4.3 I/O Organization and Multiprocessor
Last updated
Last updated
This section delves into Input/Output (I/O) organization and the functioning of multiprocessor systems. It covers peripheral devices, I/O modules, direct memory access (DMA), and the characteristics of multiprocessors along with their communication mechanisms.
Input/Output (I/O) refers to the communication between an information processing system (like a computer) and the external world, including peripherals such as keyboards, displays, storage devices, and network interfaces. The organization of I/O involves the I/O modules that act as intermediaries between the CPU and peripheral devices.
1.1 Peripheral Devices
Peripheral devices are hardware components that are external to the computer system but are essential for input or output operations. These include:
Input Devices: Devices like keyboards, mice, scanners, and microphones that allow data to enter the system.
Output Devices: Devices like printers, monitors, and speakers that allow the system to output data.
Storage Devices: Devices like hard drives, SSDs, optical drives, and USB drives that provide long-term data storage.
Each of these devices communicates with the computer system through an I/O module.
1.2 I/O Modules
An I/O module is a piece of hardware responsible for managing communication between the CPU and peripheral devices. It provides a set of interfaces through which data is transferred between the devices and memory. Key tasks of an I/O module include:
Data transfer: It handles the transfer of data between the CPU and peripheral devices.
Control and Status Register: I/O modules often have control and status registers to monitor device status and send control signals to the devices.
Interrupt handling: It helps handle interrupts from peripheral devices, signaling the CPU for attention when needed.
1.3 Direct Memory Access (DMA)
Direct Memory Access (DMA) is a method that allows peripheral devices to communicate directly with the system memory without involving the CPU for every data transfer operation. This improves the system's overall performance by offloading data transfer tasks from the CPU, allowing it to perform other operations in parallel.
Key characteristics of DMA:
DMA Controller: The DMA controller manages the data transfer between I/O devices and memory. It coordinates the transfer, enabling peripherals to write data directly into memory.
DMA Channels: DMA uses specific channels for each device, allowing multiple peripherals to perform I/O operations concurrently without interfering with each other.
Data Transfer Process:
The CPU sends a request to the DMA controller for data transfer.
The DMA controller takes control of the system bus and performs the data transfer.
Once the transfer is complete, the DMA controller interrupts the CPU to notify it.
DMA enables high-speed data transfer, which is particularly useful for applications like disk transfers, audio/video streaming, and network communication.
A multiprocessor system is a computer system that has more than one processor (CPU). These systems are used to increase processing power, enhance performance, and support tasks requiring parallel computing. There are two primary types of multiprocessor systems: Tightly Coupled Systems and Loosely Coupled Systems.
2.1 Characteristics of Multiprocessors
Parallelism: Multiprocessors can execute multiple tasks simultaneously. This parallelism can be exploited for complex computational problems, allowing faster processing and increased system throughput.
Shared Memory: In a tightly coupled multiprocessor system, processors typically share a common memory. This enables efficient communication between processors, but it may also result in memory contention.
Multiple CPUs: A multiprocessor system can use multiple CPUs to perform parallel execution of programs, improving the system’s throughput and reducing processing time.
Reliability: Multiprocessor systems are more reliable because the failure of one processor does not bring down the entire system. Redundancy is built-in, and tasks can be redistributed to the remaining processors.
2.2 Types of Multiprocessor Systems
Symmetric Multiprocessing (SMP): All processors in an SMP system have equal access to the shared memory, and they work together to perform tasks. The operating system typically manages the workload across processors.
Asymmetric Multiprocessing (AMP): One processor (master) controls the system, while others (slaves) work on specific tasks. The master processor manages the memory and I/O, while the slave processors handle computation tasks.
Clustered Multiprocessing: Multiple processors are grouped into clusters, each with its own local memory. Communication between clusters is handled through high-speed interconnects.
2.3 Inter-Processor Communication
In a multiprocessor system, inter-processor communication is essential for coordinating tasks between processors and sharing data. This can be achieved through:
Shared Memory: Multiple processors access the same physical memory, enabling data sharing and synchronization. However, this can lead to issues like cache coherence and memory contention.
Message Passing: Processors communicate by sending messages to each other. This can be done over a network of processors (in a distributed system) or via a high-speed interconnect. Message passing is often used in distributed systems where memory is not shared, and processors are located in different physical locations.
Synchronization: Mechanisms like locks, semantics, and barriers are used to ensure that processors can safely share data and resources without causing conflicts.
I/O Organization: The organization of I/O involves peripheral devices, I/O modules, and DMA for efficient data transfer. I/O modules control data exchange between the CPU and external devices, while DMA allows direct memory access for faster transfers.
Multiprocessor Systems: Multiprocessor systems improve computational power by utilizing multiple processors. These systems can be classified as symmetric or asymmetric, depending on how the processors interact with each other. Efficient inter-processor communication through shared memory or message passing is key to their functionality.
