One of the most common details in laptop specifications is that in some models the type of RAM is mentioned as the LPDDR5which is usual for mobile phones and on paper, at least in transfer speed compares to DDR5. However, things are not as simple as they seem.
One of the advantages of the PC over consoles is not relying on a single pool of memory for graphics and general processing, which happens on mobile phones and video game consoles. The curious thing about LPDDR5 and GDDR6 is that they share one thing in common, they value bandwidth in exchange for sacrificing latency, which means the CPU performs worse.
Why is LPDDR5 worse than DDR5 on PC?
In theory and on paper, DDR5 and LPDDR5 memory have the same performance when looking at their bandwidth, but with a few small differences. Most clearly, there are no DIMM or SO-DIMM format memory modules that use LPDDR5 memory. This is why Intel and AMD desktop processor specifications do not support this type of RAM, as it is not used.
However, despite being called Low Power or low consumption, LPDDR5 has nothing to do with DDR5, nor is it a low-power version. They are two different JEDEC approved memory standards and therefore have different communication times between the two memory types and this is where the problem comes in. Have you ever wondered why LPDDR5 latencies are not public? Well, for the simple fact that they are much worse than DDR5 and end up being a bottleneck for the system CPU. In other words, when choosing a laptop, if it has DDR5 memory, it will have better CPU performance than LPDDR5, however, more and more models are being sold with this configuration, in especially ultra-thin laptops.
Why does it happen?
Contrary to what many people think, mobile chips have much lower CPU performance than PC chips, so lower latency doesn’t lead to as big of a performance hit. Let’s not forget that most laptops with LPDDR5 memory are used for very light tasks with very low clock speed CPU models in their daily use.
The assembler’s dilemma
LPDDR5 memory is designed to work in mobile devices and therefore they are very thin, many even with totally passive cooling and it is a plus in certain heat dissipation conditions to opt for said memory instead of DDR5 at the time of making ultra-thin laptops.
While it is true that DDR5 memory can be soldered onto the board, most memory chips sold come in DIMM and SO-DIMM modules, and individual chips tend to be more expensive. Besides the fact that they emit much more heat than LPDDR5 and that’s why they are discarded when building some laptops.
What is indeed a mistake is that in mainstream laptops, those that usually have a processor ending in H or HX in their name, and, therefore, have the ability to support DDR5 memory without issue and even GDDR6 graphics cards. Well, if you see a gaming laptop with these specs, then throw it out of the blue, its CPU performance will be capped by the bottleneck that assumes the use of memory with higher latency .
