rather than reaching hardware directly.
- Secure boot checks each step of startup before handing control to the next, so an untrustworthy step cannot proceed.
- A process is a program while it runs; the operating system isolates processes from each other’s memory.
- File systems track who may read or change each file, the basis for every permission you will meet later in this course.
- User accounts come in different types on macOS: an administrator can change settings and manage other accounts, a standard account cannot.
Check yourself
1. What does the kernel do?
- It stores your files in the cloud
- It is the core of the operating system that controls the processor, memory and disk — Right.
- It is a type of app you can install
- It only runs while you are connected to the internet
The kernel is the part of the operating system that manages hardware resources for every other program.
2. What is a process?
- A folder of documents
- A user account
- A program while it is executing — Right.
- A type of file permission
A process is a running instance of a program; the operating system gives each one processor time and its own memory.
3. According to Apple’s Mac User Guide, what can a standard account do that an administrator account can also do?
- Add new users to the Mac
- Install apps and change its own settings — Right.
- Change other users’ settings
- Bypass the login password for other accounts
Standard accounts can install apps and change their own settings, but only an administrator can add users or change other accounts.
4. What is secure boot designed to do?
- Speed up how fast apps open
- Check each step of startup before handing control to the next — Right.
- Back up your files automatically
- Let any app access any file without a prompt
Apple describes secure boot as a chain of trust where each step verifies the next before handing over control.
Do it with FireAI
Put this lesson into practice on your own Mac.
- Answer your first connection prompt, and what each lifetime means — Understand exactly what you’re approving the first time FireAI asks.
- Find apps with known security flaws — Close known holes before anyone uses them: update the one app that needs it.
- See which app turns on your camera or microphone, and where its traffic goes — Know which app can see or hear you, not just that something can.
Sources
Put it into practice on your Mac
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