2.4 Structure of Operating System

✅ Three types of structure of OS

• There are three types
• All the OS since year 2011 more or less, are evolving towards Hybrid

1️⃣ Monolithic

• An OS is monolitic if the software is a huge block
• huge block of SW, unique, only one software
• and does all the fuctions, it is in charge of everything

• kernel is active/works

• 💡 Kernel: this huge one, unique software that does everything is called kernel

• over this kernel, you can install other applications for customers
• However, the kernel is unmodifiable 🙅🏻‍♀️
• 👎🏻 NOT flexible

• 👎🏻 NOT adaptable to your needs

  • cannot even change the color of your OS
• 👀 Windows is not monolithic ❌
• 👀 Symbian OS was monolithic

• 👀 airport tower OS is monolithic, use modified symbian OS

• 👍🏻 more secure
• as nobody can not change anything, more difficult to corrupt
• very secure

2️⃣ Micro kernel OS with IPC

• the kernel(SW) is small

• you can add more/extra functionalities to the kernel

• 💡 User servers: These extra functionalities are called user servers
• installed to give extra services to the users
• you add more service to the kernels
• 👀 Service pack for windows

• when you add a service pack to windows, you are adding a user server, new functionality to kernel

• 👍🏻 more adaptative to user needs
• 👎🏻 less secure, kernel is not so protected

• 👀 Windows

• In Micro kernel OS, the kernel only gets orders/only gets disturbed only when there is high relevence
• so only when there is an emergency
• 💡 IPC Inter Process Communications: emergencies thrown to the kernel
• if there is one IPC, not very urgent
• but if there are hundreads of IPCs⬆️⬆️⬆️, big big emergency!
• the number of IPC that you see in a a terminal is an indicator of an importance of an error in the system
• as system experts, you need to check the frequency of IPC

• If the frequency is high⬆️, need to mirror the servers before the breakdown

• 👀 Whatsapp everyday at 2am, checks the IPCs
• to prevent failure, and became a more stable service

3️⃣ Hybrid

• mix of Monolithic and Microkernel
• the kernel is half size
• so the kernel works/active, has important functions
• and has user servers to help the kernel
• security layer between the server and the kernel

• In hybrid, there is NO IPCs ❌ , bc we have security layer

• 👍🏻 adaptative, as it has user servers
• 👍🏻 safe, as it has a security layer

• 👍🏻 even without installing so many user service, it is still active as kernel works

  • as kernel is working, you can run it wo so many user service

• 👀 Linux is hybrid structure

• Best structure of OS
• So all the OS since year 2011 more or less, are evolving towards hybrid

⭐️ Exam Questions

❓ Look at the picture and answer some questions

❓ Are there user servers?
- only Microkernel and Hybrid

❓ Are there IPCs? Which one has IPCs?
- Only Microkernel has IPCs, so last picture

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