Ports & interfaces (Cambridge (CIE) AS Computer Science): Revision Note

USB

What is USB?

• The Universal Serial Bus (USB) is a widely used standard for transmitting data between devices

• It is a serial communication method (1 bit is transferred at a time), and it can be synchronous or asynchronous

• Many devices use USB such as:

  • Keyboards

  • Mice

  • Video cameras

  • Printers

  • Portable media players

  • Mobile phone

  • Disk drives

  • Network adapters

• Different USB connector types exist for different devices

• The letters refer to the physical shape and design of the USB connector:

  • USB-A - Commonly used for flash drives, mice, keyboards, external HDD

  • USB-B - Found in printers, scanners, and older external storage devices

  • USB-C - Latest standard, known for it's small size, transfer speeds, and it's ability to carry power

• The term USB can also be followed by numbers (USB 2.0, 3.0, 4 etc.)

• The numbers refer to the generation of USB technology, which determines the speed and performance:

  • USB 1.1 - 12 Mbps (very slow)

  • USB 2.0 - 480 Mbps (very common but slower compared to modern versions)

  • USB 3.0/3.1/3.2 - 5 Gbps to 20 Gbps (much faster, used for external HDDs and gaming devices)

  • USB4/ USB4 2.0 - Up to 80 Gbps (the latest and fastest, used for high speed data transfer)

• When a device is connected to a USB port the computer:

  • Automatically detects that the device has been connected

  • Looks for the correct driver:

    • If the driver is already installed, the appropriate device driver is loaded so that the device can communicate with the computer

    • If the device is new, the computer will look for a compatible device driver

    • If one cannot be found, the user must download and install an appropriate driver manually

Advantages and disadvantages of USB

HDMI

What is HDMI?

• HDMI is a digital port that sends both video and audio output from a computer to HDMI-enabled devices (e.g. TVs, monitors)

• Replaces older VGA analogue systems

• Modern HD TVs and displays require more data because they support:

  • Widescreen format (16:9 aspect ratio)

  • Higher resolution (e.g. 1920 × 1080 pixels)

  • Faster refresh rates (e.g. 120 Hz)

  • Wider colour range (millions of colour variations)

• These features need faster data transfer rates, which HDMI provides

• HDMI is a digital interface, so the signal does not need converting to analogue and back, and it is less prone to interference than VGA

• HDMI carries video and audio on the same cable, so no separate sound cable is needed

VGA

What is VGA?

• VGA (Video Graphics Array) is an analogue video port, introduced in the late 1980s, used to connect a computer to a monitor or projector

• It is now considered outdated and is being replaced by HDMI

• VGA carries video only, so a separate cable is needed for sound

• VGA has lower data transfer rates than HDMI, so it is less suited to high-resolution monitors

• VGA is an analogue signal, which means:

• The computer's digital data must be converted to analogue and back, so some data can be lost

• Lower image quality over long cables

• More likely to experience signal loss or interference