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Comment by hydroreadsstuff | Hacker News Reader

How do they get 200/400GB per second RAM bandwidth? Isn't that like 4/8 channel DDR5. 4/8 times as fast as current Intel/AMD CPUs/APUs? (E.g. https://www.intel.com/content/www/us/en/products/sku/201837/... with 45.8GB/s)

Laptop/desktop have 2 channels. High-end desktop can have 4 channels. Servers have 8 channels.

How does Apple do that? I was always assuming that having that many channels is prohibitive in terms of either power consumption and/or chip size. But I guess I was wrong.

It can't be GDDR because chips with the required density don't exist, right?

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It's LPDDR5, which maxes out at 6.4Gbit/s/pin, on a 256bit/512bit interface.

It's much easier to make a wider bus with LPDDR5 and chips soldered on the board than with DIMMs.

I hope we will see this on more devices. This is a huge boon to performance.

Might even forebode soldering RAM onto packages from here on out and forever.

Steamdeck will probably have a crazy 100gb/sec ram b/w. twice of current laptops and desktops.

Steamdeck is 88 GB/s using quad channel.

You aren't wrong, Apple is able to do this because implementing LPDDR is much more efficient from both a transistor and power consumption point of view, and is actually faster too. The tradeoff is you can't put 8 or 16 dram packages on the same channel like you can with regular DDR, which means that the M1 Max genuinely has a 64 GB limit, while a DDR system with the same bandwidth would be 1 TB. Fortunately for Apple there isn't really a market for a laptop with a TB of RAM.

They are using LPDDR5.

Not the usual DDR5 used in Desktop / Laptop.

DDR5 isn't common yet.

DDR4 is the common desktop/laptop chip. LPDDR5 is cell-phone chip, so its kinda funny to see a low-power RAM being used in a very wide fashion like this.

Don't cell phones sell more than desktops, laptops, and servers? Smartphones aren't a toy: they are the highest volume computing device.

They are also innovating with things like on-chip ECC for LPDDR4+, while desktop DDR4 still doesn't have ECC thanks to Intel intentionally gimping it for market segmentation.

Well sure. But that doesn't change the fact that DDR5 doesn't exist in any real numbers.

LPDDR5 is a completely different protocol from DDR5 by the way, just like GDDR5 is completely different from DDR3 it was based on. LPDDR3 was maybe the last time the low-power series was something like DDR3 (the mainline).

Today, LPDDR5 is based on LPDDR4, which diverged significantly from DDR4.

> They are also innovating with things like on-chip ECC for LPDDR4+

DDR5 will have on-chip ECC standard, even unbuffered / unregistered.

That sound like HBM2, maybe HBM3 but that would be the first consumer product to include it afaik.

Basically the bus is really large, and the memory dies must be really close to the main processing die. Those memory were notably on the RX Vega from AMD, and before that on the R9 Fury.

https://en.m.wikipedia.org/wiki/High_Bandwidth_Memory

If that were the case you could probably see an interposer. And I think the B/W would be even higher.

And the price would be even higher.

If it was HBM it would have considerably higher bandwidth. A single HBM2E stack is 16GB at 460GBps, at 64GB that's 1.8TBps of bandwidth.

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