Date: December 26, 2024

Topic: Principle of Abstraction

Recall

Hardware abstraction layers from very low level to much higher levels. The OS acts as a broker between applications and physical resources

Notes

Abstractions in Software

Hierarchy of abstractions for applications

• At the lowest level are transistors and at the highest are applications
• For an application like Google Earth, interactions by the users cause a traversal between the different abstractions
• Operating System acts as a broker between application at the top and physical resources like CPU, memory, etc.

<aside> 📌 SUMMARY: OS acts as a broker between applications and physical resources

</aside>

Date: December 30, 2024

Topic: Hardware Resources

Recall

The internal organization for many devices are consistent, having CPU, storage, controllers, etc

Notes

Hardware Resources

Internal Organization

• Regardless of different manifestations (laptops, tablets, servers), the internal organization is the same for all of them

• CPU is connected to a conduit (BUS) that can interact with memory holding the instructions and data for the CPU to execute.
• Storage is used for file persistence and data produced during computation. CPU also uses the BUS to interact with Storage through a Contr.
• Other peripheral devices (camera, microphone) are accessed the same way through a Contr. as well
• The CPU also uses a Contr. to interact with the Network
• Contr. may also have DMA (Direct Memory Access) to move data quickly between I/O device and memory (high speed devices)

The BUS is organized as a System BUS and I/O BUS. The System BUS is much faster all it needs to cater to all clients wanting access to memory while the I/O BUS is slower and intended for devices to communicate with CPU

I/O BUS Organization

The BUS is split into the System BUS and I/O BUS, with a bridge connecting them. The BUSes allows for ferrying of data

System BUS is much faster than I/O BUS

System BUS

• Synchronous comms device between the CPU and memory
• System BUS has comms bandwidth that is >> comms bandwidth in I/O BUS
• Has higher speed as it needs to cater to all clients that may want access to memory

I/O BUS

• Primarily intended for devices to communicate with CPU
• Individual needs of each devices (e.g., network, storage, peripherals) < cumulative bandwidth available for CPU to communicate with memory
• Has lower speed

Bridge

• Connects both BUSes
• Can be a specialized I/O processor for scheduling the devices that need to comms with CPU or memory
• Controls who has access to I/O BUS among set of competing devices for attention by CPU and communicating intent of these I/O devices either directly with memory or via CPU.

<aside> 📌 SUMMARY: Internal organization across different devices are usually consistent, with the communication channels established above. Hence many key concepts of OS apply to all devices.

</aside>

Date: January 1, 2025

Topic: OS Functionality