What is unified memory?

If you’ve bought a Mac recently, or are considering buying one, you may have noticed that Apple sells computers with what’s called ‘unified memory’ instead of the traditional random access memory (RAM). What is unified memory, you might be wondering, and is it better or worse than good old RAM? Let us explain.

Related reading: MacBook Air 15 vs MacBook Air 13: Which is better for business?

How unified memory works

Unified memory is found on systems that use Apple’s own processors, the first iteration of which is called M1. Now, instead of the insides of your computer being lots of separate components (an Intel processor, an Nvidia graphics chip, say) that are attached to a motherboard, the latest Apple Macs are what’s known as a system-on-a-chip (SoC), where the processor, the graphics chip and the memory are all part of the same package.

In the past, the graphics chips – the component that is predominantly used to power games – would have come with its own physical allocation of memory. This was separate from the main system memory (or RAM).

Unified memory does away with those two discrete pools of memory and combines them into one, hence the name.

Related reading: Graphics workstations: CPU vs GPU

Is unified memory better?

Unified memory might sound like a backwards step, especially as Apple ships even its latest iMac with only 8GB of unified memory. This is a relatively paltry amount by today’s standards: the 2019 MacBook Pro I’m writing this article on, for instance, has 32GB of RAM and 4GB of memory devoted to the graphics chip. That’s almost five times as much RAM as the new M1-based MacBook Pro 13in.

However, the two aren’t directly comparable because unified memory is much more efficient.

Let’s use a game as an example. When I fire up a game on my MacBook Pro, the processor, system RAM, graphics chip and graphics memory must all work in sync for smooth frame rates. However, that involves bits of data being shuttled back and forth between components, which creates a bottleneck.

With unified memory, the main processor and the graphics processor have access to the same pool of memory, so there’s no need to shuttle data back and forth between the two. What’s more, each component has access to the full quota of memory. So, in the example above, once the 3D action in the game kicks off, the graphics chip can use the majority of the unified memory to work its magic. You might recall my old MacBook Pro had only 4GB of graphics memory, whereas the new MacBook Pro has up to 8GB to play with, which is likely to lead to better overall performance, even though it has less memory overall.

In fact, we’ve seen in benchmarks published in magazines such as PC Pro that even the cheapest MacBook Air (£999) based on the new M1 processors can keep pace with my 2019 MacBook, which cost more than £3,000. No, you’re crying.

Should I go for 8GB or 16GB?

Given everything I’ve said above, you may be wondering whether it’s even worth upgrading to 16GB of unified memory, which is an option offered on some Macs. My advice – as ever – is to go for the best spec your budget allows. Even with its improved efficiency, there will be times when you saturate the 8GB of unified memory when doing intensive tasks such as gaming, video editing or photo editing. Nobody ever got sacked for buying more memory!

That said, if you’re only planning to use a MacBook Air for web surfing, word processing and other basics, then the 8GB should do you just fine. You’d be better off investing in larger storage (SSD) if you have the budget to spare, especially on systems with only 256GB of storage.