I've read in Tanenbaum's Computer architecture that OS's kernel doesn't necessarily have to be stored as executable file, but can be directly implemented in circuit and perform syscalls and other functions by hardware. Are there real examples of such systems (say, Linux or any micro-OS, specially developed for implementing in circuits)?
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From my research I cannot find what kernel type is being used in eCos, such as monolithic or micro-kernel. All I could find from my research is that the kernel is a real-time one or websites just describe it as the eCos kernel, does this mean it is a custom made kernel?
What I know about eCos is that it is a hard RTOS although is somewhat vulnerable in terms of security, uses priority, queue based scheduling.
A micro-kernel is:
... the near-minimum amount of software that can provide the mechanisms
needed to implement an operating system (OS). These mechanisms include
low-level address space management, thread management, and
inter-process communication (IPC).
(Wikipedia 11 Dec 2018)
The eCos kernel is described in its Reference Manual thus:
It provides the core functionality needed for developing
multi-threaded applications:
The ability to create new threads in the system, either during startup
or when the system is already running.
Control over the various threads in the system, for example
manipulating their priorities.
A choice of schedulers, determining which thread should currently be
running.
A range of synchronization primitives, allowing threads to interact
and share data safely.
Integration with the system's support for interrupts and exceptions.
It is quite clearly by comparison of these descriptions a micro-kernel. Other services provided by eCos such as file-systems, networking and device drivers are external and separable from the kernel. That is to say, you can deploy the kernel alone without such services and it remains viable.
In a monolithic kernel, these services are difficult or impossible to separate as they are an intrinsic part of the whole. Unlike eCos mand most other RTOS they do not scale well to small hardware platforms common in embedded systems. Monolithic kernels are suited to desktop and general purpose computing platforms, because the platforms themselves are monolithinc - a PC without a filesystem, display, keyboard etc, is not really viable, whereas in an embedded system that is not the case.
While Linux, and even Windows are used in embedded systems, a micro-kernel is deployable on platforms with a few tens of kilo-bytes of memory, whereas a minimal embedded Linux for example requires several mega-bytes and will include a great deal of code that your application may never use.
Ultimately the distinction is perhaps irrelevant, as is the terminology. It is what it is. You do not choose your kernel or OS on this criteria, but rather whether it provides the services you require, runs on your target, and fits in the available resource.
I think it is a monolithic kernel. If you review this page: http://ecos.sourceware.org/getstart.html
It is used instead of linux kernel and linux kernel support monolithic kernels. In addition, if it was a micro kernel , they would highlight the kernel type like QNX Kernel type which is micro kernel
I need to know Does a operating system design for specific processors category?
and also can any operating system run on any microprocessor?
Generally speaking, an operating system is not designed for a specific processor; though some do make assumptions about the hardware and computer system over all that might not be available in all systems. That said, for an operating system to run on a partical architecture, there is usually code that performs some specific, critical functions that is implemented for a specific architecture, frequently being written in assembly (I know of no OS that doesn't do this). To enable a new architecture, this code needs to be rewritten for the new machine, so that means new assembly most of the time. As mentioned in the comments, there are operating systems that only run on a single architecture like Windows, while others have these specific components for a number of architectures and thus can run on a number of processors like Linux. Note however the same exactly binary will not run across architectures, the operating system needs to be rebuilt for each architecture and possibly even for the same architecture if the system itself is different enough (as can be the case with some small MCUs).
So to answer your two questions directly: no, an OS is not uaually designed for a specific processor, and no, any OS cannot run on any processor.
Historically, operating systems have been designed for specific hardware. In some cases, such as eunuchs, the system was reworked so that it could be ported to multiple systems.
M$ ported Windoze to the Alpha processor in order to placate Digital and avoid lawsuits.
[C]an any operating system run on any microprocessor?
No.
When reading the documentation of BLE chip from a semiconductor manufacturer that there is a small real time kernel on board, not OS. This is probably just a stupid question, but what would be the difference between a full fledged RTOS vs a real time kernel in such a scenario.
There are a variety of opinions on that question. One, held by systems programmers and the like, is that an OS kernel is a minimal set of services to abstract the underlying computer hardware, making it easier to write an OS or even applications on the machine. OS kernels typically operate in their own space, separate from user space where the rest of the OS (or even applications) reside. There is also the concept of a microkernel (and nanokernel), which is intended specifically to serve higher level (e.g., user space) OS services--although different microkernels partition OS services differently in kernel vs. user space. Check Wikipedia as a start (although some of its related entries have some factual errors).
Sometimes the embedded computing community refers to a kernel as a minimal OS, expecting applications, not more OS functionality, to use the kernel.
This may seem like an insignificant distinction, but it does effect the design and implementation of the kernel.
Recently I heard the term meta-operating system while I was learning ros. Could you please help me to differentiate between operating system and meta-operating system?
What ROS is and is not is best explained in this paper.
To cite the intodruction at ros.org:
It provides the services you would expect from an operating system, including hardware abstraction, low-level device control, implementation of commonly-used functionality, message-passing between processes, and package management. It also provides tools and libraries for obtaining, building, writing, and running code across multiple computers.
You'll also find a good explanation in this wiki. The basic difference is that a meta operating system is built on top of the operating system and allows different processes (nodes) to communicate with each other at runtime.
I saw a question on Linux Kernel. While reading that I had this doubt.
The Windows NT branch of windows has a Hybrid Kernel. It's neither a monolithic kernel where all services run in kernel mode or a Micro kernel where everything runs in user space. This provides a balance between the protection gained from a microkernel and the performance that can be seen in a monolithis kernel (as there are fewer user/kernel mode context switches).
As an example, device drivers and the Hardware Abstraction layer run in kernel node but the Workstation service runs in user mode. The wikipedia article on Hybrid Kernels has a good overview.
The Windows Internals book gives an explanation for the hybrid approach
... The Carnegie Mellon University Mach
operating system, a contemporary
example of a microkernel architecture,
implements a minimal kernel that
comprises thread scheduling, message
passing, virtual memory, and device
drivers. Everything else, including
various APIs, file systems, and
networking, runs in user mode.
However, commercial implementations of
the Mach microkernel operating system
typically run at least all file system,
networking, and memory management
code in kernel mode. The reason is
simple: the pure microkernel design is
commercially impractical because it’s
too inefficient.
According to Wikipedia it's a Hybrid kernel. Which may or may not be just marketing speak for about the same as a monolithic one. The graphic on the latter page does make some things clearer, though.
Most importantly, almost no program on Windows uses the kernel API directly. And the complete Windows API subsystem resides in user space which is a rather large part of the OS as we see it. And in more recent versions Microsoft began to pull more and more device drivers from kernel space into user space (which is especially a good idea with certain drivers, such as for video cards which are probably as complex as an operating system on their own).
hyru hybrid kernel is the name of the Kernel that Windows systems after Windows 98, before that it was a GUI overlaid on DOS using a monolithic Kernel.