Unified memory
There’s a cost but unfied memory helps to make Apple silicon Macs more efficient
HOW IT WORKS
YOU WILL LEARN How unified memory works in comparison to Random Access Memory (RAM) etween 1997 and 2002, Apple used the advertising slogan “think different”. Fast forward to today and that long-running campaign is a distant memory yet the sentiment behind it is very much alive. You can see the difference when looking at how Apple has set modern Macs apart from ‘normal’ computers. Rather than have separate central and graphics processing units – CPU and GPU – and Random Access Memory (RAM) components, Apple silicon Macs make use of a System-on-a-Chip (SoC). And that move has made them very powerful indeed.
One of the big decisions rolled out in the creation of the cutting-edge proprietary M1 chip in 2020 was the introduction of unified memory. As well as integrating components such as the CPU, GPU, I/O controllers and Apple’s Neural Engine (the specialised cores used for the acceleration of AI and machine learning), the M1 chip is directly connected to memory via a layer of silicon. It speeds up the transfer of data and makes processing more efficient. But there’s a reason for the word ‘unified’.
To explain, RAM is temporary storage for files, allowing software somewhere to place and access data so that it’s more readily available for processing. RAM is volatile in the sense that it requires power – if you turn a computer off, the
BRAM content is lost – yet, by making use of RAM, computers run more quickly. RAM is faster than storage drives so data can be accessed much faster. But the way computers traditionally allocate memory is different in comparison to Apple silicon (which is now on its third gen).
Normal v unified
Normal computers have a separate CPU and GPU with memory also located separately. The two processors will then dip into different pools of memory. The CPU will access RAM or DRAM (Dynamic RAM that requires regular refreshing but is fast and reliable despite being more power-hungry) while the GPU will access VRAM (Video RAM) which the CPU can also use.
Since these two processors need to work together, however, there’s a lot of shuttling backwards and forwards using buses and the like. A bus is a connection that allows data to move between the processor and RAM but if you imagine that the CPU is making use of info stored in the RAM and sending data to the VRAM for the GPU to pick up, process, send back to the CPU to be processed and stored in the RAM, then you can see that it can get a little messy. Having the different processors work on the same data and pass it from one pool to another only serves to slow things down.
If your Apple silicon Mac is using up all of your unified memory, the computer will make use of swap memory. This borrows space from your Mac’s startup disk, allowing unused files to be swapped back and forth between the RAM and your solid-state drive (SSD). Ideally, this will be used sparingly because it can damage and shorten the life of your SSD.
Key fact