[erik]

The M1's bandwidth is possible because Apple uses high end LPDDR ram and a memory controller with a lot of channels. They aren't doing anything exotic.

Consumer PCs don't match this bandwidth because DDR DIMMs generally aren't as fast as LPDDR. Plus AMD & Intel limit their mainstream consumer CPUs to two memory channels, both for cost savings and to segment the market.

[vitus]

> Consumer PCs don't match this bandwidth because DDR DIMMs generally aren't as fast as LPDDR.

What about LPDDR (low-power DDR) allows it to be faster? And, by faster, do you mean lower latency? higher clock rates -> higher throughput? This is unintuitive to me.

My impression is that lower power means that you can't sustain higher clocks as readily (in fact, when overclocking RAM, it's common to increase voltage in the interest of stability).

I can't find anything about CAS latencies for LPDDR DIMMs.

edit: to clarify: when overclocking RAM, your two options are either increase voltage or increase timings, as if you want to sustain higher speeds, you need to either charge your capacitors faster, or wait more cycles for them to be charged.

[erik]

> What about LPDDR (low-power DDR) allows it to be faster? And, by faster, do you mean lower latency? higher clock rates -> higher throughput? This is unintuitive to me.

By faster I mean higher throughput at similar latency, achieved by higher clock rates. And it is indeed unintuitive as to how this can be done while using less power than standard DDR.

My understanding is that it's down to two major factors:

1. JEDEC has iterated on the LPDDR standards much more rapidly. DDR4 and LPDDR3 both hit the market in 2012. But then LPDDR3e, LPDDR4, LPDDR4x, and LPDDR5 were all introduced before DDR5 was.

2. LPDDR isn't available on DIMMs, it's soldered only.

So given that most laptops sold by companies like Dell and Lenovo use soldered ram anyway, and that Intel and AMD both support LPDDR, then why are PC laptops with faster RAM so rare? I have no idea, maybe it costs a bit more and the manufacturers don't think they can market it as a benefit?

[theevilsharpie]

> So given that most laptops sold by companies like Dell and Lenovo use soldered ram anyway, and that Intel and AMD both support LPDDR, then why are PC laptops with faster RAM so rare? I have no idea, maybe it costs a bit more and the manufacturers don't think they can market it as a benefit?

For consumers, the primary application that benefits from higher RAM bandwidth is real-time graphics rendering, and non-Apple PCs optimize for this by using discrete GPUs with their own onboard high-bandwidth memory.

[jeffbee]

I wouldn't take the statement at face value. Most laptops base on 11th-gen Core and later Intel CPUs use LPDDR4x, just like the M1. It's not rare at all. It is the reference design from Intel.