Ministry of Finance; Programmer Exam: 2013প্রশ্ন ও সমাধান

The Central Processing Unit (CPU) is the "brain" of the computer, executing instructions fetched from memory. It has three core components:

• Control Unit (CU): Fetches instructions from memory, decodes them, and generates control signals coordinating the ALU, memory, and I/O devices — it does not process data itself.
• Arithmetic Logic Unit (ALU): Performs all arithmetic (add, subtract, multiply) and logical (AND, OR, NOT, comparison) operations on data.
• Registers: Small, ultra-fast internal storage (Accumulator, Program Counter, Instruction Register) holding data/instructions currently in use.

graph TD
  IN[Input Unit] --> CPU
  subgraph CPU
    CU[Control Unit] <--> ALU[Arithmetic Logic Unit]
    CU <--> REG[(Registers)]
    ALU <--> REG
  end
  CPU --> OUT[Output Unit]
  CU <--> MEM[(Main Memory / RAM)]

Fetch-Decode-Execute cycle:

1. CU fetches the next instruction from main memory at the address held in the Program Counter.
2. CU decodes the opcode to determine the operation.
3. ALU executes the operation using operands from registers/memory.
4. The result is written back to a register or memory; the Program Counter advances to the next instruction.

Takeaway: CPU = Control Unit (coordinates) + ALU (computes) + Registers (fast local storage), all synchronized by the system clock in a repeating fetch-decode-execute cycle.

Database: An organized, persistent collection of related data, structured so it can be efficiently stored, retrieved, updated, and shared — typically managed through a DBMS (Database Management System, e.g. MySQL, Oracle, PostgreSQL) that provides controlled access, concurrency control, and recovery.

Importance of a database:

• Reduces redundancy — data is stored once and shared across applications instead of duplicated in separate files.
• Ensures integrity via constraints (primary key, foreign key, NOT NULL, CHECK).
• Enables concurrent multi-user access through transactions and locking (the ACID properties).
• Provides security through user- and role-level access control.
• Supports fast querying via SQL and indexing, unlike manually searching flat text files.
• Used for employee records, inventory, banking transactions, student records, etc.

Functions of a Database Administrator (DBA):

Function	Description
Schema design	Defines the conceptual, logical, and physical schema
Access control	Grants/revokes user privileges
Backup & recovery	Scheduled backups and disaster-recovery planning
Performance tuning	Monitors query performance, manages indexes
Integrity enforcement	Maintains constraints and validation rules
Physical storage design	Manages disk allocation and partitioning

Takeaway: A database is a managed data asset, not just "a file of data"; the DBA's core responsibility is keeping it available, consistent, secure, and fast.