In the previous article, we discuss the types of RAM in computers, and in this article, we will see the different types of DRAM (Dynamic Random Access Memory) and DDR SDRAM (Double Data Rate Synchronous DRAM). So Let’s dive into the topic!
Now, if you see this Random Access Memory or RAM, it is an essential part of any computing device. So, whether you see the laptop, or mobile, or any gaming console you will find this RAM on all these devices.
We have already seen some of the articles regarding these Random Access Memories, and in fact, in the last article, we have compared the static RAM and the dynamic RAM in many aspects.
So, now in this article, let us see the different types of dynamic RAM, and let’s compare the different generations of dynamic RAM in different aspects.
So, we will compare the different types of dynamic RAM in terms of their speed or bandwidth, in terms of their packaging standards in which they are available.
And we will also see the different types of dynamic RAM in terms of the applications to which they are used.
Types of DRAM (DRAM Generations):
So, now if you see the different generations of DRAM (Dynamic RAM), in each generation you will find that an improvement in the speed as well as the reduction in the power consumption.
1. Asynchronous DRAM:
So, if you see the very old generation of dynamic RAM, they were the Asynchronous Dynamic RAM. It means that the RAM is not synchronized with the CPU clock.
The disadvantage of this type of RAM is that the CPU does not know the exact timing at which the data will be available from the RAM on this input-output bus. And that problem has been overcome by the next generation of RAM, which is known as the Synchronous DRAM (SDRAM).
2. Synchronous DRAM (SDRAM):
In the case of this SDRAM, the RAM is synchronized with the CPU clock. Now, the advantage of this SDRAM is that the CPU or to be precise memory controller exactly knows the timing or the number of cycles after which the data will be available on the bus.
So, the CPU does not need to wait for memory access. And because of that we can increase the memory read and write speed.
Before we understand this SDRAM, let’s see the different terminologies which are quite often used with this dynamic RAM. If you see this RAM, we have a total of two types of different frequencies. They are given below.
- Input-output Clock Frequency
- RAM Internal Clock Frequency
This input-output clock frequency is the frequency at which the data is being transferred between the RAM and the memory controller. And the internal clock frequency of the RAM is the frequency that is being used by the RAM for the internal operations.
Here in the case of this Synchronous DRAM this input-output clock frequency and the internal clock frequency of the RAM is the same. For suppose if the internal clock frequency of the RAM is 100 MHz then the input-output clock frequency is also 100 MHz.
And generally, in this synchronous DRAM, the operating frequency is in the range of 100 to 133 MHz. If you find the PC-100 on the SDRAM module, it means that the input-output bus clock frequency is 100 MHz.
And data that is being transferred between this RAM and the memory controller is at the rate of 100 megabits transfer per second.
And if this bus is 64 bit wide, then the data rate in terms of the bits per second will be equal to 100 MHz into 64 bits. If we convert it into the bytes (per second) then it will be divided by the 8 bits. i.e., 800 Megabytes per second. These synchronous DRAM modules are operated at 3.3V.
Types of SDRAM (or) SDRAM Generations:
Single Data Rate SDRAM Vs Double Data Rate SDRAM (DDR RAM)
“This SDRAM or Synchronous DRAM is also known as the Single Data Rate SDRAM”.
Because in this RAM, the data is transferred at every rising edge of the clock cycle. But if you see the next generation of synchronous DRAM they are known as the DDR RAM (Double Data Rate SDRAM).
Because in the case of this DDR RAM, the data is transferred twice during the clock cycle. That is during the positive edge as well as during the negative edge. So, in this way, the data is being transferred twice during each cycle. “That is why it is known as the Double Data Rate SDRAM or DDR SDRAM or DDR RAM”.
Let’s see the different generations of this DDR RAM.
Types of DDR SDRAM (or) DDR RAM Generations:
If you see this DDR RAM, there are different generations of DDR RAM. Starting from the DDR1 up to the DDR5. Nowadays, the memory that we use inside the desktop, laptop, or mobile is either DDR3 or DDR4 RAM.
So, let’s see the different generations of the DDR SDRAM or DDR RAM one by one.
DDR RAM 1st Generation (DDR1 RAM):
The first generation of DDR RAM is known as the DDR1 RAM. Compared to the SDRAM here, the voltage has been reduced from 3.3V to 2.5V.
As I said earlier in the case of DDR RAM, the data is being transferred both during the rising as well as the falling edge. So, we can say that in the single clock cycle, instead of 1 bit, 2 bits are being pre-fetched. That is generally known as the 2-bit prefetch.
Here in the case of DDR1 RAM, the internal clock frequency, as well as the input-output bus clock frequency, are the same.
Generally, this DDR1 RAM is operated in the range of 133 MHz up to 200 MHz. But if you see the data rate at the input-output bus, it will be double compared to the clock frequency.
As, in the case of this DDR RAM, the data is transferred both during rising as well as the falling edge. Suppose if you are operating this DDR1 RAM at 133 MHz then you will see the data rate as 266 Mega transfer per second.
For suppose if the bus frequency is 200 MHz then the data transfer rate will be equal to 400 Mega transfer per second. And the input-output bus is 64 bits wide, then the data rate in terms of the bytes per second will be equal to 3200 Megabytes per second.
These DDR RAMs are generally denoted by the term DDR followed by the transfer rate of this RAM. And if you see the DDR1 module or DDR1 stick, then on that stick you will find the term which is used as PC-3200.
It means that the maximum speed or the maximum bandwidth which can be achieved by this DDR1 RAM is 3200 Megabytes per second.
DDR RAM 2nd Generation (DDR2 RAM):
After the first generation of DDR1 RAM, the second generation of DDR RAM is DDR2 RAM. So now in the case of this DDR2 RAM, it is operated at 1.8 V instead of 2.5 V.
And if you see the internal RAM clock frequency, the internal RAM clock frequency is the same as the previous generation. But here the data rate is doubled compared to the last generation.
And that is being achieved by increasing the number of bits that are being pre-fetched during each cycle. So, in the case of this DDR2 RAM instead of 2 bits, here 4 bits are pre-fetched during each cycle (or) in a simple way if I say, in the case of this DDR2 RAM, the internal bus width of this RAM has been doubled.
For suppose if the input-output bus is 64 bits wide, then the internal bus width of this RAM will be equal to 128 bits. So, in this way, in a single cycle, we can handle double the amount of data.
And to handle the same amount of data, the clock frequency of this input-output bus should be doubled. So this DDR2 RAM is operated at 100 MHz internal clock frequency then the input-output bus should have the clock frequency of 200 MHz.
And in the case of this DDR RAM, as data is transferred both during rising and falling edge, so the data rate will be doubled compared to the clock frequency, which is 400 mega transfer per second.
And in terms of the DDR terminology, it can be written as DDR followed by the transfer rate. If DDR2 RAM is operated at 400 MHz clock frequency, then the data rate will be equal to 800 mega transfer per second. And in terms of the terminology, it can be written as DDR2-800.
And if you see the DDR2 module, on the module it will be written as PC2-6400. This means the data rate in terms of the bytes per second.
DDR RAM 3rd Generation (DDR3 RAM):
After the second generation, the third generation of DDR RAM is the DDR3. In the case of this DDR3 RAM, the voltage is further reduced from 1.8V to 1.5V.
The internal clock frequency of the RAM, it is slightly improved compared to the last generation. But the data rate that you can achieve with the same frequency has been doubled compared to the previous generation.
Because in the case of this DDR3 RAM, here the number of bits that is being pre-fetched has been increased from 4 bits to 8 bits (or) in a simple way, if I can say, the internal data bus width of RAM has been increased 2 times compared to the last generation.
So, in the case of this DDR3 RAM, suppose if the internal clock frequency is 100 MHz, then to match the data rate, the input-output bus should be operated at 4 times the clock frequency that is 400 MHz. And the transfer rate that you get will be equal to 800 mega transfers per second.
So, now on any DDR3 module, if you find the term DDR3-800 followed by PC3-6400, it means that this RAM is DDR3 RAM which is operated at 1.5 V and the clock frequency of this RAM is 400 MHz.
And the maximum transfer rate which can be achieved is 800 mega transfer per second. And the maximum bandwidth of this RAM is 6400 Megabytes per second.
DDR RAM 4th Generation (DDR4 RAM):
After the third generation of DDR3 RAM, the next generation is DDR4 RAM.
Now, in the case of this DDR4 RAM, again the operating voltage has been reduced from 1.5 V to 1.2 V. And here again, in the case of this DDR4 RAM, The number of bits that are being pre-fetched is the same as the previous generation i.e., 8 bits per cycle.
But now in the case of this DDR4 RAM, the internal clock frequency of the RAM has been increased. If you are operating at 400 MHz then the clock frequency of the input-output bus should be 4 times, which means 1600 MHz.
And the transfer rate will be equal to 3200 Mega transfers per second. So, on the module, you will find the term that is PC4 followed by 25600. That is the speed in terms of Megabytes per second. And in terms of the DDR terminology, you will find it as DDR4 followed by the 3200.
So far whatever discussion that we carried out we have assumed that the input-output, the bus width is 64 bits. But if we increase this bus width, let’s say if we double the bus width then the theoretical data rate that can be achieved will be getting doubled.
So, whenever this RAM is used in such a mode, then it is known as the dual-channel mode. For suppose if you have two options, let’s say one 8 GB of DDR4 RAM which is used as a single-channel mode.
And two 4 GB of DDR4 RAMs are used as dual-channel mode, then the bandwidth which can be achieved with this two 4 GB of DDR4 RAM will be better compared to the single-channel 8GB of DDR4 RAM.
So far we have seen the different generations of these dynamic RAMs in terms of their speed and operating voltages. Now, let’s also see the different packages in which these dynamic RAMs are available.
Different types of Packages in DRAM:
There are two major package types in DRAM, they are given below.
- Single Inline Package
- Dual Inline Package
A very older generation of dynamic RAM was available in the Dual Inline Package. Then after the next generation of RAMs was available in the single In-Line Modules.
In the case of this Single In-Line module, memory chips are soldered onto the one PCB, and the pins are available on the single side of the PCB. That’s the reason, this package is known as the Single In-Line module, as the pins are available on only one side of the PCB.
Here this single In-line module can provide a data bus width of 32 bits. Suppose if you want 64 bits of the data bus, then you need to connect the two single In-line modules in parallel.
But then after the next generation of RAMs were available in the Dual In-Line Module (or) simply it is known as the DIMM.
So, in this Dual In-Line Module, it is possible to have 64 bits wide data bus. And in this case, the pins were available both in front as well as the back of the PCB. And that’s a reason, it is known as the Dual In-Line Module.
If you see the different generations of DDR RAMs, they were available in the DIMM modules. But all the modules have a different number of pins as well as different operating voltage.
So, in a way, all the four generations of RAMs are not either forward or backward compatible. If you are having a motherboard which is supporting DDR3 RAM, then it will not support either DDR2 or DDR4 RAM.
So, the DIMM modules which are available in this form factors are used inside the desktop or personal computer. But if you see inside the laptop the form factor of this DIMM module is quite compact. And it is known as the SO-DIMM or simply small outline DIMM Modules.
So, if you see the different generations of SO-DIMMs, it is having a different number of pins as well as different operating voltages.
So far whatever discussion that we carried out, we had assumed that this RAM is used on either a personal computer or laptop. But this RAM is also categorized based on the applications in which it is being used.
Let’s discuss some other applications of RAM. Some of them are LPDDR RAM & GDDR RAM.
What is LPDDR RAM?
“The dynamic RAMs which are used inside the Mobiles or Smartphones are known as the Mobile DDR RAM or Low Power DDR RAM (LPDDR) RAM”
So, these Low Power DDR RAMs are also having different generations. They are starting from LPDDR1 up to LPDDR5. If you see the 2021 flagships they are operated on this LPDDR5x RAM.
So, these LPDDR RAMs are optimized for low power consumption. Because these RAMs are used inside the smartphone which is having a small amount of battery. So, this type of RAM has to be optimized based on power consumption.
So, the operating voltage of this LPDDR RAM is less compared to the DDR RAMs which are used inside the desktop and the laptops.
What is GDDR RAM?
Similarly, the RAMs which are used for the Graphics cards are known as the Graphics DDR or simply GDDR.
Now, as this Graphical DDR is used for multimedia applications, So the amount of data that needs to be handled is quite more. That’s a reason, this type of GDDR RAM is more bandwidth compared to desktop and laptop memories.
That is all about the different types of RAM which are used in different applications.
So, I hope you got an overview of the different types of DRAM, SDRAM types, and DDR SDRAM types. Know more about the RAM on the Wikipedia official page.
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