Dynamic Random Access Memory (DRAM) Explained

What is Dynamic Random Access Memory (DRAM)?

Dynamic Random Access Memory refers to the specific type of volatile semiconductor memory that stores the bits in the memory cells as 0s or 1s depending on the charging or discharging of the capacitor.

Technically, these memory cells consist of a small capacitor and a transistor that are built on Metal Oxide Semiconductor technology.


  • A DRAM is a low cost option to store data more efficiently in much less space than a Static RAM in the tiny capacitors. However, it needs to be refreshed continuously thereby using more power.
  • A DRAM is available in different Integrated Circuit packages such as Dual Inline package and Surface Mount package.
  • There are two specific formats in which a DRAM may be available namely the Single Inline Memory Modules and Dual Inline Memory Modules.
  • The types of DRAM are also varied and include SDRAM, RDRAM, FPM DRAM, EDO DRAM, BEDO DRAM, Asynchronous DRAM, Synchronous DRAM, Video DRAM, Windows DRAM, Multibank DRAM, SGRAM and GDDR SDRAM.
  • A DRAM chip is used as the main memory in digital electronics, graphics cards, video game consoles, storage in personal computers, battery controlled applications, in networking and more.

Understanding Dynamic Random Access Memory (DRAM)

Understanding Dynamic Random Access Memory (DRAM)

Dynamic Random Access Memory technically uses the capacitor in it to store each bit of data but for a very short time, often measured in milliseconds.

A DRAM is considered to be a more efficient means to store data because it needs little space to store them in comparison to a Static RAM or SRAM.

However, this capacitor that retains the data needs to be refreshed continuously and therefore a DRAM consumes more power.

Still, it is the low cost of manufacturing of the DRAM that makes it so favored and commonly used in computers today.

Also, with the use of a DRAM the cost per Megabyte is also reduced because a large number of capacitors can be packed on a single chip.

However, when it comes to speed of reading it seems to lag a bit with reference to the needs of the microprocessors of the latest generations.

The capacitor used in the design of the DRAM can be charged or discharged.

These two states of the capacitor indicate two separate values of bit that are traditionally called 1 and 0.

This semiconductor memory comes in the form of an IC or Integrated Circuit chip that is loaded with dozens to billions of memory cells.

DRAM Integrated Circuits Packages

You will get the DRAM chips in different Integrated Circuit or IC packages.

These are:

  • DIL or Dual-in-line package – This is a regular leaded package for IC and
  • SMT or Surface Mount package – This conforms to normal SMT packages and the basic format and size depend on the size of the silicon chip, the type of application it is designed for and the number of leads needed.

DRAM Module Formats

What is Dynamic Random Access Memory (DRAM)

The multi-chip modules are typically available in diverse types of formats. One of the formats was SIMM or Single Inline Memory Module which is usually not used now.

Typically, these modules have 30 pin and 72 pin sets and offer 32-bit data transfer rates.

The most commonly used format of DRAM is the DIMM or the Dual Inline Memory Module.

These modules get their name based on the arrangement of the pins in them which are typically located on both its sides.

The DIMMs originally came with a 168-pin connector.

These modules supported a 64-bit data bus, which is double than that of the SIMMs and more data passing through it.

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This results in faster performance of it, overall.

However, the most modern DIMMs are designed on the 4th generation Double Data Rate or DDR4 SDRAM.

These come with a 288-pin connector for which offers much higher and faster data output.

There are different DIMM categories of such DRAMs that are categorized according to their varied Integrated Circuit architectures.

These are:

  • Un-buffered DIMMs or UDIMMs that are usually used on desktop and laptop computers
  • Fully buffered DIMMs or FB-DIMMs that are used in larger memory systems for their reliability
  • Registered DIMMs or RDIMMs that are stable and used in the servers and
  • Load Reduced DIMMs or LR-DIMMs that use Isolation Memory Buffer or iMB for buffering data and address lanes both.

Types of Dynamic Random Access Memory

There are different types of DRAM available and all of them have different features and functionality.

Here is the list of all along with a brief description against each:

  • SDRAM – The full form of SDRAM is Synchronous Dynamic Random Access Memory. It is faster than a regular DRAM and works by synchronizing with the bus of the Central Processing Unit of the system based on the clock synchronization.
  • RDRAM – The full form of RDRAM is Rambus Dynamic Random Access Memory. This particular type of DRAM has a much higher operating speed in comparison to the other types of DRAMs.
  • FPM DRAM – The full form FPM DRAM is Fast Page Mode Dynamic Random Access Memory. These types are seldom used nowadays due to its lower speed of usually 66 MHz.
  • EDO DRAM – The full form of EDO DRAM is Extended Data Out Dynamic Random Access Memory. The design of this type of DRAM offers faster performance at a low cost in comparison to the FPM DRAM.
  • BEDO DRAM – The full form of BEDO DRAM is Burst EDO DRAM. This type of DRAM can process as many as four memory addresses in a single burst thereby saving three clock cycles.

In addition to the above, there are a few specific types of DRAMs that need specific mention and explanations such as:

Asynchronous DRAM – This type of DRAM does not work as per the synchronization of the clock.

There is a memory controller which is instead synchronized with the clock that results in a slow speed. These types of DRAMs can be further categorized as follows:

  • RAS only Refresh or ROR asynchronous DRAM – These types of DRAMs are classic. It gets refreshed by opening every row in turn.
  • CAS before RAS refresh or CBR asynchronous DRAM – This type of DRAM reduces external circuitry.

Synchronous DRAM – In this type of DRAM the memory interface and the clock is synchronized and all signals are processed on its rising edge.

These types of DRAMs are also further categorized as follows:

  • SDR SDRAM or Single Data Rate SDRAM that makes a single data transfer per clock cycle
  • DDR SDRAM or Double Data Rate SDRAM that includes DDR2, DDR3, and DDR4 SDRAMs and use double pinning to double the bandwidth and transfer data on rising and falling edges both of a clock signal and
  • RLDRAM or Reduced Latency DRAM that offers faster and higher performance with more bandwidth.

Then there are the different types of graphics asynchronous and synchronous DRAMs that help in graphics based jobs such as texture memory and frame buffers on video cards.

A few of these DRAMs are:

  • Video DRAM or VRAM which is dual ported and used to store the frame buffer in graphics adaptors
  • Window DRAM or WRAM that costs less and performs better than VRAM with up 25% greater bandwidth offered
  • Multibank DRAM or MDRAM that comes with little memory banks of 256 KB and operates in interleaved fashion so that two banks work in one clock cycle
  • Synchronous Graphics RAM or SGRAM which is single ported and comes with additional functionalities such as block write and bit masking and can also open two memory pages simultaneously and
  • Graphics Double Data Rate SDRAM or GDDR SDRAM that is typically used in the main memory of GPUs or Graphics Processing Units.
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The GDDR SDRAM, however, is quite different from DDR SDRAM even if they both share a few core technologies.

The main characteristics of it are better clock frequencies of I/O interface and DRAM core which offers much higher memory bandwidth for the GPUs.

How Does Dynamic Random Access Memory Work?

The working of the DRAM usually depends on its design which comprises a rectangular arrangement of storage cells with a single capacitor and transistor for every data bit.

There are also long horizontal lines that connect every row called the word lines. There are two bit lines in every column of cells.

Each of these lines are connected to the other storage cell in the column and are usually referred to as ‘+’ and ‘−‘ bit lines.

There is a sense amplifier which is actually a pair of inverters that are cross-connected between the bit-lines.

One of these inverters is linked with the input received from the + bit-line and the output sent to the − bit-line and the other is connected in the opposite way, i.e. it gets the input from the − bit-line and sends output to the + bit-line.

This produces a positive feedback which, in turn, steadies after a bit-line is at its highest voltage and the other at its lowest.

The process of reading and writing data involves the following steps:

  • The sense amplifiers are disengaged
  • The bit-lines are pre-charged between high and low logic level voltages
  • The pre-charge circuit is turned off
  • The word-line of the desired row is driven high to connect to the bit-line of a storage capacitor of a cell to conduct and transfer charge
  • The sense amplifiers are re-connected to the bit-lines pairs
  • The output of the sense amplifier is latched by sensing storage cells in the open row at the same time and
  • The current flows back from the sense amplifier output up the bit-lines during this period in order to recharge the storage cells.

When reading is completed all the columns in the open row and word-line are switched off in order to disconnect the storage cell capacitors.

While writing to the memory or storing data, the sense amplifier of a specific column is forced temporarily to the required high and low voltage status when a row is opened.

This helps the capacitor of the cell storage to be charged or discharged to reach the required value by the bit-line.

The positive feedback pattern of the sense amplifier holds a bit-line at a steady voltage even if the temporarily forced voltage is taken away.

While writing to a specific storage cell of the DRAM every column in a row is sensed as it is done while reading the memory.

This means that the complete row is written back in or refreshed even though the charge of only one column of the storage cell capacitor is changed.

Uses and Importance of Dynamic Random Access Memory

A DRAM chip in a computer plays an important role and is extensively used today in digital electronics that need high capacity but low cost memory.

It is used as the main memory in the computer systems and the graphics cards as well.

In addition to that, it is also used in several other portable machines and video game consoles.

As for the other uses of the Dynamic Random Access Memory, the list is pretty long and includes:

  • As a cost-efficient storage in personal computers
  • In networking
  • In battery controlled synchronous and asynchronous applications and
  • For enhancing the graphics functions of the computer.

Dynamic RAM is very important for a computer which is why it has been so extensively used in personal and home computers for about 20 years now.

One of the most significant reasons for its importance is that the DRAM is optimized for low leakage.

However, the speed of it is a bit of a concern which is however compensated by the low cost of the Dynamic RAM. As compared to the Static RAM, it is about one-eighth.

Therefore, Dynamic RAM is extensively used in those areas where a large amount of data needs to be stored and a cost efficient solution is required for that.

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This includes a variety of processor based equipment which is one of the cornerstones of the DRAM memory technology.

It is the denser memory and a reasonably fast performance of the DRAM that makes it so useful today, and with it developing continuously, it will surely meet the ever increasing demands of the new equipment.

Most importantly, the Dynamic RAM is located very close to the CPU which ensures much quicker and easier access to the necessary programming codes and data by the processor for processing.

It allows the CPU to directly access any segment of the memory instead of proceeding in a specific sequence from the initial point.

It is the DRAM that allows the computer to use and rewrite the code and data and even store them temporarily in real time. This adds to its importance.

Is Dynamic Random Access Memory Just RAM?

Ideally, Dynamic RAM is a common type of RAM for sure and there are many different types under this category, which is already mentioned before.

Like RAM, Dynamic RAM stores data and information needed by the processor and is also highly volatile.

However, it is not just RAM because it helps different components of the computer in performing well due to the wide variance of it.

It is quite fast and comes in different latency and speed options.

You will typically get the best results if you look for a Dynamic RAM that comes with a higher speed, usually measured in MHz, and a lower latency number, indicated as CL.

Where is Dynamic Random Access Memory Used in a Computer?

As said earlier a Dynamic RAM is usually used in personal computers as well as in workstations and servers.

And, depending on its types, it is also used in different other hardware peripherals of a computer as well such as in the graphics cards.

What are the Advantages of Dynamic Random Access Memory?

The benefits offered by a Dynamic Random Access Memory are varied and include:

  • A straightforward design
  • High reliability
  • Low-cost storage option
  • Lower space requirement
  • Lower heat dissipation
  • Higher integration density
  • Simpler memory but denser cell structure.

On the other hand, there are also a few downsides of using DRAM that are also good to know. These are:

  • Inter-signal coupling in multiple DRAMs
  • Higher power consumption
  • Extreme volatility
  • Needs continuous refreshing
  • Relatively lower operational speed
  • A complex manufacturing process.

Still, in spite of these downsides, the benefits offered by Dynamic RAM makes it so useful and favored among the users today.

What is Dynamic Random Access Memory Frequency?

Dynamic RAM frequency indicates the amount of data transferred in a second through a particular data line. This is typically expressed as a percentage.

Ideally, the frequency of the Dynamic RAM is actually half of the speed in comparison to the speed of RAM but it is the DDR or Double Data Rate aspect that doubles it.

Typically, DRAM frequency is expressed in MHz. Ideally different generations of DDRs will offer different frequency of Dynamic RAM, which can be tabulated as follows:

  • DDR 1, 200 to 400 MHz
  • DDR 2, 400 to 1000 MHz
  • DDR 3, 800 to 1600 MHz
  • DDR 4, 2400 to 4400 MHz and
  • DDR 5, 4800 to 8400 MHz.

Typically, Dynamic RAM frequency is very useful for jobs like 3D artwork, rendering, video editing, or gaming.

Higher the frequency, the better will be the performance.

What is Dynamic Random Access Memory Made up of?

Usually, the Dynamic RAM consists of memory cells each of which is made up of a capacitor and a MOSFET or Metal Oxide Semiconductor Field Effect Transistor inside an Integrated Circuit.

As said earlier, it is the capacitor where the data is stored.


So, that is what you need to know about the Dynamic Random Access Memory used in the computer as an average user.

Though there are lots of other technical aspects involved in it, this knowledge is quite comprehensive to start and win a debate on which among Dynamic and Static RAM is important.

About Puja Chatterjee

Puja ChatterjeePuja Chatterjee is a technical writer with extensive knowledge about computers. She graduated from BIMS. Her expertise includes technology writing and client relationship management gained through over 12 years of experience. Follow Her at Linkedin.

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