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Technology Stocks : Rambus (RMBS) - Eagle or Penguin -- Ignore unavailable to you. Want to Upgrade?

To: grok who wrote (26056)	7/31/1999 9:45:00 AM
From: John Walliker	Read Replies (4) \| Respond to of 93625

KZNerd, PC200 is the first step in DDR. It is just 100 MHz double pumped. Then comes PC266 which is 133 MHz double pumped. Beyond that is DDR-II which will increase frequencies to 200 to 250 MHz and data rates to twice that. This is the natural evolution of the non-rambus dram world. It doesn't require that electrons shoot through wires faster or cause additional heat over rambus. The use of the word "just" glosses over a much harder problem than most people appreciate. One of the reasons why there is a time delay between data transfers is that the signals on the interconnection bus oscillate backwards and forwards between any discontinuities in characteristic impedance - especially from the ends but also from the individual chips, connectors and even bends in the printed circuit traces. If a sufficient settling time is not allowed, the data will sometimes be corrupted. Rambus overcomes this by specifying a well-defined characteristic impedance throughout the system and terminating the bus with this impedance. If this is implemented properly, there are no reflections and very high transfer rates indeed are possible - much faster than those currently contemplated. Think of the difference between looking at an object through air versus through a stack of plates of dirty glass. In the future I expect to see a new Rambus chip package where the signals travel onto, through and off each chip in turn with the connections to the chip forming impedance matched transmission lines. This would allow transfer rates of many G bit/s per pin. It is also wrong to suggest that doubling the data rate will not increase the power consumption. In CMOS circuits power is dissipated as a result of charging and discharging circuit capacitances. If the rate of doing this is doubled then so is the power consumption (if the voltage stays the same). Another issue is that increasing the data rate of conventional RAM will considerably increase radio frequency emissions. Many aspects of the Rambus design minimise these. Yet another issue is that conventional clocking arrangements fail when the wavelength of the clock signal is of the same order as the dimensions of the conductors. Rambus overcomes this by using two clocks, one for each direction of signal travel. John