Introduction to memory and memory units

Memory is an essential component of a computer system, responsible for storing data and instructions needed for processing. It enables the CPU to execute programs efficiently and ensures smooth system operation.

• Memory Cell: Smallest unit storing 1 bit of data with a unique address.
• Word & Byte: A word is a group of bits; 1 byte = 8 bits.
• Capacity: Total number of bits a memory can hold.

Classification of Memory

Memory is classified into primary and secondary types based on speed, accessibility, and volatility.

• Primary Memory: Directly accessible by the CPU; fast but limited in capacity.
• Secondary Memory: Used for long-term storage; slower but larger in capacity.

RAM (Random Access Memory)

RAM is the computer’s main memory used for temporary storage of active programs and data. Data is lost when power is off. It provides fast CPU access, improving multitasking and performance.

Types of RAM

• SRAM (Static RAM): Fast, used in cache, retains data while powered.
• DRAM (Dynamic RAM): Slower, needs periodic refresh; main memory. Includes SDRAM and DDR series.

Read more about this topic: Random Access Memory (RAM)

ROM (Read-Only Memory)

ROM is non-volatile memory that stores essential instructions permanently. It holds system firmware and boot instructions.

Types of ROM

Following are types of ROM:

• MROM: Pre-programmed at manufacture
• PROM: User-programmable once
• EPROM: UV-erasable
• EEPROM: Electrically erasable
• Flash Memory: Fast, used in SSDs and USB drives

Read more about this topic: Read Only Memory (ROM)

Secondary Memory

Secondary memory provides long-term data storage and is not directly accessed by the CPU.

• Examples: HDD, SSD, optical discs (CD/DVD/Blu-ray), USB drives, flash cards, magnetic tapes, cloud storage.
• Characteristics: Non-volatile, slower, high capacity, used for storing operating systems, software, and user files.

Read more about this topic: Secondary Memory

Differences Among RAM, ROM, and Secondary Memory

Following table shows major difference among three memory types:

Conversions of Units

The following table shows the standard conversions between different units of digital memory:

Suggested Quiz

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5 Questions

A memory that loses its contents when power is turned off and allows random access is:

• A

  ROM

• B

  DRAM

• C

  Flash Memory

• D

  PROM

Explanation:

DRAM is volatile, loses data without power, and allows random access. ROM and Flash are non-volatile

A memory type programmed only once during manufacturing is:

• A

  PROM

• B

  EPROM

• C

  EEPROM

• D

  SRAM

Explanation:

PROM can be programmed once and cannot be erased. EPROM and EEPROM can be reprogrammed. SRAM is volatile memory

Static RAM differs from dynamic RAM because:

• A

  SRAM is volatile, DRAM is non-volatile

• B

  SRAM stores data using flip-flops, DRAM uses capacitors

• C

  DRAM is faster than SRAM

• D

  SRAM is used in hard disks

Explanation:

SRAM uses bistable latches (flip-flops) and is faster, while DRAM uses capacitors and requires periodic refresh

Primary memory differs from secondary memory mainly in:

• A

  Access speed, volatility, and cost

• B

  Physical size and color

• C

  CPU instruction compatibility

• D

  Use in input/output devices

Explanation:

Primary memory (RAM, ROM) is faster and more expensive per bit, while secondary memory (HDD, SSD) is slower, non-volatile, and cheaper

A memory unit that can be electrically erased and reprogrammed multiple times is:

• A

  EPROM

• B

  MROM

• C

  EEPROM

• D

  DRAM

Explanation:

EEPROM allows electrical erasing and reprogramming, unlike EPROM which requires UV light for erasing

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