Peripheral Devices

Peripheral devices are input or output devices connected to a computer. These devices facilitate the transfer of information into or out of the computer’s memory under the control of the CPU and are considered part of the computer system. They are commonly referred to as peripherals.

1. Input Peripherals:

• Purpose: These devices allow users to input data or commands into the computer.Examples:
  • Keyboard: Used for typing text and issuing commands.
  • Mouse: Used for pointing, clicking, and navigating graphical user interfaces.
  • Scanner: Converts physical documents into digital images.
  • Microphone: Captures audio input, often used for voice recognition or recording.
  • Webcam: Captures video input, commonly used for video conferencing.

2. Output Peripherals:

• Purpose: These devices display or output data from the computer to the user.Examples:
  • Monitor/Display: Shows visual output such as text, images, and videos.
  • Printer: Produces physical copies of digital documents.
  • Speakers: Output audio, such as music, sound effects, or voice.
  • Projector: Displays computer output on a larger screen or surface.

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  Interface in Computer Systems

  An interface is a shared boundary between two components of a computer system. It enables communication between these components by allowing them to connect and interact efficiently.

  Types of Interfaces

  Interfaces in a computer system are categorized into two types:

  1. CPU Interface – Facilitates communication between the CPU and other internal system components.
  2. I/O Interface – Manages communication between the CPU and external peripherals.
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Understanding the I/O Interface

Peripherals connected to a computer require special communication links to interact with the CPU. In a computer system, special hardware components exist between the CPU and peripherals to manage input-output transfers. These components are known as input-output (I/O) interface units because they establish communication links between the processor bus and peripheral devices.

Functions of the I/O Interface

• Acts as a bridge between the internal system and external input-output devices.
• Controls and manages data transfer between the CPU and peripherals.
• Ensures smooth and efficient communication between system components.

Modes or Techniques of I/O Data Transfer

In a computer system, data transfer between the CPU and peripheral devices occurs through various techniques. These techniques ensure efficient communication and processing of data. The main modes of I/O data transfer are:

1. Programmed I/O

• In this method, the CPU directly controls the data transfer between itself and the peripheral devices.
• The CPU continuously checks the status of the I/O device (polling) and performs the data transfer when the device is ready.
• It is a simple but inefficient method because the CPU remains busy checking the device status.
• Example: Reading data from a keyboard or writing to a display screen.

2. Interrupt-Driven I/O

• Instead of continuously checking the device status, the CPU is notified by an interrupt signal when the device is ready for data transfer.
• The CPU can perform other tasks while waiting for an interrupt, improving efficiency.
• When an interrupt occurs, the CPU temporarily pauses its current task, handles the I/O request, and then resumes its previous operation.
• Example: A printer sending an interrupt signal to the CPU when it is ready to receive more data.

3. Direct Memory Access (DMA)

• In DMA, a special hardware component called the DMA controller handles data transfer between memory and I/O devices without CPU intervention.
• The CPU only initiates the transfer, and the DMA controller takes over the process, allowing the CPU to perform other tasks simultaneously.
• This technique significantly improves system performance, especially for large data transfers.
• Example: Transferring data from a hard drive to RAM.

The DMA (Direct Memory Access) Controller is a specialized hardware component that facilitates high-speed data transfer between I/O devices and memory without continuous intervention from the CPU. It acts as an interface between the data bus, memory, and I/O devices, allowing the CPU to delegate data transfer tasks and focus on other operations.

Block Diagram of a DMA Controller

Below is a simplified block diagram of a DMA Controller and its key components:

1. Control logic:
   • Manages the overall operation of the DMA controller.
   • Communicates with the CPU and I/O devices to initiate and control data transfers.
   • Handles signals like DMA Request (DRQ) and DMA Acknowledge (DACK).
2. Address Register:
   • Generates memory addresses for data transfer.
   • Selects the appropriate I/O device and memory location for reading or writing data.
   • Contains registers to store the starting address and address increment values.
3. Data Register:
   • Temporarily stores data during transfer between the I/O device and memory.
   • Acts as a bridge to compensate for speed differences between devices.

Block Diagram Of I/O Processor

• The diagram below shows a computer with different I/O processors. The memory unit is in the center and can communicate with all the processors. The CPU handles the data needed for calculations. The I/O processor (IOP) helps transfer data between the peripheral devices and memory. The CPU starts the I/O program, but the IOP works independently to move data between the devices and memory.

• The way the I/O processor (IOP) communicates with the devices is similar to the program control method of data transfer. Meanwhile, the communication between the IOP and memory is similar to the direct memory access (DMA) method.
• In large computers, each processor works independently, and any processor can start an operation. The CPU acts as the master, while the I/O processor (IOP) acts as the slave. The CPU is responsible for starting operations, but it is the IOP that actually executes the instructions, not the CPU. The CPU gives commands to begin an I/O transfer, and the IOP signals the CPU through an interrupt when it needs attention.
• The instructions that the I/O processor (IOP) reads from memory are called commands, to differentiate them from the instructions the CPU reads. These commands are created by programmers and stored in memory. The command words form the program for the IOP. The CPU tells the IOP where to find these commands in memory.

I/O Ports

An I/O port is a connection point that serves as an interface between the computer and external devices like a mouse, printer, modem, etc. There are two types of ports:

• Internal Port: This connects the motherboard to internal devices like a hard disk drive, CD drive, internal modem, etc.
• External Port: This connects the motherboard to external devices like a modem, mouse, printer, flash drives, etc.

Now, let’s look at some of the most commonly used ports:

Serial Port

Serial ports send data one bit at a time, which means they need only one wire to transmit 8 bits of data. However, this also makes them slower. Serial ports typically have 9-pin or 25-pin male connectors and are also known as COM (communication) ports or RS232C ports. Devices that use serial port connections include flat-screen monitors, GPS receivers, barcode scanners, and satellite phones or modems.

Parallel Port

Parallel ports can send or receive 8 bits (1 byte) of data at a time. These ports usually have 25-pin female connectors and are commonly used to connect devices like printers, scanners, and external hard disk drives.

Difference between Serial Ports and Parallel Ports

USB Port

USB stands for Universal Serial Bus. It is the industry standard for short-distance digital data connection. A USB port is used to connect various devices like printers, cameras, keyboards, speakers, and more. It was designed to standardize the connection of peripherals to personal computers, providing both communication and power supply.

USB has largely replaced older interfaces like serial and parallel ports and has become widely used across various devices.

USB Versions

There are several versions of USB, each with different data transfer speeds:

• USB 3.1: Known as Superspeed+, it can transfer data at a rate of 10 Gbps (10,240 Mbps).
• USB 3.0: Known as SuperSpeed USB, it can transfer data at up to 5 Gbps (5,120 Mbps).
• USB 2.0: Known as High-Speed USB, it has a maximum data transfer rate of 480 Mbps.
• USB 1.1: Known as Full Speed USB, it has a data transfer rate of 12 Mbps.

HDMI Ports

HDMI stands for High-Definition Multimedia Interface. It is a digital interface used to transmit both audio and video signals through a single cable. HDMI is commonly used with modern audio and video devices like 4K TVs, HDTVs, audio receivers, DVD/Blu-ray players, cable boxes, and video game consoles.

Unlike older audio/video connections, which require separate cables for audio and video, HDMI combines both into one cable, reducing cable clutter. For example, an analog connection may need five cables, but HDMI uses only one to transmit the same information.

VGA Ports

VGA stands for Video Graphics Array. It is the standard connection used for monitors and displays on most PCs. VGA-compatible monitors should work with most new computers. Developed by IBM in 1987, the VGA standard initially supported a resolution of 640×480 pixels. Over time, many revisions have been introduced, with Super VGA (SVGA) being the most common, allowing resolutions such as 800×600 or 1024×768.

A typical VGA connection has 15 pins and is shaped like a trapezoid.