DistOS 2014W Lecture 1
What is an Operating System?
In general, an OS allows you to run the same applications on (slightly) different hardware. Here are a few thoughts on what the responsibilities and functionality are of modern operating systems, and what we expect from something calling itself an OS:
- A hardware abstraction layer such that diverse hardware resources can be accessed uniformly by software
- A consistent execution environment, which hardware doesn't provide (ie. code written to interface &emdash; think portable code)
- Management of I/O (such as user I/O, machine I/O i.e. network I/O, sensors, videos, etc.)
- Resource management through multiplexing and policy use
- Multiplexing (sharing): one resource wanted by multiple users
- Communication infrastructure (for example inter-process communication) between the users (process, applications) of the operating system.
- Management of synchronization and concurrency issues
We could also say that an OS turns the computer you have into the computer you want. An OS can be defined by the role it plays in the programming of systems. It takes care of resource management and creates abstraction. An OS turns hardware into the computer/API/interface we want to program.
This is similar to how the browser is becoming the OS of the web. The browser is the key abstraction needed to run web apps. It is the interface web developers target. It doesn't matter what you consume a given website on (eg. a phone, tablet, etc.), the browser abstracts the device's hardware and OS away.
What is a distributed OS?
Anil prefers to think of this 'logically' rather than functionally/physically. This is because the old distributed operating system (DOS) model applies to systems today which we don't consider distributed (ie. managing multiple cores, etc). The traditional definition is systems that manage their resources over a Network.
A lot of these definitions are hard to peg down because simplicity always gets in the way of truth. These concepts to do not fit into well defined classes.
To draw parallels to our previous definition of operating systems, a distributed OS takes the distributed pieces of a system, and turn it into the system you want.
It is good to think about about DOSes within the context of who/what is in control, in terms of who makes and enforces decisions in DOSes. In essence, who is in charge? The traditional kernel-process model is a dictatorship, an authoritarian model of control. The kernel controls what lives or dies. The internet, in contrast, is decentralised (eg. DNS&emdash;to some extent, ignoring centralized roots). Distributed systems may have distributed policies where there is not one source of power. Even in DOS we see instances of authoritarian/centralized approaches one example being the walled garden model employed by Apple's iOS. Anil's observation is that centralized systems has an inherent fragility built into and these kind of systems come into existence and disappear after a while. Examples being AOL, Myspace. Even Facebook also looks to be a possible candidate for a similar fate. Also, concentrations on policy will tend to fall apart in the future.