Jawaharlal Nehru Technological University Hyderabad B.Tech IV INFORMATION THEORY AND CODING Previous Question Paper (July - 2021 - R16)

Data transmission in storage systems involves moving information between a host processor and a storage medium (such as a hard disk or flash memory). The process ensures data integrity, efficiency, and reliability through several stages.

The block diagram flow is as follows: Data Source -> Encoder/ECC Generator -> Channel/Storage Medium -> Decoder/ECC Checker -> Data Sink.

1. Data Source: The host system generates the raw data to be stored.
2. Encoder/ECC Generator: Error Correction Code (ECC) bits are appended to the data to detect and correct potential errors during storage or retrieval.
3. Storage Channel: The data is modulated and written to the physical storage medium.
4. Decoder/ECC Checker: Upon retrieval, the system reads the data and uses the ECC bits to verify integrity. If errors are detected, the decoder attempts to correct them.
5. Data Sink: The verified, error-free data is delivered back to the host system.

Errors in data transmission and storage are generally classified based on their duration and pattern of occurrence:

• Single-Bit Errors: These occur when only one bit in a data unit (a byte or character) is changed from 0 to 1 or vice versa. These are typically caused by isolated noise or interference.
• Burst Errors: These occur when two or more bits in a data unit are changed. These are more severe and are often caused by impulse noise, fading, or physical defects in the storage medium. The length of the burst is measured from the first corrupted bit to the last.
• Random Errors: These occur independently of each other due to thermal noise in the communication channel or storage electronics.
• Erasure Errors: These occur when the position of the corrupted bit is known, but its value is unknown. This is common in storage systems where the controller can identify a 'bad' sector or block.