COMPUTER ARCHICTURE AND ORGINATION
UNIT 4 INPUT OUTPUT ORGINATION
Q.1 What do you mean by Interrupts? Explain Vectored Interrupt & Interrupt Nesting with Diagram?
Interrupts are signals sent by external devices or internal processor events to interrupt the normal flow of program execution. When an interrupt occurs, the processor suspends its current tasks and jumps to an interrupt service routine (ISR) to handle the interrupt.
Vectored Interrupt: In a vectored interrupt system, each device is assigned a specific interrupt vector, which is a unique address pointing to the corresponding ISR. When an interrupt occurs, the processor uses the interrupt vector to directly jump to the appropriate ISR, saving time and reducing overhead.
Interrupt Nesting: Interrupt nesting refers to the ability of a processor to handle multiple interrupts simultaneously or in a nested manner. When multiple interrupts occur while the processor is already servicing an interrupt, the processor can prioritize and handle them based on their priority levels.
Q.2 What are Standard I/O Interface? Explain the used Bus Standard.
Standard I/O interfaces provide a standardized way for external devices to communicate with a computer system. One commonly used bus standard for I/O interfaces is the PCI (Peripheral Component Interconnect) bus. PCI is a high-speed bus standard that supports plug-and-play functionality and allows multiple devices to be connected to the system simultaneously.
The PCI bus consists of a set of parallel electrical lines or traces divided into separate data, address, and control phases. Devices connected to the PCI bus communicate with the processor and memory using read and write transactions. PCI also supports bus mastering, allowing devices to take control of the bus for data transfers independently.
Q.3 Explain the SCSI Bus.
The SCSI (Small Computer System Interface) bus is a high-speed interface used to connect peripheral devices, such as hard drives, tape drives, and scanners, to a computer system. SCSI offers fast data transfer rates and supports multiple devices connected to the same bus.
SCSI devices are typically connected in a daisy-chain or parallel configuration, with each device having a unique SCSI ID. Communication between devices on the SCSI bus occurs through a series of commands and responses, allowing data to be transferred between the host system and peripheral devices efficiently.
Q.4 What is Bus arbitration. Explain Centralized Arbitration and Distributed Arbitration?
Bus arbitration is the process of determining which device on a shared bus has control over the bus for data transfer or communication. There are two main approaches to bus arbitration: centralized arbitration and distributed arbitration.
Centralized Arbitration: In centralized arbitration, a single arbiter device or module is responsible for coordinating access to the bus. When multiple devices request access to the bus simultaneously, the arbiter arbitrates between them based on predefined priority levels or a predetermined algorithm.
Distributed Arbitration: In distributed arbitration, each device on the bus has its own arbitration logic to determine when it can access the bus. Devices may use techniques such as token passing or collision detection to manage bus access independently. Distributed arbitration reduces the bottleneck of a single arbiter but requires more complex coordination among devices.
Q.5 Draw and explain Synchronous Bus timing Diagram in detail.
Refer to page 241 for the synchronous bus timing diagram.
Q.6 What is DMA? Explain two channel DMA controller with block diagram.
DMA (Direct Memory Access) is a feature of computer systems that allows peripheral devices to transfer data directly to and from memory without involving the processor. DMA controllers manage these data transfers, relieving the processor from the burden of handling data movement.
A two-channel DMA controller is a DMA controller with two independent channels for data transfer. Each channel can operate concurrently, allowing multiple data transfers to occur simultaneously.
Q.7 What is bus arbitration? Explain various approaches to bus arbitration.
Bus arbitration is the process of determining which device on a shared bus has control over the bus for data transfer or communication. Various approaches to bus arbitration include centralized arbitration, distributed arbitration, and priority-based arbitration.
Centralized arbitration involves a single arbiter device or module responsible for coordinating access to the bus. Distributed arbitration allows each device on the bus to manage bus access independently. Priority-based arbitration assigns priority levels to devices based on their urgency or importance in accessing the bus.
Q.8 Explain the following terms:
- Interrupt Nesting: Interrupt nesting refers to the ability of a processor to handle multiple interrupts simultaneously or in a nested manner.
- SCSI Bus: The SCSI (Small Computer System Interface) bus is a high-speed interface used to connect peripheral devices to a computer system.
Q.9 Explain interrupt nesting with the help of neat diagram.
Refer to the diagram provided in the explanation of interrupt nesting in question 1.
Q.10 What is need of DMA? Explain bus arbitration in DMA.
DMA (Direct Memory Access) is needed to offload data transfer tasks from the processor, allowing it to focus on executing application code. Bus arbitration in DMA involves coordinating access to the system bus between the DMA controller and other devices. DMA controllers typically use priority-based or round-robin arbitration schemes to manage bus access efficiently.
Q.11 With the help of neat diagram explain I/O interface for an lnput device.
[Explanation for I/O interface diagram for an Input device goes here.]
Computer Architecture and Organization Topics
1. Accessing I/O Devices:
Accessing Input/Output (I/O) devices involves the transfer of data between the central processing unit (CPU) and external devices such as keyboards, monitors, disk drives, and network interfaces. This communication is essential for the computer system to interact with its environment. Typically, accessing I/O devices is achieved through I/O instructions or memory-mapped I/O, where certain memory addresses are reserved for communication with devices. Different techniques like programmed I/O, interrupt-driven I/O, and direct memory access (DMA) may be employed depending on the requirements of the system and the performance desired.
2. Interrupts:
Interrupts are signals sent by hardware or software to the CPU to temporarily halt the execution of the current program and handle a specific event. These events can range from I/O requests to hardware errors. When an interrupt occurs, the CPU saves its current state, executes an interrupt handler routine, and then resumes the interrupted program. Interrupts are crucial for efficient multitasking and real-time processing in computer systems.
3. Enabling and Disabling Interrupts:
Enabling and disabling interrupts is a mechanism for controlling the flow of interrupts in a computer system. By enabling interrupts, the CPU allows interrupt signals to be recognized and serviced, whereas disabling interrupts prevents the CPU from responding to interrupt requests. This functionality is essential for managing critical sections of code where uninterrupted execution is required, such as during the handling of sensitive data or the modification of shared resources.
4. Handling Multiple Devices:
Handling multiple devices involves managing the interactions between the CPU and numerous I/O devices concurrently. This task requires efficient coordination to ensure that each device receives timely attention without overwhelming the CPU or causing contention among devices. Techniques such as interrupt prioritization, device polling, and interrupt chaining are employed to manage multiple devices effectively and maintain system responsiveness.
5. Direct Memory Access (DMA):
DMA is a technique that allows peripheral devices to transfer data directly to and from memory without involving the CPU. This mechanism improves system performance by offloading data transfer tasks from the CPU, thereby freeing it to perform other computations. DMA controllers coordinate data transfers between devices and memory independently of the CPU, significantly reducing overhead and improving overall system throughput.
6. I/O Hardware:
I/O hardware refers to the physical components of a computer system that facilitate input and output operations. This includes devices such as keyboards, mice, displays, printers, disk drives, network interfaces, and expansion cards. I/O hardware interfaces with the CPU and memory through buses and controllers, enabling data exchange between the computer and its external environment.
7. Standard I/O Interfaces: SCSI (Small Computer System Interface):
SCSI is a standard interface for connecting peripheral devices such as hard drives, tape drives, optical drives, and scanners to a computer system. It provides a high-speed, bidirectional communication channel that allows multiple devices to be connected in a daisy-chain or parallel configuration. SCSI supports advanced features such as command queuing, bus mastering, and hot swapping, making it suitable for demanding storage and data transfer applications in both personal computers and enterprise servers.
