Random Access Memory (RAM) comes in various forms for different purposes. The main types are DRAM, SRAM, SDRAM, VRAM, and NVRAM. All these RAMs have further types, but we will focus on the main types. We will compare the DRAM (primary memory), SDRAM (primary memory synchronized with the system clock), SRAM (generally used in cache), and VRAM (Graphics Memory) in this article.
The data in the RAM can be accessed randomly in any order, unlike sequential storage. However, another key feature is that RAM loses its data when the power is turned off, except for other RAM variants, such as NVRAM and MRAM. The four types of RAM that we are discussing lose their data when the power is turned off, hence called volatile memory.
RAM is also known for its high bandwidth, throughput, and low latency. I have discussed the work of DRAM in complete detail in this article. In this article, we will know the purposes of these RAM types and their applications. So, let’s get started.
The purpose of RAM in devices
RAM (Random Access Memory) is an integral part of computers, laptops, smartphones, tablets, and all other devices that incorporate a CPU for their operations. RAM can be inside the CPU in the form of SRAM as a cache. It could be in your graphics card as VRAM. It could be the DRAM modules installed in your computer or laptop. It could be the LPDDR used in mobile devices because of its power efficiency. It could also be that the SDRAM is an external RAM, but it shares the CPU’s clock.
But the purpose is almost the same everywhere. RAM works in tandem with the CPU or GPU to provide high-speed memory for tasks at hand. It provides a perfect balance between low price, high storage capacity, and read/write performance. Now, RAM has numerous applications in various settings.
SRAM, for example, has the highest speed among all types of RAM, with the lowest latency. It is used in petite sizes due to its high price, as it is utilized in CPU caches and other high-speed buffers. After that, in terms of performance, come the GDDR and HMB memories, which are types of VRAM. This RAM is used in graphics cards. DRAM and SDRAM have lower speeds than the VRAM, which is used as the main memory, generally in the form of DIMM modules. So, RAM can have different purposes, and to accomplish them, manufacturers have made tweaks to the design to achieve the desired results.
1. What is DRAM (Dynamic Random Access Memory)
The word “Dynamic” in DRAM means that this RAM requires regular refreshing to retain its data. Dynamic RAM is called Dynamic in contrast to Static RAM, which doesn’t need refreshing. A single memory cell in DRAM is made up of a combination of a transistor and a capacitor.
The capacitor stores the bits in the form of electric charge. A charged capacitor represents the bit value of “1” while a discharged one represents “0”. However, capacitors have an inherent tendency to leak the stored charge just after they are charged slowly. So, if we don’t refresh it with the appropriate voltage, it will soon lose its data. The data is refreshed approximately every 64 milliseconds; however, it can vary depending on the RAM.
Purpose and Deployment of DRAM
DRAM is also known as Asynchronous Random Access Memory and is essentially obsolete, having been replaced by the modern SDRAM. Modern computers generally use the SDRAM, particularly DDR SDRAM. However, you can also refer to SDRAM as another type of DRAM. DRAM doesn’t synchronize with the CPU’s clock and has its own oscillator to generate the clock. Because of this separate clock, the CPU doesn’t align correctly in terms of clock frequency with the DRAM.
Types of DRAM
- Asynchronous DRAM (ASDRAM): The original form of DRAM that operates independently of the system clock. It is generally slower and has been largely replaced by synchronous types.
- Fast Page Mode DRAM (FPM DRAM): An enhancement over standard DRAM that allows faster access to data within the same row, improving performance compared to traditional asynchronous DRAM. However, generally not found in any modern systems.
- Extended Data Out DRAM (EDO DRAM): This type of DRAM allows for faster access than FPM by overlapping the next read cycle with the current one, thereby providing improved performance.
- Burst EDO DRAM: An extension of EDO DRAM that can deliver a burst of data quickly, further improving speed and efficiency.
- DDR SDRAM (Double Data Rate SDRAM): The most successful and scalable type of DRAM. This includes several generations (DDR, DDR2, DDR3, DDR4, DDR5, and the upcoming DDR6), allowing data to be transferred on both the rising and falling edges of the clock signal, effectively doubling the data rate.
- RLDRAM (Reduced Latency DRAM): A type of DRAM designed for applications that require low latency, often used in networking and telecommunications.
2. What is SDRAM?
As we discussed earlier, SDRAM is a type of DRAM memory and uses the same combination of a transistor and a capacitor for a single memory cell. However, the SDRAM comes with a much more complex and efficient caching and buffering mechanism compared to the standard DRAM. SDRAM can handle data in bursts and work with multiple data requests simultaneously.
You can refer to this paper from HP to gain a simpler understanding of SDRAM. According to it, “Standard DRAM transfers one data bit to the bus on the rising edge of the bus clock signal, while DDR SDRAM uses both the rising and falling edges of the clock to trigger the data transfer to the bus.”
However, if you want to know the workings of SDRAM in detail, this paper from Micron on the DDR4 memory is a great resource.
All in all, the capability of SDRAM to work with the CPU clock and the Double Data Rate makes it successful in its field. By utilizing both the rising and falling edges of a clock signal, the SDRAM achieves a higher bandwidth than standard DRAM. This is known as double data rate (DDR). For example, if the clock speed is 100 MHz, SDRAM can effectively perform operations at a rate of 200 MHz. The CPU clock also controls the process of pre-charging in SDRAM, playing a crucial role in reducing latency.
Purpose and Deployment of SDRAM
The RAM that we install in our computers as the main memory has a technical name, SDRAM. Before the release of SDRAM in 1996, computers used everyday Asynchronous DRAM. The SDRAM DIMM modules are used to work in conjunction with the CPU in real-time to store data and instructions. SDRAM enables quick access and processing because of its low latency and high bandwidth. Although it is slower than SRAM, which is used as a cache in the CPU, it serves perfectly as a buffer between the Cache and secondary storage, such as SSD or HDD. The data required by the CPU is picked from the primary storage and loaded into the SDRAM first. Then, the required data is loaded to the cache and then to the registers for processing. DRAM is volatile but offers high performance, making it ideal as a temporary memory in computers.
It is easy to get confused between DRAM and SDRAM because people often refer to RAM as DRAM, despite the technical name being SDRAM. In 2024, no modern computer will use everyday DRAM or Asynchronous DRAM, as SDRAM has taken over everywhere.
An Image of DDR3 SDRAM SO-DIMM Module in a Laptop:
A desktop DDR5 SDRAM module resembles this and has a larger form factor than the laptop RAM module.
Double Data Rate (DDR) in DRAM
| DDR Variant | Introduced | Data Rate (GB/s) | Typical Frequency (MHz) | Key Features |
|---|---|---|---|---|
| DDR1 | 1996 | Up to 2.1 | 100 – 200 | Basic double data rate; largely obsolete. |
| DDR2 | 2003 | 4.8 | 200 – 800 | Improved performance; lower power consumption than DDR1. |
| DDR3 | 2007 | 6.4 to 17 | 400 – 1600 | Further speed improvements; lower power (1.5V). |
| DDR4 | 2014 | 12.8 to 25.6 | 1600 – 3200 | Significant speed and capacity improvements; more efficient (1.2V). |
| DDR5 | 2020 | 32 and higher | 4800 – 8400 | Double the bandwidth and capacity of DDR4; improved efficiency (1.1V). |
| DDR6 | Expected 2024 | 40 and above | 6400 – 12000 | Enhanced bandwidth and capacity; further power efficiency improvements anticipated. |
With the improvement of DDR variants, the performance and data rate of SDRAM also improve. As we discussed earlier, the DDR utilizes both the rising and falling edges of the clock signal to double the data rate. However, the performance improvements aren’t just limited to the DDR. The maximum clock frequency enables the achievement of high data rates and performance.
In simple words, the RAM with a clock speed of 4800 MHz is working at just 2400 MHz. The DDR allows it to use the same clock speed for double data transmission. Also, because the CPU’s clock speed is generally much higher than the RAM speed, the memory controller coordinates the communication. CPUs can execute multiple operations or instructions within a single clock cycle. For example, at 4 GHz, a CPU can execute billions of cycles per second. This enables the CPU to issue multiple requests to RAM, leveraging its ability to manage high-speed operations efficiently.
Additionally, the external RAM, or DIMM module, has minimal direct interaction with the CPU cores, as it interacts with its own cache memory (L1, L2, L3). The memory controller on the CPU ensures that the required data is accessed from RAM efficiently, utilizing its highest clock frequency.
3. What is SRAM (Static Random Access Memory)?
Static Random Access Memory is another variation of RAM that is volatile but doesn’t need refreshing like DRAM. In SRAM, transistors are used in the form of flip-flops to form memory cells. A single memory cell has six transistors in the formation shown below. Although the transistors require constant power to function, there is no charge leakage; hence, a refreshing mechanism is necessary. This quality, combined with the rapid switching of the transistors, makes SRAM the fastest type of RAM in the entire computer system.
SRAM is called memory, but you can consider it an active circuitry that allows data to be stored and processed almost instantly. SRAM has the lowest storage density compared to other types of RAM. Also, it has very high power consumption. But it comes with the highest levels of reliability and performance.
Purpose and Deployment of SRAM
SRAM is primarily used in CPU caches (L1, L2, and L3) and registers. Additionally, it is utilized in buffers of GPUs, modems, network switches, and routers. Some printers may also use SRAM. However, the most significant application of SRAM is primarily in computer CPUs. The latency of SRAM can be as low as 1 to 3 nanoseconds. The L1 cache, utilizing SRAM, offers the best performance and lowest latency.
The main purpose of SRAM is to provide ultra-high-speed data access to critical components in different systems, including computer CPUs. SRAM is typically used in petite sizes, but only at places where it is necessary to consider the cost. In simple words, you will find SRAM only where speed and data consistency are critical.
4. What is VRAM (Video Random Access Memory)?
VRAM is technically a type of DRAM, but optimized for storing images and video data that the GPU (Graphics Processing Unit) requires for processing different graphics. It is primarily responsible for storing textures, frame buffers, image data, video data, and other graphics-related data. VRAM has the main optimization of higher bandwidth. A GPU generally accesses multiple memory parts simultaneously when working on graphics. In simple terms, VRAM can be accessed simultaneously by both the display system and the GPU, which is why it is referred to as dual-ported memory. In this way, the GPU can process the next frame while the existing one is being displayed.
Modern VRAM is of two types, i.e., GDDR (Graphics DDR) and HBM (High Bandwidth Memory). GDDR is a single-layered memory, while HBM is a stacked or multi-layer memory. GDDR VRAM is primarily used in consumer graphics cards, such as those from NVIDIA GeForce and AMD Radeon. HBM is utilized in high-end GPUs and data centers. Another application can be found in AI accelerators, such as NVIDIA Tesla and AMD Radeon Pro. HBM has its main application in various fields of high-performance computing.
The VRAM connects to the GPU through a wide bus (generally 128-bit, 256-bit, or 512-bit) to ensure a fast data exchange. The connection occurs via a dedicated bus, designed for parallel processing and handling large data sets. Inside a graphics card, you can see the VRAM connected to the GPU separately, allowing for higher bandwidth and lower latency.
Purpose and Deployment of VRAM
The primary purpose of VRAM is to store graphics-related data. GPUs excel at performing repetitive tasks that are less complex than those handled by the CPU. To perform its job effectively, it can utilize extremely high data transmission speeds. VRAM is used to fulfill those demands. You will find VRAM mostly in Graphics cards (both consumer and enterprise) and integrated GPUs in CPUs, such as game consoles, VR/AR devices, etc. The computers working on AI and Deep Learning also utilize a very high amount of VRAM with powerful GPUs.
Conclusion
To conclude, DRAM is an outdated type of RAM variant used in older systems as the primary memory. However, with the advent of SDRAM, DRAM became extinct. SDRAM is a variant of DRAM itself. The only significant issue with these RAMs is that they need constant refreshing because they use capacitors as the storage medium, which discharge slowly even if you try to isolate them with the help of a transistor. SRAM is an entirely different technology, utilizing the fast switching of transistors as temporary memory. Because there are no capacitors, there is no charge leakage, and hence, simpler circuitry.
Additionally, because transistors are used, data is stored and accessed almost instantly with very low latency, reaching nearly one nanosecond. The VRAM has its application in graphics-related tasks. VRAM is found where very high bandwidth and throughput are demanded. Some key optimizations in the VRAM dual-porting are high clock speeds, compression techniques, and tiling.
Thanks for reading!
