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DDR1 SDRAM, has been superseded by DDR2 SDRAM, DDR3 SDRAM and DDR4 SDRAM.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 It superseded the original DDR SDRAM
specification, and is superseded by DDR3 SDRAM.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.
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