Question

Write a brief description of each of the following components. For IO Device Control Unit Buffer give a reason why useful/necessary.

1. System Bus

2. IO Device Control Unit

3. IO Device Control Unit Buffer

Answer 1

1. A bus is a bunch of wires used to connect multiple subsystems. Bus is a shared communication link for different devices. It allows easy addition of new devices and components in a system. Bus lines are divided into two types a) Control lines and b) Data lines. Control lines are used to control the information flow in the datalines between source and destination.

2. IO device Control unit is a unit responsible for handling the working of IO devices in a system. IO Device Control Unit receives the input and output requests from the central processor and send device-specific control signals to the device they control. The unit actually control the IO devices and thus relieves the cpu from the burden of controlling each IO device. Another key function of IO Device Control Unit is to convert the data which is read from input device or which is to be transferred to output device in appropriate form (human readeable to machine redeable and vice versa) .

3. IO Device Control Unit Buffer is a special kind of temporary storage for IO devices which is used to store sufficient amount of data before it is transferred to CPU. In a system, CPU communicates with the IO devices and vice versa and in order for a system to operate properly the devices must be in synchronization with the CPU. IO devices are usually slower than CPU e:g printer is slower than CPU and when CPU sends some data to be printed this data is stored in the buffer and then transferred to the printer with a speed suitable for printer. Similarly a buffer is used to temporarily store data being entered from a n input device like keyboard, which allows a large block of data to be keyed. held, and then transferred all at once to the CPU and in during the typing period CPU performs some other tasks. Benefits of IO Device Control Unit Buffer are

Flow Control. (Modules canbuffer data until the adjacent module is ready to receive it), Better CPU utiization, Better Throughput etc