Rambus Dynamic Random Access Memory (RDRAM ) is a type of synchronous DRAM which was developed by the U.S. company Rambus Corporation.

Principle of operation

The Rambus solution consists of three components: Rambus controller, Rambus Channel and RDRAM.

The Rambus architecture can manage multiple independent Rambus channel. The Channel Interface Rambus only contains a 16 - or 18 - bit ( ECC ) wide data bus. , The address bus has a width of 8 bits and has separate lines for the row and column control. Advantage: simultaneous, independent accesses to rows and columns are possible, while data from the previous command to be transmitted.

The Direct RDRAM ( DRDRAM ) use as DDR SDRAM both signal edges for data transmission. In the course of a simplified naming only the designation RDRAM is used today.

Each RDRAM IC has a data capacity of the channel. Compared with 64 -bit memory bus, but has to be correspondingly high, the timing of the channels in order to achieve competitive bandwidths.

In some architectures, the RDRAMs have installed in pairs and may not be used memory slots are terminated with a CRIMM.


The internal data transfer to a RDRAM memory matrix differs from the data width and clock rate of the channel significantly: Internally, a 128- bit wide data path ( 144 bit with ECC) is used with a clock frequency of 100 MHz. Thus, every 10 ns can be 128-bit transfer from and to the memory array - this corresponds to the channel transfer rate of 1.6 GB / s An internal RDRAM logic divides the data into 16 -bit packets before they are transferred via the I / O pins with the channel clock frequency of 800 MHz to the bus. Thanks to the full data width of the ICs, the data in connection with access not spread over all blocks, but are stored contiguously in a single chip. Disadvantage: the chips heat up with burst accesses strong, which requires additional cooling. Rambus modules are therefore provided with an additional heat sink, which is to provide sufficient heat dissipation. Since the temperature of the cooling plates can exceed 60 ° C in normal operation, is located on the modules a warning message, usually in the form of the warning sign " Beware of hot surface ".

Each channel can handle up to 32 hips RDRAM-C. Interleaving with overlapping Transfern between the chip and the RAM bus controller raises the efficiency of a continuous data stream. Add to this the high number of individual bank RDRAMs. Up to 16 banks per IC can execute commands in parallel and ensure high efficiency at heavy traffic on the bus.


Prior to the development of ' Direct Rambus ' with which this type of memory was only become wider known there was already the precursor Base Rambus and Concurrent Rambus, which were used in special graphics-intensive applications such as workstations and game consoles.

Problems in the mass market

With the appearance of the Pentium 4 ( Willamette core ) Intel clearly favored as the successor to RDRAM SDRAM. This was mainly because the chipsets for Pentium 4 exclusively offered RDRAM support. RDRAM was unlike SDRAM faster, but had a significantly higher power consumption, produced, consequently, a corresponding amount of waste heat and was sometimes more than twice as expensive as SDRAM. A PC system with an AMD Athlon processor and SDRAM had a similar performance to a Pentium 4 processor and RDRAM, but cost significantly less.

With the advent of DDR SDRAM systems for the Athlon these took the lead. Intel recognized the problems and now also offered support for DDR SDRAM. In this context, the weakness of the Pentium 4 revealed this was now in some cases significantly slower than in systems with RDRAM in systems with DDR - SDRAM. Shortly thereafter, however, Intel presented a revised version of the Pentium 4 before ( Northwood core ), which now had a much larger cache ( second level cache ). This processor could now easily compete with the AMD Athlon XP in a DDR SDRAM system, bringing the topic RDRAM had done well for Intel.

Away from the PC market was RDRAM use in the game consoles Nintendo 64 and PlayStation 2, as well as sporadically in graphics cards ( for example, by Cirrus Logic).


As the successor to Rambus XDR memory developed the which is used in the Playstation 3 and other devices with a Cell processor. The XDR technology offers several advantages compared to the GDDR standard. So are simpler boards are made possible and the bandwidth should be much larger. While GDDR5 uses a 4 × multiplier, XDR has an 8 × multiplier. The advanced XDR2 comes standard at 16 ×.