Doesn't DDR 800 run at 400 MHz?

PhilsComputerLab wrote:

Doesn't DDR 800 run at 400 MHz?

Winner.

SquallStrife wrote:

PhilsComputerLab wrote:

Doesn't DDR 800 run at 400 MHz?

Winner.

so DDR2 800 MHZ Doesnt run at 800MHZ?

TheAbandonwareGuy wrote:

SquallStrife wrote:

PhilsComputerLab wrote:

Doesn't DDR 800 run at 400 MHz?

Winner.

so DDR2 800 MHZ Doesnt run at 800MHZ?

That's ddr for you. 800mhz is its evicted clock rate.

https://en.m.wikipedia.org/wiki/Multi-channel … el_architecture

Yep, it would seem im an idiot 🤣

Jade Falcon wrote:

That's ddr for you. 800mhz is its evicted clock rate.

https://en.m.wikipedia.org/wiki/Multi-channel … el_architecture

That link is about dual-channel DDR, which doubles the effective data rate again. Not the reason that DDR2-800 runs at 400MHz.

OP, the 800 in DDR2-800 is MT/s, not MHz. MT/s is Mega Transfers/second.

Single data rate synchronous DRAM (SDR SDRAM) runs, as the name suggests, synchronously with the CPU's frontside bus. It achieves one transfer per clock, so at 133MHz, you get 133MT/s.

Double data rate SDRAM (DDR SDRAM) doubles the amount of data transferred per clock cycle, by transferring data on both the leading and trailing edges of the clock signal. Thus, with a FSB speed of 133MHz, you get 266MT/s, and hence DDR-266.

Or as in this case, 400MHz yielding 800 MT/s.

I had the same confusion when I got my DDR3 system together. It's akin to the idiotic megabit/byte thing for hard drives.

I always said that DDR was a big marketing scam that only serves to confuse people. CPUs and memory should be advertised at their actual clock rates. HDDs should also be advertised with their actual formatted capacities. None of this 1,000,000 bytes = 1MB bullshit, or how 1GB is defined as 1,000,000 "MBs".

hey... doesn't ddr2-800 run with 200mhz clock just like ddr-400? it performs 4 transfers in a clock cycle, therebye 200*4 transfers in a second.

noshutdown wrote:

hey... doesn't ddr2-800 run with 200mhz clock just like ddr-400? it performs 4 transfers in a clock cycle, therebye 200*4 transfers in a second.

Um, no. All DDR variants (DDR, DDR2, DDR3 etc) perform 2 transfers per external clock cycle, hence "double data rate". The differences between generations of DDR are minor (timings, prefetch queue depth, higher FSB etc)

Anonymous Coward wrote:

I always said that DDR was a big marketing scam that only serves to confuse people. CPUs and memory should be advertised at their actual clock rates. HDDs should also be advertised with their actual formatted capacities. None of this 1,000,000 bytes = 1MB bullshit, or how 1GB is defined as 1,000,000 "MBs".

Something I noticed with modern graphics cards. Memory throughput using "compressed" data 😀

Yup, that reminds of the data rate of analogue modems (baud vs bit/s).
Manufacturers were quite optimistic regarding the actual speed of their modems..

SquallStrife wrote:

That link is about dual-channel DDR, which doubles the effective data rate again. Not the reason that DDR2-800 runs at 400MHz. […]
Show full quote

Jade Falcon wrote:

That's ddr for you. 800mhz is its evicted clock rate.

https://en.m.wikipedia.org/wiki/Multi-channel … el_architecture

That link is about dual-channel DDR, which doubles the effective data rate again. Not the reason that DDR2-800 runs at 400MHz.

OP, the 800 in DDR2-800 is MT/s, not MHz. MT/s is Mega Transfers/second.

Single data rate synchronous DRAM (SDR SDRAM) runs, as the name suggests, synchronously with the CPU's frontside bus. It achieves one transfer per clock, so at 133MHz, you get 133MT/s.

Double data rate SDRAM (DDR SDRAM) doubles the amount of data transferred per clock cycle, by transferring data on both the leading and trailing edges of the clock signal. Thus, with a FSB speed of 133MHz, you get 266MT/s, and hence DDR-266.

Or as in this case, 400MHz yielding 800 MT/s.

Wops some how I thinker the wrong one. I'll get the right one tonight.

noshutdown wrote:

hey... doesn't ddr2-800 run with 200mhz clock just like ddr-400? it performs 4 transfers in a clock cycle, therebye 200*4 transfers in a second.

What you're describing is somewhat like QDR SDRAM, though in practice it's a little different than the name suggests.

Anonymous Coward wrote:

I always said that DDR was a big marketing scam that only serves to confuse people. CPUs and memory should be advertised at their actual clock rates. HDDs should also be advertised with their actual formatted capacities. None of this 1,000,000 bytes = 1MB bullshit, or how 1GB is defined as 1,000,000 "MBs".

It's what I hated about the whole MBits marketing of 16-bit era gaming. 🙁