The different sorts of dynamic RAM
We will see the various sorts of dynamic RAM. Now, if you see this random access memoryor RAM, it's the essential a part of any computer . So, whether you see the laptop, or mobileor any gaming console you'll find this RAM on of these devices.
let us see the various sorts of dynamic RAM and let's compare the various generations of dynamic RAM in several aspects. So, we'll compare the various sorts of dynamic RAM in terms of their speed or bandwidth, in terms of their packaging standards in whichthey are available. and that we also will see the various sorts of dynamic RAM in terms of the applications during which they're used.
So, now if you see the various generations of dynamic RAM, in each generation you'll find that the development within the speed also because the reduction within the power consumption.
Generation
So, if you see the very old generation of dynamic RAM, they were the asynchronous dynamic RAM. So, it means the RAM isn't synchronized with the CPU clock.
Disadvantage
Now, the disadvantage of this sort of RAMwas that CPU doesn't know the precise timing at which the info are going to be available from the RAM on this input-output bus. which problem has been overcome by subsequent generation of RAM, which is understood because the synchronous DRAM.
So, just in case of this SDRAM, the RAM is synchronized with the CPU clock.
Advantage
the advantage of this SDRAM is that the CPU or to be precise memory controller exactly knows the timing or the amount of cycles after which the info are going to be available on the bus. So, CPU doesn't got to await the access . and since of that we will increase the memory read and write speed.
So, now we before we understand about this RAM, let's examine the various terminologies which are very often used with this dynamic RAM.
So, if you see this RAM, we've total two sorts of different frequencies.
The first is that the input-output clock frequency and therefore the second is that the RAM internal clock frequency.
So, this input-output clock frequency is thefrequency at which the info is being transferred between the RAM and therefore the memory controller. and therefore the internal clock frequency of the RAM is that the frequency which is getting used by the RAM for the interior operations.
So, now here just in case of this synchronous DRAM this input-output clock frequency and therefore the internal clock frequency of the RAM are same. So, suppose if the interior clock frequency of the RAM is 100 MHz then the input-output clock frequency is additionally 100 MHz. and usually , if this synchronous DRAM the operating frequency is within the range of 100 to 133 MHz.
So, suppose if you discover the PC-100 on theSDRAM module, it means the input-output bus clock frequency is 100 MHz. And data that's being transferred betweenthis RAM and therefore the memory controller is at the speed of 100 mega transfer per second. And if this bus is 64 bit wide, then the datarate in terms of the bits per second are going to be adequate to 100 MHz into 64 bits. And if we convert it into the bytes(per second)then it'll be divided by the 8 bits. that's 800 Megabytes per second.
Now the synchronous DRAM modules are operatedat 3.3V. Now, this SDRAM or synchronous DRAM is alsoknown because the single rate SDRAM. Because during this RAM, the info is transferredat the every rising fringe of the clock cycle. But if you see subsequent generation of synchronousDRAM they're referred to as the DDR RAM. Because just in case of this DDR RAM, the datais transferred twice during the clock cycle. that's during the positive edge also asduring the negative edge. So, during this way, the info is being transferred twice during each cycle. which is why it's referred to as the doubledata rate or DDR SDRAM. So, if you see this DDR RAM, there are differentgenerations during this DDR RAM.
Starting from the DDR1 up to the DDR4. And now a days, the memory that we use insidethe desktop, laptop or mobile that's either DDR3 or DDR4 RAM. So, let's examine the various generation ofthis DDR RAM one by one.
The first generation of DDR RAM is knownas the DDR1 RAM.
So, compared to the SDRAM here, the voltagehas been reduced from 3.3V to the two .5V. So, like I said earlier just in case of DDR RAM,the data is being transferred both during the rising also because the falling edge. So, we will say that within the single clock cycle,instead of 1 bit, 2 bits are being pre-fetched. So, that's generally referred to as the two bit pre-fetch. Now, here in DDR1 RAM, the interior clockfrequency, also because the input-output bus clock frequency, are same. So, generally, this DDR1 RAM is operated within the range of 133 MHz up to the 200 MHz. But if you see the info rate at the input-output bus, it'll be double compared to the clock frequency. As, just in case of this DDR RAM, the info is transferredboth during rising also because the falling edge. So, suppose if you're operating this DDR1RAM at 133 MHz then you'll see the info rate as 266 Mega transfer per second. So, suppose if the bus frequency is 200 MHz then the info transfer rate are going to be adequate to 400 Mega transfer per second. And if the input-output bus is 64 bits wide,then the info rate in terms of the bytes per second are going to be adequate to 3200 Megabytes persecond.
Now, these DDR RAMs are generally denotedby the term DDR followed by the transfer rate of this RAM. And if you see the DDR1 module or DDR1 stick,then thereon stick you'll find that the term which is employed as PC-3200. It means the utmost speed or the maximumbandwidth which may be achieved by this DDR1 RAM is 3200 Megabytes per second. So, after the primary generation of DDR1 RAM.
The second generation of DDR RAM is DDR2 RAM.
So, now just in case of this DDR2 RAM, it's operatedat 1.8 V rather than 2.5 V. And if you see the interior RAM clock frequency,the internal RAM clock frequency is same because the previous generation. But here the info rate is double compared to the last generation. which is being achieved by increasing the amount of bits that's being pre-fetched during each cycle. So, just in case of this DDR2 RAM rather than 2bits, here 4 bits are pre-fetched during each cycle. Or during a simple way if I say, just in case of thisDDR2 RAM, the interior bus width of this RAM has been doubled.
So, suppose if the input-output bus is 64bits wide, then the interior bus width of this RAM are going to be adequate to 128 bits. So, during this way, during a single cycle, we canhandle double amount of knowledge . And to handle an equivalent amount of knowledge , theclock frequency of this input-output bus should be get doubled. So, suppose this DDR2 RAM, is operated at 100 MHz internal clock frequency then the input-output bus should have the clock frequencyof 200 MHz. And just in case of this DDR RAM, as data is transferredboth during rising and falling edge, therefore the rate are going to be doubled compared to theclock frequency, that's 400 mega transfer per second. And in terms of the DDR terminology, it canbe written as DDR followed by the transfer rate. So, now suppose if DDR2 RAM is operated at400 MHz clock frequency, then the info rate are going to be adequate to 800 mega transfer per second. And in terms of the terminology, it can bewritten as DDR2-800. And if you see the DDR2 module, on the moduleit are going to be written as PC2-6400. which suggests the info rate in terms of thebytes per second. So, after the second generation.
The third generation of DDR RAM is that the DDR3.
So, just in case of this DDR3 RAM, the voltageis further reduced from 1.8V to the 1.5V. Now, if you see the interior clock frequencyof the RAM, it's slightly improved compared to the last generation. But the info rate that you simply are able to do withthe same frequency has been doubled compared to the previous generation. Because just in case of this DDR3 RAM, here thenumber of bits that's being pre-fetched has been increased from 4 bits to the 8 bits. Or during a simple way, if I can say, the internaldata bus width of RAM has been increased 2 times compared to the last generation. So, just in case of this DDR3 RAM, suppose if theinternal clock frequency is 100 MHz, then to match the info rate, the input-output busshould be get operated at the 4 times the clock frequency that's 400 MHz. and therefore the transfer rate that you simply get will beequal to 800 mega transfer per second. So, now on any DDR3 module, if you discover theterm DDR3-800 followed by PC3-6400, it means this RAM is DDR3 RAM which is operatedat 1.5 V and therefore the clock frequency of this RAM is 400 MHz. and therefore the maximum transfer rate which may beachieved is 800 mega transfer per second and therefore the maximum bandwidth of this RAM is 6400Megabytes per second.
The next generation is DDR4 RAM.
Now, here just in case of this DDR4 RAM, againthe operating voltage has been reduced from 1.5 V to the 1.2 V.And here again, just in case of this DDR4 RAM, the amount of bits that's being pre-fetchedis same because the previous generation. that's 8 bits per cycle. But now just in case of this DDR4 RAM, the interior clock frequency of the RAM has been increased.
So, if you're operating at 400 MHz then theclock frequency of the input-output bus should be 4 times, meaning 1600 MHz. and therefore the transfer rate are going to be adequate to 3200Mega transfer per second. So, if you see the module, on the module youwill find the term that's PC4 followed by 25600. that's the speed in terms of Megabytes persecond. And in terms of the DDR terminology, you willfind it as DDr4 followed by the 3200. So, now thus far whatever discussion that wecarried out we've assumed that the input-output bus width is 64 bits.
But if we increase this bus width, let's sayif we double the bus width then the theoretical rate which will be achieved are going to be gettingdoubled. So, whenever this RAM is employed in such mode,then it's referred to as the twin channel mode. So, now suppose if you've got two options, let'ssay one 8 GB of DDR4 RAM which is employed as single channel mode. And two 4 GB of DDR4 RAMs which are used asdual channel mode, then the bandwidth which may be achieved with this two 4 GB of DDR4RAM are going to be better compared to the only channel 8GB of DDR4 RAM. So, now thus far we've seen the differentgenerations of this dynamic RAMs in terms of their speed and therefore the operating voltages.
Now, let's also see the various packagesin which these dynamic RAMs are available. So, very older generation of dynamic RAM wasavailable within the Dual Inline Package. Then after subsequent generation of RAMs wereavailable within the single In-Line Modules. So, just in case of this Single In-Line module,memory chips are soldered onto the one PCB, and therefore the pins are available on the only sideof the PCB. So, that's the rationale , this package is knownas the only In-Line module, because the pins are available on the sole one side of thePCB.
Now, here this single In-line module can providedata bus width of 32 bits. So, suppose if you would like 64 bits of the databus, then you would like to attach the 2 single In-line modules within the parallel. on the other hand after subsequent generation of RAMswere available within the Dual In-Line Module. or just it's referred to as the DIMM. So, during this Dual In-Line Module, it's possibleto have 64 bits wide data bus. And during this case, the pins were availableboth ahead also because the back of the PCB. which may be a reason, it's referred to as the DualIn-Line Module.
Now, if you see the various generation of DDR RAMs, they were available within the DIMM modules. But all the modules have a special number of pins also because the different operating voltage. So, in a way, all the four generation of RAMs aren't either forward or backward compatible.
So, suppose if you're having a motherboard which is supporting DDR3 RAM, then it'll not support either DDR2 or DDR4 RAM. So, the DIMM modules which are available during this form factors are used inside the desktop or pc . But if you see inside the laptop the formfactor of this DIMM module is sort of compact. And it's referred to as the SO-DIMM or just smalloutline DIMM Modules. So, if you see the various generation of SO-DIMMs, it's having a special number of pins also because the different operatingvoltages.
Now, thus far whatever discussion that we carriedout, we had assumed that this RAM is employed on the either pc or laptop. But this RAM is additionally categorized supported the applications during which it's getting used . So, the dynamic RAMs which are used insidethe mobile or smartphones are referred to as the mobile DDR or Low Power DDR. So, these Low Power DDR RAMs also are havingdifferent generations. ranging from LPDDR1 up to the LPDDR4. So, if you see the 2017 flagships they areoperated on this LPDDR4x RAM. So, LPDDR RAMs are optimised for the low powerconsumption. Because these RAMs are used inside the smartphonewhich has alittle amount of battery. So, this sorts of RAM has got to be optimisedbased on the facility consumption. So, the operating voltage of this LPDDR RAMis less compared to the DDR RAMs which are used inside the desktop and therefore the laptops. Similarly, the RAMs which are used for thegraphics cards is understood because the graphics DDR or just GDDR.
Now, as this Graphical DDR is employed for the multimedia applications, therefore the amount of knowledge that must be handled is sort of more. So, that's a reason, this sort of GDDR RAMsis more bandwidth compared to the desktop and therefore the laptop memories.
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