SRAM Full Form - Static Random Access Memory

Static Random Access Memory kind of volatile semiconductor memory, or simply SRAM, as it is called wide applications in computing and electronic devices. Its characteristics, advantages, disadvantages, and applications will be discussed.

In this article, the history of SRAM, its working architecture, and comparisons with other types of memory are elaborated to give a proper overview of this expensive yet fast memory technology.

What is SRAM?

SRAM stands for Static Random Access Memory. It is a form of a semiconductor. It is widely used in microprocessors, general computing applications, and electronic devices. The SRAM is volatile which means the data stored in it gets all wiped out once the power supply is cut. SRAM comprised of flip flops. It consists of 4-6 transistors, once the flip flop stores the bit it keeps it stored until the opposite bit is stored in it. 

History of SRAM

Engineer John Schmidt invented the SRAM in 1964 at Fairchild Semiconductors. The first SRAM is 64-bit and uses p-channel MOS. 

Intel released its first 256-bit Intel 1101 SRAM chip in 1969, five years after its invention. But it uses Schottky TTL (Transistor-Transistor-Logic) architecture for its build. 

Early SRAMs were manufactured using ceramic plastic. But nowadays, SRAMs are integrated directly to the CPU for faster and better processing.

Characteristics

• The data is held statically: The data is stored statically in SRAM and it doesn't need to be refreshed unlike DRAMs.
• It is a type of Random Access Memory: The SRAM is a type of Random Access Memory. Random Access Memories are those from which the data can be accessed (read/write) randomly (means any memory location can be accessed), regardless of the memory location that was accessed earlier.
• It uses flip flop for storing data: It uses flip flops to store bits. Each flip flop is made up of 4-6 transistors.
• It is used as a Cache Memory in CPU: SRAM is used as cache memory for CPUs as they are faster and stores data statically.

Advantages

• It is faster to access and perform operations like read & write.
• The data can be accessed randomly.
• It is used as a cache memory.
• It doesn't need to be refreshed as it stored data statically.
• It has medium power consumption. It requires less power as compared to DRAM.

Disadvantages

• It is expensive.
• It is volatile in nature i.e., data is lost when the memory is not powered.
• It has a low storage capacity.
• It is not possible to refresh the program.
• It has a more complex design and they are bigger in size as well when compared to DRAM.
• It reduces the memory density.

Examples of SRAM

1. Cache memory:

• L1, L2, and L3 cache in CPUs
• Cache in GPUs

2. Register files in microprocessors

3. Small amounts of memory in microcontrollers

Working Architecture of One Bit SRAM

One-bit SRAM cell typically consists of six transistors arranged in a specific configuration. Here's a basic explanation of its components and operation:

Core storage element:

• Two cross-coupled inverters (4 transistors total)
• They form a latch that can store either a 0 or 1

Access transistors:

• Two additional transistors
• Used to read from or write to the cell

Bit lines:

• Two lines (BL and BL')
• Used for reading and writing data

Word line:

• One line (WL)
• Used to activate the access transistors

Operation:

• To write: The desired value is placed on the bit lines, and the word line is activated.
• To read: The word line is activated, and the stored value affects the bit lines.

Conclusion

The most volatile semiconductor memory prevailing in every computing and electronic device is called SRAM, or Static Random Access Memory. In the year 1964, John Schmidt invented this SRAM. Flip-flops have 4-6 transistors which store the data statically in a cell and hence do not require refresh cycles to hold the data. The key properties of SRAM are that it has faster access times, provides random data access, and uses CPU cache memory.

But at the same time, while SRAM has its speed advantages and is even more power-efficient than DRAM, the cons of using it are higher cost, lower storage capacity, volatility. It finds applications in CPU cache memory, GPU cache, microprocessor register files, and microcontrollers. One standard architecture in SRAM will contain six transistors, forming a storage cell with access transistors and bit/word lines for the operations of read/write.