Jawaharlal Nehru Technological University Hyderabad B.Tech II COMPUTER ORGANIZATION AND ARCHITECTURE Previous Question Paper (March - 2021 - R18)

A digital computer consists of five primary functional units that work together to process data:

1. Input Unit: Accepts raw data and instructions from external sources (e.g., keyboard, mouse) and converts them into a machine-readable binary format.
2. Memory Unit: Stores programs and data. It is divided into primary memory (RAM/ROM) for fast access by the CPU and secondary storage (HDD/SSD) for long-term data retention.
3. Arithmetic Logic Unit (ALU): Performs all arithmetic (addition, subtraction) and logical (AND, OR, NOT) operations required for data processing.
4. Control Unit (CU): Acts as the central nervous system of the computer. It coordinates the activities of all other units by issuing control signals, managing instruction execution, and controlling data flow.
5. Output Unit: Converts processed binary results into human-readable form (e.g., monitors, printers).

A common bus system allows multiple registers to transfer data to a single shared path using multiplexers to select which register's output is placed on the bus at any given time. For a system with n registers of k bits each, the construction involves:

1. Multiplexer Selection: Use k multiplexers, where each multiplexer has n inputs. Each input corresponds to the same bit position across all n registers.
2. Control Lines: The selection lines of all k multiplexers are tied together. A set of log2(n) control lines is used to select which register will output its data to the bus.
3. Data Routing: If register R0 is selected, the 0th input of every multiplexer is routed to its respective output, effectively placing the contents of R0 onto the bus lines.
4. Bus Width: The number of multiplexers used equals the word size (k bits), ensuring that all bits of the selected register are transferred in parallel.

This configuration prevents bus contention by ensuring only one register's output is enabled on the bus lines simultaneously.