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SRAM (Static RAM):
Definition: A volatile memory (loses data when powered off) that offers very fast access times (in nanoseconds) due to its latch-based design.
Composition: Uses transistors arranged in a six-transistor latch circuit to store each bit.
Advantages: Faster access times, no refresh needed, lower power consumption for reads.
Disadvantages: More expensive per bit, lower density (less storage capacity per unit area), higher power consumption for writes
Usage: Cache memory, CPU registers, small, high-speed buffers.
DRAM (Dynamic RAM):
Definition: A volatile memory with slower access times (in tens of nanoseconds) but higher density (more storage capacity per unit area) compared to SRAM. Requires periodic refresh cycles to maintain data integrity.
Composition: Uses capacitors and transistors to store each bit. Capacitors hold the charge representing the data, and transistors act as switches to control access.
Advantages: Less expensive per bit, higher density, lower power consumption for writes.
Disadvantages: Slower access times, requires refresh cycles (increases power consumption), higher power consumption for reads.
Usage: Main memory (RAM) in computers.
Basic Concept of Memories
Memories are integrated circuits (ICs) designed to store data in a digital form (0s and 1s). They consist of a series of storage cells, each capable of holding a single bit. These cells are organized into a grid or matrix, allowing for efficient access using addresses.
Composition of Memories
Memories are typically composed of:
Storage cells: These hold the actual data bits (e.g., transistors and capacitors in SRAM and DRAM).
Decoders: Translate the address signals into control signals that select the specific storage cell to be read from or written to.
Sense amplifiers: (In SRAM) Boost weak signals read from storage cells to stronger levels for reliable detection.
Data buffers: Temporary storage locations for data during read or write operations.
Control circuitry: Manages data flow, refresh cycles (for DRAM), and error correction (if applicable).
Memory with Larger Word Size
Word size refers to the number of bits that can be accessed or transferred simultaneously in a memory operation. To create a memory with a larger word size, multiple memory chips with smaller word sizes can be combined in parallel.
Example: Constructing a 256 x 8 RAM using 64 x 8 RAM Modules.
Here's how you can construct a 256 x 8 RAM (memory with 256 words, each word being 8 bits wide) using four 64 x 8 RAM modules (each module has 64 words, each word being 8 bits wide):
Address Lines: You'll need 8 address lines (2^8 = 256) to select one of the 256 possible words in the combined memory. The upper 6 address lines will be used to select one of the four 64 x 8 modules, and the lower 2 address lines will be used to select one of the 8 words within the chosen module.
Data Lines: The data lines will remain 8 (representing the 8-bit word size). Each of the four 64 x 8 modules will connect its 8 data lines to the overall data lines of the combined memory.
Chip Enable (CE) Lines: Each 64 x 8 module will have its own chip enable line. To access a specific word, the corresponding module's CE line will be activated while the other modules' CE lines will be deactivated.
FIFO (First-In, First-Out) Memory
A FIFO is a type of sequential access memory that operates on the principle of "first-in, first-out" (FIFO). Data is written (inserted) at one end (the "input") and read (removed) from the other end (the "output"). It's like a queue, where the first element added is the first one to be removed.
Applications of FIFO:
· Buffering data streams between devices with different data rates.
· Implementing simple communication protocols.
· Implementing handshake mechanisms between components.