Computer Memory Unit II

Computer Memory

• Memory functions similarly to the human brain, storing data and instructions required for processing.
• Organized in multiple small parts called cells, each with a unique address ranging from 0 to memory size minus one.
• For example, 64k words of memory provide 65536 memory locations (addresses 0 to 65535).

Types of Memory

• Three primary types:
  • Cache Memory
  • Primary Memory (Main Memory)
  • Secondary Memory

Cache Memory

• High-speed semiconductor memory that enhances CPU performance.
• Acts as a buffer, holding frequently used data and programs.
• Data is transferred to cache from disk via the operating system for quicker CPU access.

Advantages

• Faster access than main memory.
• Reduces access time significantly.
• Temporarily stores executables for efficient processing.

Disadvantages

• Limited storage capacity.
• Expensive compared to other memory types.

Primary Memory (Main Memory)

• Holds data and instructions currently being processed.
• Limited capacity and volatile; data is lost when power is off.
• Composed of semiconductor devices, operating faster than secondary memory.
• Further divided into RAM (Random Access Memory) and ROM (Read-Only Memory).

Characteristics of Main Memory

• Semiconductor-based and usually volatile.
• Essential for the computation process.
• Faster than secondary storage, but data is lost if power is interrupted.

Secondary Memory

• Also known as external or non-volatile memory; slower than primary memory.
• Stores data permanently and accessed via input-output routines.
• CPU indirectly accesses secondary memory by first loading contents into primary memory.
• Examples include hard drives, CD-ROMs, and DVDs.

Characteristics of Secondary Memory

• Magnetic and optical storage media.
• Non-volatile, data remains even after power is switched off.
• Acts as backup storage; a computer can operate without it.
• Slower than primary memory.

Memory Unit

• Random Access Memory (RAM) temporarily stores information for efficient processing.
• Storage drives retain data permanently, with capacity expressed in Bytes.

Basic Units of Memory

• Bit: The smallest unit of data, a binary digit (0 or 1).
• Nibble: Group of 4 bits.
• Byte: Group of 8 bits, smallest unit that can represent a data item or character.
• Word: Group of bits processed as a unit, size varies by computer (8 to 96 bits).

Storage Capacity Units

• Kilobyte (KB): 1 KB = 1024 Bytes.
• Megabyte (MB): 1 MB = 1024 KB.
• Gigabyte (GB): 1 GB = 1024 MB.
• Terabyte (TB): 1 TB = 1024 GB.
• Petabyte (PB): 1 PB = 1024 TB.

Secondary Storage Device

• Also known as external memory or auxiliary storage; non-volatile, retains data until deleted or overwritten.
• Generally much cheaper than primary storage, facilitating larger data retention.

Dive into the fundamentals of computer memory in this quiz. Explore how memory functions similarly to the human brain, including its structure, storage cells, and addressing. Test your knowledge on how data and instructions are processed within a computer's memory.