Operating Systems: Week 7

 During this week, we have gone through the last chapters of this course. We went over IO devices, hard drives, files, and directories, as well as the file systems. When I learned about chapter 36 on IO devices, we went over how the OS actually talks to the devices. We reviews the computer architecture and looked at the PC architecture. There are two I/O devices, which are block devices and character devices, also known as stream devices. The block devices are hard drives, and the character devices are printers, keyboards, and mouses.

There are three different ways that the CPU interacts with IO, and those are polling, interrupts, and direct memory access. Polling is better when we have a really low latency. Interrupt is better when there is a need for a little bit of data intermittently. Direct memory access is better when there is an abundance of data that we want to move.

In chapter 37, when we went over hard drives, I learned more about them. I also learned how to calculate the following: rotational delay of a hard driven given its RPM value, the time for a read or write operation, and the time for a group at read or write operations-random or sequential. To calculate the average rotational delay, we multiply the time for one rotation and ½. We also consider what we want our output to be, either minutes, seconds, or milliseconds, which includes more math. To calculate the time for a read or write, we use the following formula: total time = rotational delay + seek time + transfer time.

There is more information on what I learned this week, but now I have to continue to focus on my Final!