Next Generation RAM

RAM is one of the most crucial component in a PC. Sadly, it is also the most

neglected one. It comes in different makes, with different latency, bandwidth;

and now-a-days RAM catering to the budget conscious people; and to people who

want to overclock their RAM to attain maximum performance. But with DDR 2 RAM

available, and tweaked to the max, what's the next generation technology that

would replace it? Also what about the static RAM and RAM used in servers, where

are they heading? We look at the available RAM options, what you need to know

about them, alongwith the upcoming technologies that would replace current

generation RAM.

Static or dynamic RAM?



RAM is categorized mainly as Static or Dynamic RAM. The major difference between
the two is that dynamic RAM needs to be refreshed many times per second by the

processor or it loses all the stored data, whereas static RAM retains data even

it is not refreshed by the processor. The major benefit of static RAM is that it

doesn't create overhead on the CPU, by eliminating the need for refreshing

regularly. Up till now we have seen various avatars of both dynamic and static

RAM to fulfill the needs of the growing IT sector. 

The commonly known dynamic RAM are Fast page mode RAM , Extended Data

out RAM , Synchronous Dynamic RAM , Double Data Rate Synchronous

Dynamic RAM and Double Data Rate 2 Synchronous Dynamic RAM SDRAM> . The commonly known static RAM are Mobo cache, used in computers to

function as cache memory, and Quad data rate RAM (a form of static RAM), used in

switches and routers. What's coming? Well there are a couple of new

technologies, any of which can become the mainstream component for powering

future generation of computers.

The key trend in RAM over the past 4-5 years has been a huge increase in data transfer rates

RAM for Communications



QDR SRAM has been used in switches and routers for past 7
years and provides data rates above 200 MHz . The SRAM provides data throughputs

of 11Gbps as they use separate input and output ports for read and write and

these ports have separate differential clocks allowing for four words transfer

on each clock cycle. Various products from Cypress and Samsung are available.

QDRII+ RAM was announced last year along with DDR2+. These RAM have high

performance architecture and operate at speeds upto 500 MHz, which is more than

twice of what existing products offer. SRAM delivers a bandwidth of 72Gbps while

using a 165 pin FBGA (fine pitched ball grid array) package. These are used

mainly in the next generation of switches and routers to enhance communication

capabilities by giving the density and performance required to expand network

capabilities.

The return of RAMbus



RAMbus Incorporated is the manufacturer of RDRAM, which at one point of time was
considered a replacement for SDRAM. It formed an agreement with Intel to be the

primary memory technology of all Intel products. However, RDRAM was not able to

make a mark for itself due to various problems such as high latency, heat

emission and high cost of manufacturing. So, RDRAM faded away, but RAMbus did

not die and has come back with XDR DRAM. 

Elpida's XDR RAM chips use 90nm process technology to provide bandwidth of 8 Gbps

This new memory module has a high performance architecture based on the

RAMbus RDRAM. It improves on the high latency problem of RDRAM, significantly

improving bandwidth while reducing the number of ICs required. The XDR devices

will feature programmable on chip termination, adaptive impedance matching,

dynamic request scheduling and zero overhead refresh. Also, XDR uses Octal Data

Rate transfers to transfer eight bits of data per 400MHz clock cycle which

results in 6.4Gbps bandwidth speed for a 16bit bus instead of 3.2Gbps bandwidth

provided by a DDR RAM for a 64bit bus. Samsung and Elpida are already

manufacturing XDR RAM and now Qimonda has joined in to mass manufacture XDR RAM

for game consoles, set top boxes and PC graphics market. The Playstation 3 has

shipped with 256 MB module of XDR RAM onboard to achieve maximum performance,

whereas RAMbus has started development on XDR2 RAM with which they are targeting

8.0GHz data rates, enabling a single DRAM device with 16 Gbps of peak bandwidth.

Successor to DDR2



DDR3 SDRAM is the one that is the hot favorite of many and touted as the leader
of the next generation of RAM. DDR3 is based on 90nm fabrication technology and

would be using 'Dual gate' transistors to reduce leakage of current, leading

to almost 40% less power usage in comparison to DDR2. As DDR3 modules are

expected to transfer data at a clock rate of approximately 800 MHz instead of

400 MHz, the clock rate of DDR2, it is expected to attain up to 1600 MHz single

clock bandwidth as compared to 1066 MHz bandwidth of DDR2 RAM. Also the prefetch

buffer of DDR3 is 8-bit wide in comparison to 4-bit buffer available in DDR2,

which leads to double bandwidth and decreased heat production. A newly

introduced automatic calibration feature for the output buffer enhances the

ability to control the system timing budget during variations in voltage and

temperature. 

However DDR3 does have a disadvantage of having a higher CAS (column address

select) latency. But this can be overlooked, due to the higher bandwidth

provided by DDR3 memory modules. Intel has already announced that it would

develop the architecture to support DDR3 RAM when they become available late in

2007. AMD too has announced a joint venture with SimpleTech Inc, to get ready

for DDR3-based SDRAM, expected to be available by 2008. So, DDR3 has already

established itself as the successor to DDR2.

RAM for servers



Up till now, DDR2 RAM has been used in most of the servers, but things are

changing with the arrival of FB-DIMM RAM. It has already been adopted by Intel

for their latest Xeon 5000/5100 series servers, whereas AMD's new processors

based on the K8L architecture will have support for FB-DIMM RAM Even Apple is

using this RAM in its Mac Pro workstations. These RAM use an Advanced Memory

Buffer (AMB) between the memory controller and the memory module. Instead of the

parallel bus architecture used in DRAM, they use a serial architecture

connecting the memory controller and the AMB, which in turn allows for error

correction and more memory bandwidth than DDR2 and DDR3. The architecture also

allows for more memory width without an increase in the pin count; however it

suffers from a higher latency in memory request similar to that in DDR3. But

these provide the required bandwidth needed by servers and thus higher latency

can be overlooked. Additionally, GDDR3 memory is used in current generation

graphics cards to boost video performance. Recently ATI shifted onto GDDR4

memory in their X1950 series of graphics cards. There are talks of GDDR5 memory

being released in 2007, but this is yet to be confirmed from the manufacturers.

Overall, this year could be a defining stage for next generation RAM.