An In-Depth Comparison of SRAM vs DRAM Technology

Random access memory (RAM) comes in two major varieties—static RAM (SRAM) and dynamic RAM (DRAM). Both act as temporary data stores for devices like computers and mobile gadgets. But they differ greatly when it comes to speed, cost, complexity and other key parameters.

This guide will delve into all you need to know about SRAM and DRAM, highlighting their respective strengths and explaining where each excels. You‘ll learn:

• How both RAM types temporarily store data
• Their history and origins
• Speed, cost and capacity differences
• Which applications they are best suited for

Let‘s start by examining what exactly SRAM and DRAM are.

What is Static RAM (SRAM)?

First developed in the early 1960s, static RAM uses a type of flip-flop circuit technology to store data bits. This grants SRAM faster access speeds compared to DRAM.

The term static refers to how SRAM cells maintain data indefinitely, for as long as power remains on. This removes any need to refresh stored values, contributing to SRAM‘s performance edge.

What is Dynamic RAM (DRAM)?

Dynamic RAM, first introduced commercially in the early 1970s, relies on a radically different cell design. Each bit resides in a storage cell composed of one capacitor and one access transistor rather than SRAM‘s 6 transistors.

The term dynamic references how the charge in DRAM capacitors leaks away over time. So the memory controller must periodically refresh the charge to keep data intact.

While the simple DRAM cell enables huge densities, the refresh requirement causes slower speeds than SRAM. Next we‘ll examine the history behind both memory advances.

History and Origins

Both forms of RAM have origins tied to early semiconductor advancements of the 1960s:

1963 – Robert Norman files SRAM patent using new bipolar transistor technology at Fairchild Semiconductor

1964 – Fairchild‘s John Schmidt proposes first MOS semiconductor SRAM cell

1966 – IBM‘s Dr Robert Dennard conceptualizes single-transistor DRAM cell combining both transistor and capacitor

DRAM took over a decade to materialize given initial manufacturing limitations. But by the 1970s and 80s DRAM‘s new MOSFET standard gained adoption across the booming electronics industry while new support standards helped ensure reliable operation.

Now powered by over 50 years of non-stop innovations, SRAM and DRAM satiate the world‘s growing hunger for faster, denser memory in nearly all computing devices. Next let‘s compare how they differ at a cellular level.

How SRAM and DRAM Store Data

Though both provide temporary data storage, SRAM and DRAM use very different grid-like arrays of memory cells to fulfill the task:

SRAM relies on four to six transistors to form a latching circuit capable of storing a bit indefinitely without leakage or fading. Additional control transistors route data in/out. So long as power applies, the latched state remains.

DRAM utilizes a radically simple cell requiring only one access transistor and one capacitor, total. The capacitor either holds or lacks a charge, corresponding to 1 or 0. But the charge leaks away and must be periodically restored via refresh cycles.

So in summary:

• SRAM: Fast static latch maintains data so long as circuit powered

• DRAM: Simple cell leaks charge and needs refresh cycles

Next let‘s quantify speed differences between SRAM and DRAM…

Speed and Latency Comparison

Due to its directly attached memory transistors requiring lower charge/discharge times, SRAM offers data access speeds less than 10 nanoseconds – over 10 times faster than DRAM. The chart below contrasts typical latencies:

Also, DRAM‘s required refresh cycles further reduce available bandwidth for data input/output. So for applications needing swift data delivery like cache, processor registers or other interim buffers, SRAM is clearly the superior choice.

However what about non-speed factors like cost? Keep reading to learn why DRAM dominates capacity needs…

Cost Per Bit Comparison

Given its simplistic cell, DRAM requires essentially 1/6th the circuitry per stored bit compared to SRAM. This translates into a per-bit-cost around 150 times less for DRAM! The table below summarizes typical relative expenses:

So while SRAM fits specialized roles where speed is paramount like cache, DRAM‘s cost efficiency makes it nearly universally ideal for maximizing memory capacity – be it on desktops, servers or mobile devices.

Density and Capacity Comparison

Given its transistors-and-capacitors-only makeup, DRAM‘s tiny cell size enables spectacular density advantages over SRAM. While SRAM may reach ~256 megabits per chip, DRAM can attain up to 512 gigabits per chip – a difference of 2000x!

This allows common DRAM module sizes ranging from megabytes up to terabytes. The table below summarizes typical capacities:

So if high capacity at minimal expense is required, as with system memory, hard drives or cloud servers, DRAM is nearly always the right pick over SRAM and other alternatives. We‘ll next examine their power consumption and volatility traits…

Power Consumption Comparison

Due to its simpler cell, DRAM inherently requires less active and standby power than SRAM to store each bit. However refresh cycles do consume additional energy relative to SRAM.

In turn, SRAM‘s faster performance leads to somewhat higher active power. But its static latch cell design does prevent any leakage or refresh current needs. The table below summarizes typical power needs:

So while neither option wins outright, DRAM often sees deployment in low power devices like phones and tablets where capacities needs preclude power-hungry SRAM. For nonstop operation like servers and networks, SRAM makes sense to eliminate refresh cycles.

Volatility Comparison

Volatility refers to how memory technologies retain data after power is cut off – like during a sudden reboot or failure.

SRAM offers perfect data persistence so long as powered on thanks to its static latch design. Yet once external power is interrupted, data vanishes instantly.

Conversely DRAM suffers degradation gradually as charge diffuses across powered-off cell capacitors. So data persists for up to seconds after cutting power, making DRAM non-volatile enough for quick shutdowns like Sleep modes. Adding backup batteries can extend retention further.

Lifetime and Reliability

Unlike early variations, modern DRAM coupled with sophisticated controllers achieves acceptable reliability over years of use. So expected lifetimes now differ little between most quality SRAM and DRAM products.

However for specialized roles like aerospace or medical gear needing decades of uninterrupted uptime, SRAM maintains an advantage given its simpler cell and lack of reliance on capacitance.

Common Applications

Given the above comparisons, SRAM and DRAM now dominate different computing niches:

SRAM matches roles where speed is fundamental and budget secondary:

• Processor cache memory
• Networking/infrastructure buffers
• Industrial controls

DRAM suits applications centered on maximizing capacity yet latency needs allow:

• Computer main system memory
• Smartphone/tablet storage
• Cloud storage arrays

High performance graphics and computing blending both – with SRAM handling time-sensitive tasks like texture maps while background DRAM provides abundant textures and data.

Now that you understand their core differences, let‘s conclude with some key takeaways…

Conclusion and Key Takeaways

• SRAM uses latching circuits to store data fast as long you power it on – while DRAM uses tiny capacitors that leak charge needing frequent refresh
• But DRAM‘s simple cell means it‘s over 150 times cheaper per bit than SRAM!
• SRAM thus dominates in processor cache and other speed-critical roles
• DRAM rules system memory and any application where massive, affordable capacity is fundamental

So in closing – both SRAM and DRAM will continue flourishing in computers for years to come. SRAM provides the speed to keep processors running full tilt, while DRAM delivers the mammoth capacities needed for ever expansive applications.

Understanding how these two technologies differ allows engineers to apply them optimally across the computing landscape – ensuring devices offer both swift responsiveness and abundant storage at reasonable costs.

Hopefully this guide shed insight on the SRAM vs DRAM decision for your next electronics project! Let me know if you have any other questions.