Question DDR4-3200/LPDDR4-4266 clarification

[Ivan Tuzikov]

Hello, everybody!

According to AMD - AMD Ryzen™ 7 4800H supports DDR4-3200/LPDDR4-4266.

I've read some article about IceLake RAM, that LPDDR4 is 16 bit, so dual channel gives only 64 bit in comparison with DDR4 64 bit where dual channel gives 128 bit. Is this true? Which combination is faster and how much GB/s can be achieved?

Official AMD https://www.amd.com/en/products/apu/amd-ryzen-7-4800h page does not give Max Memory Bandwidth number.

IMHO, this number is of great importance for integrated Vega7 graphic units.

Thanks in advance for clarification!

 

[taeioum]

I had no idea this was part of the change, but Wikipedia says the following about LPDDR4 as opposed to LPDDR3:

"Change from one 32-bit wide bus to two independent 16-bit wide buses".

Reading that, I don't think you should worry. I couldn't imagine that they'd go down in number of bits. There's no way that specs are deteriorating, everything's always improving, sometimes the "do more with less" type of thing. That being said, LPDDR isn't exactly made for max performance. If you're looking for performance, go with regular DDR SO-DIMMs.

 

[Ivan Tuzikov]

I've found this article: https://www.hardwaretimes.com/whats...ddr6-memory-gddr6-vs-gddr5-vs-ddr4-vs-lpddr4/

It says: "LPDDR4 is the mobile equivalent of DDR4 memory. Compared to DDR4, it offers reduced power consumption but does so at the cost of bandwidth. LPDDR4 has dual 16-bit channels resulting in a 32-bit total bus. In comparison, DDR4 has 64-bit channels. Therefore, LPDDR4 RAM halves the bus..."

"On the plus side, enhanced variants of the memory also allow 16n prefetch or 64 bytes per channel like GDDR6 memory. "

So, as we can see, LPDDR4266 operates at 2133 MHz.

IMHO, notebook manufacturers, Intel, AMD - mislead prospective buyers of laptops. They declare 3200 bus clock frequency for ddr4 notebook offerings and 4266 data transfer rate for LPDDR4 ultrabook offerings. So they mix together MHz with MT/s which is very misleading and disorientating. Most people would look at higher value and think that it is better. But in reality LPDDR4 4266 MT/s is effectively the same as DDR4 2133 MHz.

P.S. on Intel's Ark site there is Max Memory Bandwidth value for Comet Lake CPU's, but there is no any indication of Max Memory Bandwidth for IceLake CPU's. Maybe because 3733 MT/s gives LPDDR 1866 which is not good for marketing.

P.P.S. I am not a specialist, just a PC-user with 25 years of experience since 1995. Maybe I got all wrong?

I hope some DRAM-guru would clarify this memory issues.

Thanks in advance!

 

[Kevin Hake]

The missing detail here is that the new cpus support either dual-channel DDR4-3200 or quad-channel LPDDR4-4266. So yes, dual channel LPDDR4 would only be 64 bit, but as it is quad-channel it is 128-bits wide, same as the dual-channel DDR4 option.

So which has the higher bandwidth? According to wikichip, the quad channel LPDDR4 does:

This SoC features two memory controllers, each supporting DDR4 or LPDDR4x. This chip supports up to 64 GiB of dual-channel DDR4 memory with data rates of up to 3200 MT/s (51.2 GB/s) or up to 32 GiB of quad-channel LPDDR4x with data rates of up to 4266 MT/s (68.27 GB/s).

Looks like the trade-off is the LPDDR has only half the maximum capacity. And it's not clear how latency or average performance is different between the two options, but at least for me knowing the maximum bandwidth is actually higher for the LPDDR makes me comfortable with that option.

 

[Nahid070]

So which has the higher bandwidth? According to wikichip, the quad channel LPDDR4 does:
Looks like the trade-off is the LPDDR has only half the maximum capacity. And it's not clear how latency or average performance is different between the two options, but at least for me knowing the maximum bandwidth is actually higher for the LPDDR makes me comfortable with that option.

It's not way possible to get a 3200 mhz ddr4 this much speed! You literally doubled the bandwidth here! Even for lpddr5 the data path is half of ddr3 or ddr4. 32 bit for dual channel. So the bandwidth of latest lpddr5 6400 would be similar as ddr4 3200..

 

[KNIGHT K]

It's not way possible to get a 3200 mhz ddr4 this much speed! You literally doubled the bandwidth here! Even for lpddr5 the data path is half of ddr3 or ddr4. 32 bit for dual channel. So the bandwidth of latest lpddr5 6400 would be similar as ddr4 3200..

Okay, so the thing is like that. In PCs DDR4 TWO stick module would be dual channel, right? 4 sticks a quad channel. Now DDR5 would change all of that a tiny bit as every generation meaning DDR5 DUAL CHANNEL would equal to DDR4 QUAD Channel, because the bus would get halved and channels doubled, freq and latency alone don't really play any bigger role since it's pretty straight forward it's just doubles as every generation before.