1. Difference Between Serial and Parallel Transmission

   For transferring data between computers, laptops, two methods are used, namely, Serial Transmission and Parallel Transmission. There are some similarities and dissimilarities between them. One of the primary difference is that; in Serial Transmission, data is sent bit by bit whereas, in Parallel Transmission a byte (8 bits) or character is sent at a time.

2. Network Operating System

   Network Operating System is a computer operating system that facilitates to connect and communicate various autonomous computers over a network. An Autonomous computer is an independent computer that has its own local memory, hardware, and O.S. It is self capable to perform operations and processing for a single user. They can either run the same or different O.S.

3. Spooling

   Simultaneous peripheral operation online, acronym for this is Spooling. A spool is a kind of buffer that holds the jobs for a device till the device is ready to accept the job. Spooling considers disk as a huge buffer that can store as many jobs for the device till the output devices are ready to accept them. In spooling, I/O of one job is overlapped with the computation of another job. For example, a spooler at a time may read input of one job, and at the same time, it may also print the output of another job. Spooling can also process data at the remote sites. The spooler only has to notify when a process gets completed at the remote site so that spooler can spool next process to the remote side device. Spooling increases the performance of the system by increasing the working rate of the devices. It naturally leads to multiprogramming.

4. Buffering

   Before discussing buffering, let us discuss, what is the buffer? The buffer is an area in the main memory that is used to store or hold the data temporarily that is being transmitted either between two devices or between a device or an application. In simple words, buffer temporarily stores data that is being transmitted from one place to another. The act of storing data temporarily in the buffer is called buffering. There are three reasons behind buffering of data, first is it helps in matching speed between two devices, between which the data is transmitted. For example, a hard disk has to store the file received from the modem. Now, as we know the transmission speed of a modem is slow, as compared to the hard disk. So bytes coming from the modem is accumulated in the buffer space, and when all the bytes of a file has arrived at the buffer, the entire data is written to the hard disk in a single operation. Secondly, it helps the devices with different data transfer size to get adapted to each other. It helps devices to manipulate data before sending or receiving. In computer networking, the large message is fragmented into the small fragments and sent over the network. At the receiving end, the fragments are accumulated in the buffer and reassembled to form the complete large message. The third use of buffering is that it also supports copy semantics. With copy semantics, the version of data in the buffer is guaranteed to be the version of data at the time of system call irrespective of any subsequent change to data in the buffer. Buffering increases the performance of the device. It overlaps the i/o of one job with the computation of the same job.

5. I/O buffering and its Various Techniques

   A buffer is a memory area that stores data being transferred between two devices or between a device and an application. There are some types of buffering technique, single buffer, double buffer, and circular buffer. Each type has it’s own advantages and uses in some cases.

6. Direct Memory Access (DMA)

   Direct memory access (DMA) is a mode of data transfer between the memory and I/O devices. This happens without the involvement of the processor. We have two other methods of data transfer, programmed I/O and Interrupt driven I/O. Let’s revise each and get acknowledge with their drawbacks. In programmed I/O, the processor keeps on scanning whether any device is ready for data transfer. If an I/O device is ready, the processor fully dedicates itself in transferring the data between I/O and memory. It transfers data at a high rate, but it can’t get involved in any other activity during data transfer. This is the major drawback of programmed I/O. In Interrupt driven I/O, whenever the device is ready for data transfer, then it raises an interrupt to processor. Processor completes executing its ongoing instruction and saves its current state. It then switches to data transfer which causes a delay. Here, the processor doesn’t keep scanning for peripherals ready for data transfer. But, it is fully involved in the data transfer process. So, it is also not an effective way of data transfer.

7. Programmed I/O

   In this mode the data transfer is initiated by the instructions written in a computer program. An input instruction is required to store the data from the device to the CPU and a store instruction is required to transfer the data from the CPU to the device. Data transfer through this mode requires constant monitoring of the peripheral device by the CPU and also monitor the possibility of new transfer once the transfer has been initiated. Thus CPU stays in a loop until the I/O device indicates that it is ready for data transfer. Thus programmed I/O is a time consuming process that keeps the processor busy needlessly and leads to wastage of the CPU cycles. This can be overcome by the use of an interrupt facility. This forms the basis for the Interrupt Initiated I/O.

8. Interrupt Initiated I/O

   This mode uses an interrupt facility and special commands to inform the interface to issue the interrupt command when data becomes available and interface is ready for the data transfer. In the meantime CPU keeps on executing other tasks and need not check for the flag. When the flag is set, the interface is informed and an interrupt is initiated. This interrupt causes the CPU to deviate from what it is doing to respond to the I/O transfer. The CPU responds to the signal by storing the return address from the program counter (PC) into the memory stack and then branches to service that processes the I/O request. After the transfer is complete, CPU returns to the previous task it was executing. The branch address of the service can be chosen in two ways known as vectored and non-vectored interrupt. In vectored interrupt, the source that interrupts, supplies the branch information to the CPU while in case of non-vectored interrupt the branch address is assigned to a fixed location in memory.

9. Difference between Maskable and Non Maskable Interrupt

   An interrupt is an event caused by a component other than the CPU. It indicates the CPU of an external event that requires immediate attention. Interrupts occur asynchronously. Maskable and non-maskable interrupts are two types of interrupts. An Interrupt that can be disabled or ignored by the instructions of CPU are called as Maskable Interrupt.The interrupts are either edge-triggered or level-triggered or level-triggered. An interrupt that cannot be disabled or ignored by the instructions of CPU are called as Non-Maskable Interrupt.A Non-maskable interrupt is often used when response time is critical or when an interrupt should never be disable during normal system operation. Such uses include reporting non-recoverable hardware errors, system debugging and profiling and handling of species cases like system resets.

10. Difference between Hardware Interrupt and Software Interrupt

    Hardware Interrupt is caused by some hardware device such as request to start an I/O, a hardware failure or something similar. Hardware interrupts were introduced as a way to avoid wasting the processor’s valuable time in polling loops, waiting for external events. For example, when an I/O operation is completed such as reading some data into the computer from a tape drive. Software Interrupt is invoked by the use of INT instruction. This event immediately stops execution of the program and passes execution over to the INT handler. The INT handler is usually a part of the operating system and determines the action to be taken. It occurs when an application program terminates or requests certain services from the operating system. For example, output to the screen, execute file etc.