Understanding Computer Memory: Types, Features, and RAM

Understanding Computer Memory

Memory Types

Main Memory

Main memory is integrated into the system's firmware and directly governed by the CPU. It stores the boot process, data from the stack, memory-resident programs, and the user program currently executing.

Types of Main Memory:

• Ferrite memories (obsolete)
• Integrated memory:
  • RAM (Random Access Memory)
  • ROM (Read-Only Memory)
  • PROM (Programmable ROM)
  • EPROM (Erasable Programmable ROM)
  • OTP Memory (One-Time Programmable ROM)
  • EAROM (Electrically Alterable ROM)

Cache Memory

Cache memory is located within the CPU and communicates directly with it. It stores frequently used data to reduce access time from main memory.

Mass Memory

Mass memory refers to storage devices with higher capacity, typically peripherals.

Types of Mass Memory:

• Hard disk drives
• Floppy disk drives
• Optical disk drives
• Tape drives

Memory Features

Capacity

Capacity is the amount of information a memory unit can store, measured in bits. Multiples include:

• Byte: 8 bits
• Kilobyte (KB): 2¹⁰ bytes
• Megabyte (MB): 2²⁰ bytes
• Gigabyte (GB): 2³⁰ bytes

Access Time

Access time is the duration between requesting information from memory and receiving it.

Volatility

Volatility refers to a memory's ability to retain information when power is disconnected.

• Volatile Memory: (e.g., RAM) loses data without power.
• Non-Volatile Memory: (e.g., ROM) retains data without power.

Mode of Access

Mode of access is the method used to access stored information.

• Random Access
• Sequential Access
• Cyclic Access: (Combination of sequential and random access, used in hard disks and floppy disks)
• LIFO (Last In, First Out): Used for stack memory.
• FIFO (First In, First Out): The first element added is the first to be removed.

RAM (Random Access Memory)

Static RAM (SRAM)

SRAM is formed by flip-flops and is volatile.

Dynamic RAM (DRAM)

DRAM is formed by capacitors that store data. These capacitors require periodic refreshing, during which the memory cannot be accessed. DRAM offers higher capacity in less space compared to SRAM.

RAM with Battery

This type of RAM is non-volatile.