Roadmap › How Computers Work — CPU, Memory, OS, Processes and Threads › Module: Operating System, Processes and Threads
Lessons in this course (11)
7. What the operating system does
Basic★ Must knowLesson 7 of 11
The OS kernel sits between programs and hardware:
| Job | What it means |
|---|---|
| Process management | Create/stop processes, schedule threads on CPU cores |
| Memory management | Virtual memory, paging, protection |
| File system | Files, folders, permissions (NTFS, ext4) |
| Device drivers & I/O | Disk, network, USB, GPU |
| Networking | TCP/IP stack, sockets |
| Security | Users, permissions, isolation |
User mode vs kernel mode: your code runs in user mode; when it needs the OS (read a file, send a packet, allocate pages) it makes a system call, the CPU switches to kernel mode, the kernel does the work and returns. System calls are relatively expensive — that's why buffering (reading 64 KB at once instead of one byte at a time) matters.