Semiconductor Memories
What is Semiconductor Memories?
The property of a memory that determines whether it retains its stored information when power is removed. Volatile memories lose data; non-volatile memories retain it.
Key formula / rule: Memory Capacity
Key points
- Differentiate between various types of semiconductor memories (RAM, ROM, SRAM, DRAM, PROM, EPROM, EEPROM, Flash).
- Understand the basic working principles and characteristics of each memory type.
- Analyze the trade-offs between speed, density, cost, and power consumption for different memories.
- Calculate memory capacity and determine the number of address and data lines required for a given memory size.
Common exam trap
Confusing volatility: RAM is volatile, ROM is non-volatile.
Definitions
- Term
Volatility
- Meaning
The property of a memory that determines whether it retains its stored information when power is removed. Volatile memories lose data; non-volatile memories retain it.
- Term
Access Time
- Meaning
The time delay between the initiation of a memory read/write operation and the completion of that operation (i.e., data becoming available or written).
- Term
SRAM (Static RAM)
- Meaning
A type of RAM that uses latches (typically 6 transistors per bit) to store data. It is faster and does not require refreshing but is less dense and more expensive than DRAM.
- Term
DRAM (Dynamic RAM)
- Meaning
A type of RAM that uses capacitors to store data (typically 1 transistor and 1 capacitor per bit). It is denser and cheaper than SRAM but slower and requires periodic refreshing to prevent data loss.
- Term
ROM (Read Only Memory)
- Meaning
A non-volatile memory that retains its data even without power. It is primarily used for reading data, though some types can be programmed or reprogrammed.
- Term
Flash Memory
- Meaning
A non-volatile EEPROM type memory that can be electrically erased and reprogrammed in blocks rather than individual bytes. It offers high density and is widely used in SSDs and portable devices.
Learning objectives
Differentiate between various types of semiconductor memories (RAM, ROM, SRAM, DRAM, PROM, EPROM, EEPROM, Flash).
Understand the basic working principles and characteristics of each memory type.
Analyze the trade-offs between speed, density, cost, and power consumption for different memories.
Calculate memory capacity and determine the number of address and data lines required for a given memory size.
Identify suitable memory types for specific applications.
Formulae
- Name
Memory Capacity
- Note
Total number of bits a memory can store.
- Expression
Capacity = Number of Words × Word Size
- Name
Number of Words from Address Lines
- Note
Where 'n' is the number of address lines. Each word is uniquely addressable.
- Expression
Number of Words = 2n
Prerequisites
Basic understanding of digital logic gates (AND, OR, NOT, XOR)
Knowledge of flip-flops and latches
Concepts of combinational and sequential circuits
Binary number system and data representation
Common mistakes
Confusing volatility: RAM is volatile, ROM is non-volatile.
Misunderstanding the refresh requirement: Only DRAM needs periodic refreshing.
Interchanging SRAM and DRAM characteristics regarding speed, density, and cost.
Not distinguishing between different ROM types based on their programming and erasing mechanisms.
Incorrectly calculating memory capacity or required address/data lines.
Keywords
Semiconductor Memory
RAM
ROM
Volatile
Non-volatile
SRAM
DRAM
PROM
EPROM
EEPROM
Flash Memory
Access Time
Memory Capacity
Address Lines
Data Lines
Practice preview
Which of the following is a volatile semiconductor memory?…
easy
Which type of semiconductor memory is typically used for storing the BIOS (Basic Input/Output System) in a computer?…
medium
A 16-bit memory chip has a word length of 16 bits and requires 12 address lines. How many memory locations does this chip have?…
medium