Computer Architecture And Operating Systems Pdf


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The kernel is a computer program at the core of a computer's operating system that has complete control over everything in the system. On most systems, the kernel is one of the first programs loaded on startup after the bootloader. The critical code of the kernel is usually loaded into a separate area of memory, which is protected from access by application programs or other, less critical parts of the operating system.

Deep Blue Home Login. JavaScript is disabled for your browser. Some features of this site may not work without it. Abstract: Good computer architecture design requires a thorough understanding of the interactions between the software and the hardware. Recognizing this fact, architects spend considerable effort studying application code behavior and basing their design decisions on quantitative analysis that considers how the architecture can best support application software.

Computer Architecture - Operating Systems (CAOS)

The kernel is a computer program at the core of a computer's operating system that has complete control over everything in the system. On most systems, the kernel is one of the first programs loaded on startup after the bootloader. The critical code of the kernel is usually loaded into a separate area of memory, which is protected from access by application programs or other, less critical parts of the operating system. The kernel performs its tasks, such as running processes, managing hardware devices such as the hard disk , and handling interrupts, in this protected kernel space.

In contrast, application programs like browsers, word processors, or audio or video players use a separate area of memory, user space.

This separation prevents user data and kernel data from interfering with each other and causing instability and slowness, [1] as well as preventing malfunctioning application programs from crashing the entire operating system.

The kernel's interface is a low-level abstraction layer. When a process requests a service to the kernel, it must invoke a system call , usually through a wrapper function that is exposed to userspace applications by system libraries which embed the assembly code for entering the kernel after loading the CPU registers with the syscall number and its parameters e. There are different kernel architecture designs.

Monolithic kernels run entirely in a single address space with the CPU executing in supervisor mode , mainly for speed. Microkernels run most but not all of their services in user space, [3] like user processes do, mainly for resilience and modularity. Instead, the Linux kernel is monolithic, although it is also modular, for it can insert and remove loadable kernel modules at runtime.

This central component of a computer system is responsible for 'running' or 'executing' programs. The kernel takes responsibility for deciding at any time which of the many running programs should be allocated to the processor or processors. Random-access memory RAM is used to store both program instructions and data. Often multiple programs will want access to memory, frequently demanding more memory than the computer has available.

The kernel is responsible for deciding which memory each process can use, and determining what to do when not enough memory is available. Key aspects necessary in resource management are defining the execution domain address space and the protection mechanism used to mediate access to the resources within a domain. These implementations may be within the kernel itself or the kernel can also rely on other processes it is running.

Although the kernel must provide IPC in order to provide access to the facilities provided by each other, kernels must also provide running programs with a method to make requests to access these facilities.

The kernel is also responsible for context switching between processes or threads. The kernel has full access to the system's memory and must allow processes to safely access this memory as they require it.

Virtual addressing allows the kernel to make a given physical address appear to be another address, the virtual address. Virtual address spaces may be different for different processes; the memory that one process accesses at a particular virtual address may be different memory from what another process accesses at the same address.

This allows every program to behave as if it is the only one apart from the kernel running and thus prevents applications from crashing each other. On many systems, a program's virtual address may refer to data which is not currently in memory. The layer of indirection provided by virtual addressing allows the operating system to use other data stores, like a hard drive , to store what would otherwise have to remain in main memory RAM.

As a result, operating systems can allow programs to use more memory than the system has physically available. When a program needs data which is not currently in RAM, the CPU signals to the kernel that this has happened, and the kernel responds by writing the contents of an inactive memory block to disk if necessary and replacing it with the data requested by the program. The program can then be resumed from the point where it was stopped.

This scheme is generally known as demand paging. Virtual addressing also allows creation of virtual partitions of memory in two disjointed areas, one being reserved for the kernel kernel space and the other for the applications user space. The applications are not permitted by the processor to address kernel memory, thus preventing an application from damaging the running kernel.

This fundamental partition of memory space has contributed much to the current designs of actual general-purpose kernels and is almost universal in such systems, although some research kernels e. To perform useful functions, processes need access to the peripherals connected to the computer, which are controlled by the kernel through device drivers.

A device driver is a computer program that enables the operating system to interact with a hardware device. It provides the operating system with information of how to control and communicate with a certain piece of hardware.

The driver is an important and vital piece to a program application. The design goal of a driver is abstraction; the function of the driver is to translate the OS-mandated abstract function calls programming calls into device-specific calls. In theory, the device should work correctly with the suitable driver.

Device drivers are used for such things as video cards, sound cards, printers, scanners, modems, and LAN cards. A kernel must maintain a list of available devices. This list may be known in advance e.

In plug-and-play systems, a device manager first performs a scan on different peripheral buses , such as Peripheral Component Interconnect PCI or Universal Serial Bus USB , to detect installed devices, then searches for the appropriate drivers. Important decisions have to be made when designing the device management system, as in some designs accesses may involve context switches , making the operation very CPU-intensive and easily causing a significant performance overhead.

In computing, a system call is how a process requests a service from an operating system's kernel that it does not normally have permission to run. System calls provide the interface between a process and the operating system.

Most operations interacting with the system require permissions not available to a user-level process, e. A system call is a mechanism that is used by the application program to request a service from the operating system.

They use a machine-code instruction that causes the processor to change mode. An example would be from supervisor mode to protected mode. This is where the operating system performs actions like accessing hardware devices or the memory management unit. Generally the operating system provides a library that sits between the operating system and normal user programs.

The library handles the low-level details of passing information to the kernel and switching to supervisor mode. System calls include close, open, read, wait and write. To actually perform useful work, a process must be able to access the services provided by the kernel. This is implemented differently by each kernel, but most provide a C library or an API , which in turn invokes the related kernel functions. The method of invoking the kernel function varies from kernel to kernel. If memory isolation is in use, it is impossible for a user process to call the kernel directly, because that would be a violation of the processor's access control rules.

A few possibilities are:. An important consideration in the design of a kernel is the support it provides for protection from faults fault tolerance and from malicious behaviours security. These two aspects are usually not clearly distinguished, and the adoption of this distinction in the kernel design leads to the rejection of a hierarchical structure for protection. The mechanisms or policies provided by the kernel can be classified according to several criteria, including: static enforced at compile time or dynamic enforced at run time ; pre-emptive or post-detection; according to the protection principles they satisfy e.

Support for hierarchical protection domains [10] is typically implemented using CPU modes. Many kernels provide implementation of "capabilities", i. A common example is file handling: a file is a representation of information stored on a permanent storage device. The kernel may be able to perform many different operations, including read, write, delete or execute, but a user-level application may only be permitted to perform some of these operations e.

A common implementation of this is for the kernel to provide an object to the application typically so called a "file handle" which the application may then invoke operations on, the validity of which the kernel checks at the time the operation is requested. Such a system may be extended to cover all objects that the kernel manages, and indeed to objects provided by other user applications. An efficient and simple way to provide hardware support of capabilities is to delegate to the memory management unit MMU the responsibility of checking access-rights for every memory access, a mechanism called capability-based addressing.

An alternative approach is to simulate capabilities using commonly supported hierarchical domains. In this approach, each protected object must reside in an address space that the application does not have access to; the kernel also maintains a list of capabilities in such memory. When an application needs to access an object protected by a capability, it performs a system call and the kernel then checks whether the application's capability grants it permission to perform the requested action, and if it is permitted performs the access for it either directly, or by delegating the request to another user-level process.

The performance cost of address space switching limits the practicality of this approach in systems with complex interactions between objects, but it is used in current operating systems for objects that are not accessed frequently or which are not expected to perform quickly.

If the firmware does not support protection mechanisms, it is possible to simulate protection at a higher level, for example by simulating capabilities by manipulating page tables , but there are performance implications. An important kernel design decision is the choice of the abstraction levels where the security mechanisms and policies should be implemented.

Kernel security mechanisms play a critical role in supporting security at higher levels. One approach is to use firmware and kernel support for fault tolerance see above , and build the security policy for malicious behavior on top of that adding features such as cryptography mechanisms where necessary , delegating some responsibility to the compiler. The lack of many critical security mechanisms in current mainstream operating systems impedes the implementation of adequate security policies at the application abstraction level.

Typical computer systems today use hardware-enforced rules about what programs are allowed to access what data. The processor monitors the execution and stops a program that violates a rule, such as a user process that tries to write to kernel memory. In systems that lack support for capabilities, processes are isolated from each other by using separate address spaces.

An alternative approach is to use language-based protection. In a language-based protection system , the kernel will only allow code to execute that has been produced by a trusted language compiler. The language may then be designed such that it is impossible for the programmer to instruct it to do something that will violate a security requirement. Examples of systems with language-based protection include JX and Microsoft 's Singularity.

Edsger Dijkstra proved that from a logical point of view, atomic lock and unlock operations operating on binary semaphores are sufficient primitives to express any functionality of process cooperation. Similar to physical memory, allowing applications direct access to controller ports and registers can cause the controller to malfunction, or system to crash.

With this, depending on the complexity of the device, some devices can get surprisingly complex to program, and use several different controllers. Because of this, providing a more abstract interface to manage the device is important. This interface is normally done by a device driver or hardware abstraction layer. Frequently, applications will require access to these devices.

The kernel must maintain the list of these devices by querying the system for them in some way. When an application requests an operation on a device Such as displaying a character , the kernel needs to send this request to the current active video driver. The video driver, in turn, needs to carry out this request.

This is an example of inter-process communication IPC. Naturally, the above listed tasks and features can be provided in many ways that differ from each other in design and implementation. The principle of separation of mechanism and policy is the substantial difference between the philosophy of micro and monolithic kernels.

Because the mechanism and policy are separated, the policy can be easily changed to e.

Chapter 4: Operating systems and computer architecture

This book provides computer engineers, academic researchers, new graduate students, and seasoned practitioners an end-to-end overview of virtual memory. We begin with a recap of foundational concepts and discuss not only state-of-the-art virtual memory hardware and software support available today, but also emerging research trends in this space. The span of topics covers processor microarchitecture, memory systems, operating system design, and memory allocation. We show how efficient virtual memory implementations hinge on careful hardware and software cooperation, and we discuss new research directions aimed at addressing emerging problems in this space. Virtual memory is a classic computer science abstraction and one of the pillars of the computing revolution. It has long enabled hardware flexibility, software portability, and overall better security, to name just a few of its powerful benefits. Nearly all user-level programs today take for granted that they will have been freed from the burden of physical memory management by the hardware, the operating system, device drivers, and system libraries.

Performance is not the only important metric anymore, and new metrics such as security, power, total throughput, Quality of Service are becoming more and more important. It seems clear that neither the hardware nor the software alone can achieve the desired performance and, at the same time, be compliant with these constraints. The answer to these new challenges comes from hardware-software co-design. Computer Architectures and System Software should interact through a well-defined interface, exchanging run-time information, monitoring application progress and needs, and enforcing resource management. The CAOS research group carries out research mainly on real time and high performance computing with the following objectives:. Skip to main content.


1. CS Operating Systems. Computer Science. Lecture 4, page 1. Computer Science. Last Class: OS and Computer Architecture. • CPU, memory, I/O devices,​.


Kernel (operating system)

Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Bhattacharjee and D.

Go to lesson schedule. Knowledge and understanding: students wiil learn the theory and practice to realize an algorithm in hardware, exploring a spectrum of options ranging from dedicated specialized devices to programs on a general-purpose processor; they will understand how a processor works and how an high-level program is translated into machine language and then executed; they will understand the organization of a computer system and of the operating systems running on it, with the related issues of correctness and efficiency. Capabilities to apply knowledge and understanding: the students will be able to design specialized hardware for simple algorithms; translate simple programs from an high-level specification to machine language; write shell scripts using system calls in C in the UNIX environment; manage an information system, especially for what the installation and maintenance of applications and resources is concerned. Computer Architecture.

Сьюзан с опаской посмотрела на связанного шифровальщика. Стратмор сидел на диване, небрежно положив берет-ту на колени. Вернувшись к терминалу Хейла, Сьюзан приступила к линейному поиску. Четвертая попытка тоже не дала результата. - Пока не везет.

Такой жирный. Крикливый, тучный, мерзкий немец! - Клушар заморгал, стараясь переменить положение, и, не обращая внимания на боль, продолжал: - Ну чистая скотина, килограмм сто двадцать, не меньше. Он вцепился в эту красотку так, словно боялся, что она сбежит, - и я бы ее отлично понял. Ей-ей. Обхватил ее своими ручищами.

Сьюзан стояла, завернувшись в мохнатое полотенце, не замечая, что вода капает на аккуратно сложенные веши, приготовленные накануне: шорты, свитер - на случай прохладных вечеров в горах, - новую ночную рубашку. Расстроенная, она подошла к шкафу, чтобы достать чистую блузку и юбку. Чрезвычайная ситуация.

 - Рыженькие. - Да, а как зовут вашего брата. Я скажу вам, кто его сегодня сопровождает, и мы сможем прислать ее к вам завтра. - Клаус Шмидт, - выпалил Беккер имя из старого учебника немецкого.

Шифры, перехваченные АНБ, вводились в ТРАНСТЕКСТ и через несколько минуты выплевывались из машины в виде открытого текста.

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The answer to these new challenges must come from hardware-software co- design. Computer Architectures (CA) and Operating Systems (OS).

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