Can anyone tell me about "Layered operating system"?

Answer 1

Unix is a layered operating system. The innermost layer is the hardware that provides the services for the OS. The operating system, referred to in Unix as the kernel, interacts directly with the hardware and provides the services to the user programs. These user programs don't need to know anything about the hardware. They just need to know how to interact with the kernel and it's up to the kernel to provide the desired service. One of the big appeals of Unix to programmers has been that most well written user programs are independent of the underlying hardware, making them readily portable to new systems.

User programs interact with the kernel through a set of standard system calls. These system calls request services to be provided by the kernel. Such services would include accessing a file: open close, read, write, link, or execute a file; starting or updating accounting records; changing ownership of a file or directory; changing to a new directory; creating, suspending, or killing a process; enabling access to hardware devices; and setting limits on system resources.

Unix is a multi-user, multi-tasking operating system. You can have many users logged into a system simultaneously, each running many programs. It's the kernel's job to keep each process and user separate and to regulate access to system hardware, including cpu, memory, disk and other I/O devices.

Answer 2

OS Layers are logical building blocks of an operating system. You can imagine, as you go from the top to the bottom first you see images, button, colors, sounds-, then comes a lot of 'primitive' English, scramble with a lot of commands-, then the commands form only a couple of letters and numbers-, and finally you end up looking at the mythological 0's and 1's, the 'computer language', as thought in school. We don't dive any deeper, becouse we might hit some resistors or jumpers on the motherboard. ;)

Answer 3

A layered OS has different levels that ineract with different things.

Windows, for example, has a graphical user interface layer. Which is what users interact with. Below that is another layer that actually interacts with data on your PC. Below that, is a level that interacts with hardware. There are other levels/layer arrangements, but that's the general idea.

This is done to keep users or programs from making your computer do things that could be damaging. It's also a big part of digital encryption and protection schemes.