Feeds

Wham, bam, thank you RAM

Reg reader on the job

  • alert
  • submit to reddit

The Power of One eBook: Top reasons to choose HP BladeSystem

AMD and Intel - who said what?

We're obliged to Charlie Demerjian for this mini-thesis on RDRAM vs DDRRAM. I suggest you make a nice cup of tea before wading in:

I assume you already know this, but in case you have ANY doubts, here is the answer for the reader who wrote in about the RDRAM vs DDRRAM.

Anyways, lets go on to the technical nitty gritty. PC800 rambus runs at 400MHz, double pumped, on a 16 bit (2 byte) wide bus. Overall, the bandwidth is 400MHz*2*2bytes, or 1600MBps, or 1.6GBps. PC700 and PC600 are slower, although neither runs at the speed the names would lead you to believe. Toms Hardware (www.tomshardware) had two excellent articles on rambus a while ago. I highly recommend that anyone even vaguely interested or confused read these, they are a good starting point.

DDR runs at 100 or 133MHz, double pumped, 64 bits (or 8 bytes) wide. 100MHz*2*8bytes=1600MBps, whole 133MHz*2*8bytes=2100MBps. The magic is that DDR transfers 4 times as much information per clock, while rambus runs at 4 times the clock rate.

On paper this is an even match, but there are several things that skew the arguement in favor of DDR. The first is cost. Go to www.pricewatch.com and look around. Since we are not argueing cost here, I will let this one slide for now. Next is latency. The time it takes to read a single byte at random is MUCH higher on a rambus system than on a DDR system. This is a fundamental flaw of rambus. The P4 can hide it fairly well, but you can apply those same trics to DDR is you so choose.

Because DDR's latency is fairly low, there hasn't been much call to do so. All things being equal, in random reads, DDR will most likely beat rambus. After latency comes pin count. Rambus wins this one handily. The number of pins needed to implement a rambus channel is about 1/4 of the pins needed to run a DDR channel. The more pins, the more money it costs to design and manufacture the motherboard. This makes rambus mobos cheaper right? Well, that leads us to the last point, which is speed (although a different speed than the numbers above). Since rambus runs its memory at 3 to 4 times the speed of DDR (400 vs 100 or 133), it is much harder to design. Much MUCH harder. Ask the people who designed the intel i820 chipsets, or the motherboards that use it (*cough* 2 rimms per channel *cough*).

When a company like intel repeatedly recalls, delays, and eventually kills of thier flagship product, you have to wonder about that product.. Intel, for all the run I make of it, probably has one of the finest and deepest pools of engineering talent available in the semiconductor industry. If they can't figure it out, there have to be problems. DDR motherboards are much less of a problem, although still not easy.

Overall, DDR has more bandwidth, less latency, and is easier to design for. The only way rambus is faster is because some motherboards use 2 channels (i840, i850) for twice the raw bandwidth. If you implemented a dual DDR chipset, it would be MUCH faster than a rambus mobo (single or dual)

Reducing security risks from open source software

More from The Register

next story
Motorist 'thought car had caught fire' as Adele track came on stereo
'FIRE' caption on dashboard prompts dunderheaded hard shoulder halt
Japanese artist cuffed for disseminating 3D ladyparts files
Printable genitalia fall foul of 'obscene material' laws
Carlos: Slim your working week to just three days of toil
'Midas World' vision suggests you retire later, watch more tellie and buy more stuff
Brit Rockall adventurer poised to quit islet
Occupation records broken, champagne corks popped
Accused! Yahoo! exec! SUES! her! accuser!, says! sex! harassment! never! happened!
Allegations were for 'financial gain', countersuit claims
Yahoo! Japan! launches! service! for! the! dead!
If you're reading this email, I am no longer alive
Plucky Rockall podule man back on (proper) dry land
Bold, barmy Brit adventurer Nick Hancock escapes North Atlantic islet
NSA man: 'Tell me about your Turkish connections'
Spooks ask Dabbsy to suggest a nice hotel with pool
prev story

Whitepapers

Designing a Defense for Mobile Applications
Learn about the various considerations for defending mobile applications - from the application architecture itself to the myriad testing technologies.
How modern custom applications can spur business growth
Learn how to create, deploy and manage custom applications without consuming or expanding the need for scarce, expensive IT resources.
Reducing security risks from open source software
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Consolidation: the foundation for IT and business transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.