Intel’s solution to the memory bottleneck has been Rambus Technologies’ RDRAM
(Rambus DRAM). Rambus is an entirely new design in memory technology, centered
around extremely high operating frequencies--RDRAM operates at an astonishing
400 MHz. To attain such high clock speeds, however, RDRAM features a slimmer bus
than current SDRAM. As opposed to SDRAM’s 64-bit bus, RDRAM operates on a slim
16-bit bus. This incongruency in bus-width, however, means that an
RDRAM-supporting chipset must be designed differently, and will not be
compatible with an SDRAM chipset, without some form of translation such as
Intel’s MTH. Further adding to RDRAM’s impressive numbers is its ability to
transfer data on both the rising and falling edges of the clock cycle. Given all
that, the theoretical maximum bandwidth provided by RDRAM is as follows:
(400MHz Operating Speed) x (16-bit Bus) x (2 Rising & Falling Edge) / (8
bits per byte) = 1600MB/s available bandwidth.
The numbers speak for themselves--RDRAM is capable of providing twice as much
bandwidth as PC100 SDRAM, and 50% more than even PC133 SDRAM. Further adding to
these impressive numbers is RDRAMs extremely high efficiency. Simply put, RDRAM
is a very streamlined, effective memory architecture. Hyundai has estimated
RDRAMs bus effectiveness to be as high as 85%, compared to SDRAM’s 75%. So,
RDRAM is the perfect solution, right? Wrong.
The primary, and most important concern with RDRAM at present is simply cost.
Yields thus far have been less than impressive, which drives up the cost of
RDRAM. As well, RDRAM is a proprietary technology, unlike SDRAM, which means
that any third party memory manufacturer who wishes to produce RDRAM is forced
to pay royalties to Rambus. Furthermore, due to RDRAM’s completely new design,
production would require retooling of current memory manufacturers’ fab plants,
an expensive process. Those factors, coupled with some early problems with RDRAM
(read: i820 fiasco), have resulted in most major memory manufacturers being
somewhat reluctant to hop onto the RDRAM bandwagon. At present, 128 MB of RDRAM
will set a user back close to $1000, which is tough to swallow.
And price is not the only concern with RDRAM--many have voiced worries about
its higher latency. The smaller 16-bit bus, while allowing for higher throughput
speeds, forces a slight serialization of the commands. Because of this, the
handful of applications out there that require very rapid access to small bits
of data from different locations will actually suffer a slight decrease in
performance when used with RDRAM. Fortunately, the majority of software in
existence at the moment will benefit from the higher continuous speeds RDRAM
brings to the table.
