TYPES OF RAM

TYPES OF RAM

There are two main types of RAM

        1)    DRAM (Dynamic Random-Access Memory)

        2)    SRAM (Static Random-Access Memory)

        1)    DRAM (Dynamic Random-Access Memory)

        -       Dynamic random-access memory (DRAM) is a type of memory that is typically used for data or program code that a computer processor needs to function. DRAM is a common type of random access memory (RAM) used in personal computers, workstations and servers.

        2)    SRAM (Static Random-Access Memory)

        -       Static random-access memory is a type of semiconductor random-access memory that uses bistable latching circuitry to store each bit. SRAM exhibits data remanence, but it is still volatile in the conventional sense that data is eventually lost when the memory is not powered.

What is DDR1, DDR2, DDR3 & DDR4?

DDR1

        -          DDR SDRAM (Double Data Rate Synchronous Dynamic Random-Access Memory), officially abbreviated as DDR SDRAM, is a DDR (DOUBLE DATA RATE) SDRAM (Synchronous Dynamic Random-Access Memory) class of memory integrated circuit used in computer. DDR SDRAM, also retroactively called DDR1 SDRAM, has been superseded by DDR2 SDRAM, DDR3 SDRAM and DDR4 SDRAM.

        -          Double Data Rate-SDRAM, or simply DDR1, was designed to replace SDRAM.

        -          DDR1 was originally referred to as DDR-SDRAM or simple DDR. When DDR2 was introduced, DDR became referred to as DDR1. Names of components constantly change as newer technologies are introduced.

        -          The principle applied in DDR is exactly as the name implies “double data rate”. The DDR actually doubles the rate data is transferred by using both the rising and falling edges of a typical digital pulse. Earlier memory technology such as SDRAM transferred data after one complete digital pulse. DDR transfers data twice as fast by transferring data on both the rising and falling edges of the digital pulse. Look at figure below.

DDR2

        -          Double Data Rate 2 Synchronous Dynamic Random-Access Memory, officially abbreviated as DDR2 SDRAM, is a double data rate synchronous dynamic random-access memory interface. It superseded the original DDR SDRAM specification, and is superseded by DDR3 SDRAM.

        -          DDR2 is the next generation of memory developed after DDR.

        -          DDR2 increased the data transfer rate referred to as bandwidth by increasing the operational frequency to match the high FSB (front-side bus) frequencies and by doubling the prefetch buffer data rate.

        -          DDR2 is a 240 pin DIMM design that operates at 1.8 volts. The lower voltage counters the heat effect of the higher frequency data transfer.

        -          DRR operates at 2.5 volts and is a 188 pin DIMM design.

        -          DDR2 uses a different motherboard socket than DDR, and is not compatible with motherboards designed for DDR.

        -          The DDR2 DIMM (Dual In-line Memory Module) key will not align with DDR DIMM (Dual In-line Memory Module) key. If the DDR2 is forced into the DDR socket, it will damage the socket and the memory will be exposed to a high voltage level. Also be aware the DDR is 188 pin DIMM (Dual In-line Memory Module) design and DDR2 is a 240 pin DIMM design.

What is FSB?

       -          A FRONT-SIDE BUS is a computer communication interface that was often used in Intel-chip-based computers during the 1990s and 2000s. The competing EV6 bus served the same function for AMD CPUs. Both typically carry data between the central processing unit and a memory controller hub, known as the northbridge.

DDR3

        -          Double Data Rate 3 Synchronous Dynamic Random-Access Memory, officially abbreviated as DDR3 SDRAM, is a type of synchronous dynamic random-access memory with a high bandwidth interface, and has been in use since 2007.

        -          DDR3 was the next generation memory introduced in the summer of 2007 as the natural successor to DDR2.

        -          DDR3 increased the pre-fetch buffer size to 8-bits an increased the operating frequency once again resulting in high data transfer rates than its predecessor DDR2. In addition, to the increased data transfer rate memory chip voltage level was lowered to 1.5 V to counter the heating effects of the high frequency. By now you can see the trend of memory to increase pre-fetch buffer size and chip operating frequency, and lowering the operational voltage level to counter heat.

        -          The physical DDR3 is also designed with 240 pins, but the notched key is in a different position to prevent the insertion into a motherboard RAM socket designed for DDR2.

        -          DDR3 is both electrical and physically incompatible with previous versions of RAM. In addition to high frequency and lower applied voltage level, the DDR3 has a memory reset option which DDR2 and DDR1 do not.

        -          The memory reset allows the memory to be cleared by a software reset action. Other memory types do not have this feature which means the memory state is uncertain after a system reboot. The memory reset feature insures that the memory will be clean or empty after a system reboot. This feature will result in a more stable memory system. DDR3 uses the same 240-pin design as DDR2, but the memory module key notch is at a different location.

DDR4

        -          DDR4 is a new memory standard designed to eventually replace DDR3. While it’s true that when running at the JEDEC (Joint Electron Device Engineering Council) specified speeds of 2133MHz and 2400MHz DDR4’s higher latencies may produce slightly lower performance clock-for-clock than DDR3, DDR4 is designed to reliably run at much higher speeds that more than offset the increased latency.

       -          In virtually every way, DDR4 is superior to DDR3: it’s capable of being much faster, more efficient, more scalable, and even more reliable. As for cost, much like the transitions to DDR, DDR2, and DDR3, DDR4 will become progressively cheaper as economies of scale take effect.

       -          Physically, a DDR4 module, or DIMM (Dual In-line Memory Module), is very similar to a DDR3 DIMM.

       -          DDR4 can use a slightly taller printed circuit board and ups the pin count from DDR2 and DDR3’s 240 pins to 288. The key notch (to ensure the DIMM is not improperly installed) is also in a different place, and the overall shape of the connector has a slight “V” contour to aid installation.

       -          Architecturally, DDR4 is designed to operate at higher speeds and capacities with lower voltage and adds reliability features not present in DDR3.

       -          Double Data Rate 4 Synchronous Dynamic Random-Access Memory, officially abbreviated as DDR4 SDRAM, is a type of synchronous dynamic random-access memory with a high bandwidth interface.

-         DDR4 Improvements

  

              1)  Transfer Rate

2)      Data Integrity

3)      Power Consumption

4)      Memory Size

5)      Command Encoding

-         DDR Bandwidth Growing Over Time

Why Do We Need DDR4?

        -          When DDR4 is introduced, the initial 2133MHz and 2400MHz speeds will be accompanied by another increase in latency, just as each previous memory technology transition has been. These speeds are essentially the top of the ladder for DDR3, though; while DDR3 kits can be obtained at speeds as high as 3200MHz, ICs capable of performing at those levels are extremely rare.

        -          Meanwhile, DDR4 is expected to scale well beyond 3200MHz. What DDR4 offers is scalability for the future: individual DIMM densities start at 4GB and 8GB and are expected to scale to 16GB in 2015.

        -          Bandwidth is also capable of scaling up tremendously. 2666MHz DDR3 isn’t especially common right now; it operates outside of JEDEC spec and requires carefully selected ICs, yet already situations exist that demonstrate a need for increased bandwidth beyond that speed.

        -          DDR4 comes out of the gate at 2400MHz, with 2666MHz, 2800MHz, and 3000MHz SKUs already planned.

        -          Finally, DDR4 operates at a nominal 1.2V and scales up to 1.35V, a reduction in operating power from DDR3’s 1.5V standard and 1.65V mainstream high-performance spec. Power efficiency has become increasingly important with each subsequent generation of CPU and GPU architecture from Intel, AMD, and NVIDIA, and DDR4 helps to enable that.

Compare DDR Prefetch, Chip Voltage and Data Rates for Motherboard FSB (front-side bus).

GENERATION	PREFETCH BUFFER	VOLTAGE LEVEL	FSB DATA RATES EXPRESSED (Mhz)
DDR1	2-Bits	2.5 V	200,266,333,400
DDR2	4-Bits	1.8	400,533,677,800
DDR3	8-Bits	1.5	800,1066,1330,1600

Future of Memory DDR5?

        -          Increased speed

        -          Higher density

        -          Lower voltage

        -          More focus here in coming future as mobile device market increases.