Types of RAM | DRAM | SRAM | SDRAM | SDR SDRAM | DDR SDRAM | GDDR SDRAM- thebytewise

Nearly every device which has any kind of computational capabilities needs a RAM. Everything starting from smartwatches to Android TVs to super-computer all has some kind of RAM technology used in it. Although all RAM basically serves the same purpose, there are a few types of them commonly in use today. But before going to that, lets first discuss what actually RAM(a.k.a Internal memory) is and how is it different from the external memory.



What is internal memory and external memory?


Internal memory, also known as "main memory or primary memory", generally the main memory stores a small amount of data that is accessed quickly while the computer is running. RAM(Random Access Memory) is used for storing temporary data that means it is a type of volatile memory, it stores common data that programs are constantly using.


External memory, also known as "Secondary memory", refers to all the external storage devices like SSD, HDD, USB flash drives, optical drives, etc. These are Non-Volatile memory, which means, unlike RAM external memory devices can retain data even after the computer is turned off or the power supply is cut. SSDs use NAND flash module to store data which can retain its charge even when it's not being powered. Although it is a storage device, RAM is several degrees faster than a typical SSD or HDD.


But not to confuse External memory with ROM(Read Only Memory), it is also a type of Non-Volatile memory but its main purpose is to store system firmware. Unlike HDD/SSD data stored in ROM can only be modified very slowly or Not at all. The BIOS is special software that interfaces the major hardware components of your computer with the Operating System. It is usually stored on a Flash memory chip on the Motherboard, but sometimes the chip is just another type of ROM.


Types of RAM


Static RAM (SRAM): The SRAM was invented at Fairchild Semiconductor in 1964 by an electrical engineer named John Schmidt. One of the two basic types of memory(the other one being DRAM), SRAM requires a constant flow of power to retain data, unlike DRAM, SRAM doesn't need to be refreshed periodically, this is the reason it is called 'static', i.e no change or action is needed to keep data intact, SRAM is a volatile memory that means all the data stored in it will be lost once the power supply is cut.

SRAM is generally used in devices like Digital cameras, routers, printer, LCD screens, etc.

The advantage of using SRAM is that it consumes less power and also the data access speeds are faster than DRAM. But there are some disadvantages also, SRAM has lesser memory capacities and also the cost of manufacturing is high.

Because of these characteristics SRAM is still used in CPU cache, Hard drive buffer/cache, or other memory which requires running at high speeds.


Dynamic RAM (DRAM): DRAM was invented in 1967 by Robert Heath Dennard, unlike SRAM, DRAM requires a periodic refresh of power in order to function properly. The capacitors that store data in DRAM gradually discharge energy over time, no energy means the data will be lost. This is why DRAM is called 'dynamic', i.e constant change or action is needed to keep data intact. DRAM is also a volatile memory that means the data will be lost when the power is cut.

DRAM is asynchronous, which means it responds immediately to any data input, without waiting for the CPU clock signal.

The advantage of using DRAM is that the manufacturing cost is lower than SRAM and also the memory capacity is also larger than SRAM. But the disadvantages of being low data access speed and higher power consumption.

Because of these characteristics DRAM is generally used as system memory and video graphic memory.


Synchronous Dynamic RAM (SDRAM): It is a classification of DRAM that operates in sync with the CPU clock, which means it waits for the CPU clock signal before responding to data inputs.

The benefit of synchronous operation is that a CPU can process overlapping instructions parallelly, also known as pipelining, which is the ability to receive new instruction before the previous instructions have been completely resolved.

Although pipelining doesn’t affect the time it takes to process instructions, it does allow more instructions to be completed simultaneously. Processing one read and one write instruction per clock cycle results in higher overall CPU performance. SDRAM supports pipelining because its memory is divided into separate banks.

The SDRAM is also known as Single Data Rate Synchronous Dynamic RAM (SDR SDRAM), the 'Single Data Rate' indicates how the memory processes one read and one write instruction per clock cycle.

The SDR SDRAM works at 3.3V.


Double Data Rate Synchronous Dynamic RAM (DDR SDRAM): It is the second-generation development of SDR SDRAM. DDR SDRAM works just as an SDR SDRAM but only at twice as fast rates. That means DDR SDRAM is capable of two reads and two write instructions per clock cycle of the CPU.

Although the same functionality, DDR SDRAM has some physical differences like 184 pins and a single notch on the connector versus 168 pins and two notches on the connector of SDR SDRAM. DDR SDRAM also works on lower voltages(2.5V) and the clock speed tops at 200 MHz.


  • DDR2 SDRAM is the upgraded version of a DDR SDRAM. It is just a faster version of DDR SDRAM while keeping the same 'Double Data Rate', it is faster because it can run on higher clock speeds that top out at 533 MHz. DDR2 SDRAM also runs at a lower voltage of 1.8V and uses a 240 pin configuration.

  • DDR3 SDRAM is the upgraded version of DDR2 SDRAM, it has greater reliability, greater memory capacity, and also lower power consumption (1.5V), and its clock speed also reaches to 800MHz. DDR3 SDRAM also uses a 240 pin-configuration.

  • DDR4 SDRAM is again an improved version of DDR3 SDRAM with more advanced reliability, even greater memory capacity, and even lower power consumptions(1.2V) with of course higher clock speeds of up to 1600MHz. DDR4 SDRAM uses a 288-pin configuration.

Graphics Double Data Rate Synchronous Dynamic RAM (GDDR SDRAM): As the name suggests it is a type of DDR SDRAM that is specifically designed for video graphics rendering, in conjunction with a dedicated GPU(Graphics Processing Unit) on a video card.

Similar to DDR SDRAM, GDDR SDRAM also has its own evolutionary line with increased performance with lower power consumption(GDDR2 SDRAM, GDDR3 SDRAM, GDDR4 SDRAM GDDR5 SDRAM).

Although they share very similar characteristics, GDDR SDRAM and DDR SDRAM is not exactly the same. GDDR SDRAM is expected to process a massive amount of data, and also to have low latency to immediately respond to the CPU.

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