A bootstrap program is the first code that is executed when the computer system is started. The entire operating system depends on the bootstrap program to work correctly as it loads the operating system.A figure that demonstrates the use of the bootstrap program is as follows −In the above image, the bootstrap program is a part of ROM which is the non-volatile memory. The operating system is loaded into the RAM by the bootstrap program after the start of the computer system. Then the operating system starts the device drivers.Bootstrapping ProcessThe bootstrapping process does not require any outside input to ... Read More

The interface between a process and an operating system is provided by system calls. In general, system calls are available as assembly language instructions. They are also included in the manuals used by the assembly level programmers. System calls are usually made when a process in user mode requires access to a resource. Then it requests the kernel to provide the resource via a system call.A figure representing the execution of the system call is given as follows −As can be seen from this diagram, the processes execute normally in the user mode until a system call interrupts this. Then ... Read More

Operating Systems have evolved over the years. So, their evolution through the years can be mapped using generations of operating systems. There are four generations of operating systems. These can be described as follows −The First Generation ( 1945 - 1955 ): Vacuum Tubes and PlugboardsDigital computers were not constructed until the second world war. Calculating engines with mechanical relays were built at that time. However, the mechanical relays were very slow and were later replaced with vacuum tubes. These machines were enormous but were still very slow.These early computers were designed, built and maintained by a single group of ... Read More

Many operating systems are not based on one model of the operating system. They may contain multiple operating systems that have different approaches to performance, security, usability needs etc. This is known as a hybrid operating system.The Hybrid operating system may allow one operating system to fulfil one set of requirements and the other operating system to fulfil the rest. For example, one of the operating systems may provide user interface, applications monitoring etc. while the other operating system may be a high-performance operating system that does not provide the same services as the first operating system.Features of Hybrid Operating ... Read More

The interface between a process and an operating system is provided by system calls. In general, system calls are available as assembly language instructions. They are also included in the manuals used by the assembly level programmers.Unix System CallsSystem calls in Unix are used for file system control, process control, interprocess communication etc. Access to the Unix kernel is only available through these system calls. Generally, system calls are similar to function calls, the only difference is that they remove the control from the user process.There are around 80 system calls in the Unix interface currently. Details about some of ... Read More

The GRUB (Grand Unified Bootloader) is a bootloader available from the GNU project. A bootloader is very important as it is impossible to start an operating system without it. It is the first program which starts when the program is switched on. The bootloader transfers the control to the operating system kernel. GRUB Features GRUB is the default bootloader for many of the Linux distributions. This is because it is better than many of the previous versions of the bootloaders. Some of its features are: GRUB supports LBA (Logical Block Addressing Mode) which puts the addressing conversion used ... Read More

The interface between a process and an operating system is provided by system calls. In general, system calls are available as assembly language instructions. They are also included in the manuals used by the assembly level programmers. System calls are usually made when a process in user mode requires access to a resource. Then it requests the kernel to provide the resource via a system calls.In general, system calls are required in the following situations −If a file system requires the creation or deletion of files. Reading and writing from files also require a system call.Creation and management of new ... Read More

The iOS is the operating system created by Apple Inc. for mobile devices. The iOS is used in many of the mobile devices for apple such as iPhone, iPod, iPad etc. The iOS is used a lot and only lags behind Android in terms of popularity.The iOS architecture is layered. It contains an intermediate layer between the applications and the hardware so they do not communicate directly. The lower layers in iOS provide the basic services and the higher layers provide the user interface and sophisticated graphics.The layered architecture of iOS is given as follows −Layers in iOS ArchitectureThe different ... Read More

The Erasable Programmable Read Only Memory is a memory chip that does not lose data even when the power is switched off. This is a non-volatile memory type i.e. it retains data even when the power is switched off. Each EPROM is individually programmed by an electronic device. After that, the data can be erased by exposing the EPROM to strong ultraviolet light.An EPROM contains a transparent fused quartz window at the top of the package which allows exposure to ultraviolet light. The silicon chip is visible from this window.EPROM OperationA single field effect transistor constitutes a storage location. This ... Read More

The Mac OS is a graphical operating system developed by Apple Inc. The tenth version of the Mac OS is the Mac OS X which was launched in 2001.The structure of the Mac OS X includes multiple layers. The base layer is Darwin which is the Unix core of the system. Next layer is the graphics system which contains Quartz, OpenGL and QuickTime. Then is the application layer which has four components, namely Classic, Carbon, Cocoa and Java. The top layer is Aqua, which is the user interface.A diagram that demonstrates the structure of Mac OS X is as follows ... Read More