Tech in Diagrams

What is an Operating System?

An operating system sits between applications and hardware, sharing the machine safely between programs.

Beginner 4 min IT Fundamentals
Apps · operating system · hardware
  • Requests and answers
  • Scheduling and memory
  • Files and storage
  • Permission check
USERYou click and typeinside applications.BrowserProcess 1041Own memory, own turnon the processor.Text editorProcess 1188Own memory, own turnon the processor.Background serviceProcess 0342Own memory, own turnon the processor.ISOLATIONOne app crashes— the rest continueSeparate memory and turns letthe OS stop one process alone.strong, not absoluteSystem callsthe only doorway — open · read · write · allocate · sendrequest in / answer outCPU SCHEDULINGWho runs nextGives each process short turnson the processor, in order.MEMORY MANAGEMENTProtected spaceMaps memory per process so onecannot read another's space.PERMISSIONSMay you?Checks the user and processbefore granting access.FILESYSTEMOpen · read · writeTurns file names into blockson a storage device.DEVICES · DRIVERSSpeaks to hardwareKeyboard, display, disk, network —apps go through drivers.CPUExecutes instructionsreached only through the OSRAMPhysical memoryreached only through the OSStorageDisk / SSDreached only through the OSKeyboard · display · networkInput and output devicesreached only through the OSOPENING A FILE — ONE REQUEST, END TO END
Applications never touch hardware directly. Every request passes through the operating system, which decides who runs next, which memory belongs to whom, whether the access is allowed, where the file lives and which driver speaks to the device.

Hover an application, a control surface, a hardware resource or the open-file walkthrough to isolate its path; click any part for a short explanation.

Why it matters

  • Isolation between processes is what stops one misbehaving program from taking the whole machine down.
Next conceptWhat is a Server?A server is a computer whose job is to answer requests from other computers, continuously.