Ok, Crashman, granted you could fill and encyclopedia with what I don’t know about computers. I apologize for antagonizing my betters, but when I am struggling to understand something I become very obsessive and a little crazy.
400 and 800 are frequencies. Frequencies as in, times per second. NOT megabytes per second, times per second. Not gigabytes per second, but times per second.
I have already provided links on how to calculate bandwidth from memory speed but this is from an Intel white paper.
http://www.kingston.com/newtech/MKF_520DDRwhitepaper.pdf
Peak Bandwidth is calculated as:
Memory Speed x Number of bytes transferred per channel x Number of Channels
(its data rate) (8 Bytes or 64 bits) (one or two)
For PC3200, also known as DDR400, modules on a dual-channel motherboard,
Peak Bandwidth = (400 MHz) x (8 Bytes) x (2 Channels)
= 6400 Megabytes per second (MB/s)
or 6.4 Gigabytes per second (GB/s)
I presented the above calculation earlier in the thread which, I assume, is what you are objecting to. I may be ignorant of computers but I can do arithmetic. I don’t see where I confused frequency with bandwidth.
DDR400 in dual channel mode still has a 400MHz data rate, but it's on a 128-bit bus rather than a 64-bit bus
From the same white paper.
“Intel’s newest Pentium4 processors have front-side bus architectures operating at data
speeds of 533MHz and 800MHz. This translates to a peak data bandwidth of 4.2GB/s
(533MHz x 8 Bytes) and 6.4GB/s (800MHz x 8 Bytes) respectively”
800 MHz x 8 Bytes. That is a 64 bit or 8 byte font side bus. The board reads 128 bits at once from memory, but the data is transferred to the CPU at 64 bits per effective cycle.
OK, first of all, DDR400 is never 800. Second of all, it doesn't need to be.
Understood, this had always been my understanding. My confusion was because I misunderstood something pat wrote. When he said Qdr (quad data rate) he was referring to FSB. When I googled Qdr I only found links about memory. So, I thought, if Pat thinks DDR can run at quad data rate, maybe he knows and I don’t.
Using your definition this would be impossible. Using that definition of the FSB being the entire pathway between the CPU and RAM,
I never said the FSB was the entire pathway.
The FSB has been split for the entire 21st century. Using 20th century definitions, even if they've been poorly updated, would leave you more clueless than you already are. Since the FSB is split into two sides now, the CPU bus and RAM bus, you can have "asynchronous clocks".
If you don't believe me, google the term "asynchronous clocks" and see what you come up with.
I googled “asynchronous clocks”. In a synchronous system a timing signal is sent through the whole system to keep the components in sync. This heats up the board. Also, the system can only run as fast as its slowest component.
In an asynchronous system, each component has its own clock or no clock (frequency is determined by the width of the transistors and the speed of the current.) When a signal reaches a component, it is synchronized by various means.
Components on synchronous system can also run at different rates if the rates are multiples of the clock cycle - I.e. memory at 400 MHz, FSB at 800 MHz.
Asynchronous clocks have everything to do with synchronicity but nothing to do with frequency or bandwidth. The aggregate frequency of memory still must be less than or equal to FSB.
After NEW technology allowed the CPU and RAM clock speeds to be asynchonous, most industries have gone on to use the term "Front Side Bus" to refer ONLY to the bus beteen the CPU and chipset
I was never confused on this issue. You could say FSB is the link between the memory controller and the CPU. But, here we have the thrust of the issue. On a single channel DDR400 system the FSB runs at 200 MHz and makes 2 transfers per cycle. 2 reads per cycle is all the memory can provide. This is 400 MHz effective. Since the CPU’s FSB side must run at 200 MHz and the Pentium can handle 4 transfers per cycle, the CPU must be rated 800 MHz FSB.
But the Front Side Bus is not on the CPU it is on the motherboard. The memory controller feeds 2 transfers per cycle to the CPU at 200MHz. That is a 400 MHz FSB. The CPU could handle twice that rate, but the board only supplies 400 MHz effective and a bandwidth of 3200 MB/s.
It seems to me the specs for the board should reflect the properties of the board, not the CPU. They should say 400 MHz FSB but requires a processor rated for 800 MHz FSB.