Computer Engineering Articles - Page 29 of 37

A zombie process is a process whose execution is completed but it still has an entry in the process table. Zombie processes usually occur for child processes, as the parent process still needs to read its child’s exit status. Once this is done using the wait system call, the zombie process is eliminated from the process table. This is known as reaping the zombie process.A diagram that demonstrates the creation and termination of a zombie process is given as follows −Salient points of Zombie ProcessesSome of the salient points related to zombie processes are as follows −All the memory and ... Read More

Pulse code modulation (PCM) is a technique of digitally representing analog signals. It takes samples of the amplitude of the analog signal and changes it to binary data. PCM technique is used by codecs in telephone networks to convert analog signals in local loops to digital signals in the trunks, and reverse conversion at the receivers’ end. Operations in Pulse Code Modulation The operations in PCM technique involves operations at the transmitting end and the operations at the receiving end. Transmitting End − In the transmitting end, the analog signals are sampled, quantized and encoded. The codec samples the analog ... Read More

Analog Telephone Cores The early telephone networks had analog cores. Frequency division multiplexing (FDM) was used to transmit a number of voice signals over the single line. Twelve calls were multiplexed into a group. Five groups were multiplexed into a supergroup. Digital Telephone Cores The present telephone networks have digital cores. This requires that the analog signals in the local loops are converted to digital signals that are transmitted via the trunks. This is done by codec (coder decoder). Time division multiplexing (TDM) is used to multiplex digital signals in the trunks, since it can be entirely handled by digital ... Read More

Trunks Definition Trunks are a large-bandwidth communication channels connecting switching centres, forming the core of the telephone network. A trunk comprises of a cluster of broadcast frequencies that are suitable for long haul communication of many voice and data signals simultaneously. Features The characteristic features of a trunk are − They carry digital information as opposed to analog signals carried by local loops. They are designed for both voice and data transmission. They can carry millions of calls simultaneously over long distances. They have very high bandwidth. They generally comprise of a cluster of fiber optic cables bundled together ... Read More

Debugging is the process of finding the problems in a computer system and solving them. There are many different ways in which operating systems perform debugging. Some of these are −Log FilesThe log files record all the events that occur in an operating system. This is done by writing all the messages into a log file. There are different types of log files. Some of these are given as follows −Event LogsThese stores the records of all the events that occur in the execution of a system. This is done so that the activities of all the events can be ... Read More

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

A command interpreter allows the user to interact with a program using commands in the form of text lines. It was frequently used until the 1970’s. However, in modern times many command interpreters are replaced by graphical user interfaces and menu-driven interfaces.Purpose of Command InterpretersCommand interpreters serve many purposes and are more useful than graphical user interfaces in some cases. Details about these cases are given as follows −Command interpreters have a large range of commands and queries available for different operations. Also, it is much faster to type than to click as is done using graphical user interfaces..There are ... Read More

Solaris is a Unix based operating system that was developed by Sun Microsystems and after its acquisition by Oracle it is known as Oracle Solaris. It is known for its scalability and its innovative features such as DTrace, ZFS, Time Slider etc.Solaris KernelThe kernel is the core of the operating system as its main function is to manage the hardware by allocating resources appropriately. Solaris is a microkernel design and it is not possible to create a monolithic Solaris kernel.Booting the kernel from a local disk in Solaris can be done using the following steps −Loading the bootblockReading and loading ... 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

Secondary storage devices are non-volatile devices where the data is stored for long-term storage. Disks are the mainly used secondary storage devices. They provide the bulk of secondary storage in operating systems today.The main activity that is performed in secondary storage management is disk scheduling. There are many disk scheduling algorithms. However, the important ones are FCFS scheduling, SSTF scheduling, SCAN scheduling and LOOK scheduling.All the disk scheduling algorithms are explained using the following requests for the disk -10, 95, 23, 78, 80First Come First Served SchedulingIn first come first served scheduling, the requests are serviced in their coming order. ... Read More