Hi all; Samsung PC1066 may be 35ns tRCD -- incompatible with the 850E, which is probably why no one is making a big deal out of it.
Rambus has renamed PC1066 to be "RIMM2100". It's specified in two access times, 32ns and 35ns, in ECC and non ECC as follows:
Organization I/O Freq tRAC(ns)
x16 1066 -35
x16 1066 -32
x18 1066 -35
x18 1066 -32
rdram.com
These same row access times also apply to the RIMM4200s:
rdram.com
1066MHz RDRAM chips are available with -30, -32 and -35 speeds:
rdram.com
So what's the difference in the timing restrictions between these three memory types? If you look through the above data sheet you find the following parameters with differences between various speeds, where I've bolded values that are largest (i.e. slowest, and therefore the least compatible) for a given row:
1066 1066 1066 800 800 600
Parameter -30 -32 -35 -40 -45 -53 Max Units
--------- ---- ---- ---- ---- ---- ---- ----- ------
tRC 28 28 32 28 28 28 -- tCYCLE
tRAS 20 20 22 20 20 20 64uS tCYCLE
tRP 8 8 10 8 8 8 -- tCYCLE
tRCD 7 9 9 7 9 7 -- tCYCLE
tCAC 8 8 9 8 8 8 12 tCYCLE
tRDP 4 4 5 4 4 4 -- tCYCLE
tRTP 4 4 5 4 4 4 -- tCYCLE
rdram.com
You can tell that 1066-35 is a rather unique beast. What's different about it is that it's timing numbers are incompatible with the 850, and very probably also the 850E. I think it is highly likely that Intel didn't spin the 850 for the 850E, but instead simply tuned the process to increase the clock rates by 33%. This means that the 850E can't support the 1066-35 speed grade of RDRAM. This is the only explanation I can think of for the fact that Intel has not yet validated any 800-45 RDRAM for the 850E, but have validated lots of 800-40. See #reply-17414166 for the details, including calculations and links.
Also note that the parameters for PC800-45 are exactly identical to the parameter for PC1066-32, and the parameters for PC800-40 are identical to the parameters for PC1066-30. From this I conclude that if Intel does support PC1066 on the 850E, it will be with the PC1066-32 and PC1066-30 speeds.
Samsung hasn't released any data sheets for PC1066 (RIMM2100) or RIMM4200. Nor have they released any data sheets for 1066MHz RDRAM chips. But they have given a clue as to their future plans in their part decoder. The problem is that the parts decoder for PC1066 includes -35 but no -32 or -30 parts:
15~16. tRAC(Row Access Time) & Speed
00 : for Continuity Module
K7 : 45ns/711Mbps(356MHz)
M9 : 35ns/1066Mbps(533MHz)
G6 : 53.3ns/600Mbps(300MHz)
K8 : 45ns/800Mbps(400MHz)
DS : DAISY CHAINf MDL
samsungelectronics.com
This means that the PC1066 modules are for a chipset other than the 850E. My conclusion is that they are for some of the NPU design wins that Rambus has, and possibly the SiS RDRAM chipset that is due out later this year. This explains why there is no PC1066 for sale only weeks before Intel releases the 850E. The SiS chip isn't ready yet, and industry doesn't buy RIMMs off of pricewatch.
-- Carl
P.S. The above post may give some people a clue about what digital design with DRAM is like. You look for compatibility relationships and try to support as much as possible with the least effort. Intel doesn't look like they're trying so hard anymore. |
