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1. OSI (Open Systems Interconnection) Layers

1. It has been developed by ISO - "International Organization of Standardization", in 1974. It's a 7-layer architecture with each layer having specific functionality to perform. All these 7 layers work collaboratively to transmit the data from one person to another across the globe.

2. Layers of OSI

1. Physical Layer (Layer 1)

1. known as Hardware/Media layers

2. Data Link Layer (Layer 2)

1. known as Hardware/Media layers

3. Network Layer (Layer 3)

1. known as Hardware/Media layers

4. Transport Layer (Layer 4)

1. Heart of OSI

5. Session Layer (Layer 5)

1. known as Software/Host layers

6. Presentation Layer (Layer 6)

1. also called the "Translation Layer"

2. known as Software/Host layers

7. Application Layer (Layer 7)

1. known as Software/Host layers

2. ACID Properties in a Database

1. Atomicity

1. Atomicity ensures that a transaction is treated as a single, indivisible unit of work. Transactions are either completed in their entirety or not at all. If any part of a transaction fails, the entire transaction is rolled back, and the database remains unchanged. 

2. Consistency

1. Transactions never leave your database in a half-finished state

3. Isolation

1. Keeps transactions separated from each other until they have finished 

4. Durability

1. Keep track of pending changes

3.  Deadlock

1. A deadlock is a situation that occurs in a concurrent system, such as a computer program or a database, where two or more processes (or threads) are unable to proceed because each is waiting for a resource that the other holds.

2. There are four necessary conditions for a deadlock to occur, often referred to as the "deadlock conditions" or the "Coffman conditions":

1. Mutual Exclusion

2. Hold and Wait

3. No Preemption

4. Circular Wait

3. Types of deadlocks

1. Cycle locks deadlock

2. Conversion locks deadlock

4. Deadlock Prevention

1. Wait-Die Scheme

2. Wound Wait Scheme 

3. Resource Allocation Graph

4. Lock Ordering

5. Timeouts

6. Resource Preemption

7. Process Termination

8. Avoidance Algorithms

9. Distributed Systems and Database Management

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