Following the purchase of an almost immaculate N64, I've renewed my interest in this little console. We know a lot about the CPU and the RCP. The Rambus memories in it, however remains a rather undeveloped subject. Even in the retro-modding forums all the info I could gather is that they are not tolerant to overclock and that, apparently, the N64 can 'recognize' up to 16Mbytes automatically at boot.
Apparently, Nintendo used in the N64 an early version of Rambus RDRAM made by NEC: the uPD488170L. It's a 16+2 Mbit chip with a 9 bit datapath, 250MHz double data rate bus. There were two of these chips in a N64 and they were daisy chained. (On a side note, I found out that there was even an earlier version of this chip with a voltage supply of 5V and realized in 1992!). 16/18Mbit RDRAM was all you could buy in 1996/7 and they were used also in some VGAs of the period (Cirrus Logic Laguna, a version of Chromatic Research MPACT!, SGI workstation cards...).
Some N64 units had these chips marked as "Nintendo RAMBUS18-NUS" but there are also motherboards using chips with the true name of the manufacturer (NEC) and the product code.
Sometime in 1998, Nintendo switched to a single 32/36 Mbit chip (the extra 'Mbits' are available for parity). One of these chips was also included in the 'expansion pak', the little plastic cartridge that was required to use 'hi res' graphics (640x480 vs 320x240) in certain games. Unlike the early 16/18Mbits memories, there is absolutely no info about this chip. The info I could gather is that these appear to be tolerant to overclock possibly being PC600 class. All the major RDRAM manufacturers started to supply PC600 64/72Mbits chips realized with a 0.25u process in 1998 but I couldn't find a single source or datasheet on a 32/36mbit variety. These chips still shows up from time to time from Chinese sources with Nintendo markings. Are they leftovers or removed from board? The fact that some surplus stock still exists after all these years is fascinating... Anyway, some people successfully replaced the two 16/18Mbit chips inside the early units with a pair of these to have an 8MB console. Adding an expansion pak brings the total amount of memory to 12MB and the memory controller is still able to recognize all of them (some say up to 16MB are recognized by virtue of using certain expansion paks with room for 2 chips). Of course no game uses more than 8MB at a time, but it's a nice discovery that the N64 could have been developed into an even more powerful console. Image in it had launched with 16MB of RAM! Cartrdige space would have still been a problem but the extra memory could have been used for procedurally generated content (ie pre computed animations... the geometry processor inside the RCP sometimes was not able to cope with everything being thrown at it).
By the way, in somebody finds a datasheet for this chip, it would be nice of him to share it with me! They are marked RDRAM36-NUS 9937KU653 but this is just a Nintendo internal code, so it's not possible to determine the true manufacturer of said chip.
Apparently, Nintendo used in the N64 an early version of Rambus RDRAM made by NEC: the uPD488170L. It's a 16+2 Mbit chip with a 9 bit datapath, 250MHz double data rate bus. There were two of these chips in a N64 and they were daisy chained. (On a side note, I found out that there was even an earlier version of this chip with a voltage supply of 5V and realized in 1992!). 16/18Mbit RDRAM was all you could buy in 1996/7 and they were used also in some VGAs of the period (Cirrus Logic Laguna, a version of Chromatic Research MPACT!, SGI workstation cards...).
Some N64 units had these chips marked as "Nintendo RAMBUS18-NUS" but there are also motherboards using chips with the true name of the manufacturer (NEC) and the product code.
Sometime in 1998, Nintendo switched to a single 32/36 Mbit chip (the extra 'Mbits' are available for parity). One of these chips was also included in the 'expansion pak', the little plastic cartridge that was required to use 'hi res' graphics (640x480 vs 320x240) in certain games. Unlike the early 16/18Mbits memories, there is absolutely no info about this chip. The info I could gather is that these appear to be tolerant to overclock possibly being PC600 class. All the major RDRAM manufacturers started to supply PC600 64/72Mbits chips realized with a 0.25u process in 1998 but I couldn't find a single source or datasheet on a 32/36mbit variety. These chips still shows up from time to time from Chinese sources with Nintendo markings. Are they leftovers or removed from board? The fact that some surplus stock still exists after all these years is fascinating... Anyway, some people successfully replaced the two 16/18Mbit chips inside the early units with a pair of these to have an 8MB console. Adding an expansion pak brings the total amount of memory to 12MB and the memory controller is still able to recognize all of them (some say up to 16MB are recognized by virtue of using certain expansion paks with room for 2 chips). Of course no game uses more than 8MB at a time, but it's a nice discovery that the N64 could have been developed into an even more powerful console. Image in it had launched with 16MB of RAM! Cartrdige space would have still been a problem but the extra memory could have been used for procedurally generated content (ie pre computed animations... the geometry processor inside the RCP sometimes was not able to cope with everything being thrown at it).
By the way, in somebody finds a datasheet for this chip, it would be nice of him to share it with me! They are marked RDRAM36-NUS 9937KU653 but this is just a Nintendo internal code, so it's not possible to determine the true manufacturer of said chip.