What is Unified Memory on your Mac and How Does It Function?

Understand the distinctions between Apple's unified memory and conventional RAM.

If you have contemplated purchasing a contemporary Mac recently, you may have encountered the term unified memory in lieu of RAM. What is its significance, and how does it vary from conventional RAM? Continue reading to discover.

What constitutes Unified Memory?

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Many individuals mistakenly perceive the Apple silicon chip as merely a CPU, however this characterization is not totally accurate. It is, in fact, a System-on-a-Chip (SoC), encompassing multiple components within a single package, including the CPU, GPU, Neural Engine, and more elements.

All these components necessitate a temporary data storage solution for operation, which is where Apple's unified memory is utilized. Unified memory comprises exceptionally rapid DRAM chips housed within a single package, resulting in reduced power consumption and enhanced performance.

The primary benefit the SoC derives from this is the ability to employ a unified reservoir of high-speed, low-latency memory that is easily accessed by all components. This obviates the necessity for data replication across disparate memory regions, a procedure that can be laborious and demands supplementary power.

What distinguishes Unified Memory from conventional RAM?

The CPU and GPU in a conventional system possess distinct architectures and rely on various types of RAM for data retrieval. A conventional system with a dedicated GPU comprises two varieties of RAM: system RAM and VRAM (video memory).

VRAM transmits data to the GPU, while system RAM transfers data to the CPU. The primary limitation of conventional RAM is its connection to the CPU via a motherboard socket, which is typically slower than RAM integrated into the System on Chip (SoC).

Conversely, Apple silicon use an identical substrate for the installation of both the RAM and the SoC. Despite the RAM not being included within the SoC in this architecture, Apple employs a silicon interposer to link the RAM to the SoC.

This configuration indicates that the RAM is situated in close proximity to the components requiring access. This resolves the previously discussed bottleneck, enhancing power efficiency and speed, while also ensuring compatibility with the GPU without any compromises.

Is Unified Memory Superior in Speed Compared to Conventional RAM?

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As previously elucidated, the GPU and CPU possess distinct memory pools in conventional configurations. Conversely, Apple permits the GPU, CPU, and Neural Engine to utilize a shared memory pool, so eliminating the necessity for data transfer between distinct memory systems, which enhances the overall efficiency of the system.

The disparities in memory design result in the unified memory system providing elevated data bandwidth to the SoC. The M2 Ultra delivers a bandwidth of 800GB/s, much surpassing that of discrete GPUs such as the AMD Radeon RX 7800 XT, which gives a bandwidth of 624GB/s.

Nonetheless, the M2 Ultra does not provide the most favorable metrics within its category. NVIDIA's GeForce RTX 4090 and AMD's Radeon RX 7900 XTX surpass the M2 Ultra in memory bandwidth, achieving 1008GB/s and 960GB/s, respectively, as well as overall performance.

This elevated bandwidth permits the CPU, GPU, and Neural Engine to access extensive data reservoirs in nanoseconds. Consequently, this implies that memory depletion may occur more rapidly during CPU and GPU-intensive applications, such as gaming, due to the shared RAM across the entire System on Chip (SoC).

What is the requisite amount of Unified Memory?

The primary drawback of Apple's architecture is that the memory is integrated into the SoC, preventing future RAM upgrades for your Mac. On the majority of Macs, Apple imposes an exorbitant fee of $200 for an additional 16GB of unified memory; therefore, it is essential to evaluate your current and future requirements meticulously.

I utilize an M1 MacBook Air with 8GB of unified memory, which suffices for ordinary usage, although it occasionally encounters difficulties. I will certainly configure my future Mac with a minimum of 16GB of unified memory. If you require additional assistance in making an informed selection, we offer a specialized information on the appropriate memory requirements for your Mac.

Although the initial expense of enhancing unified memory may appear substantial, it may be more prudent to absorb that cost. It is more economical than purchasing a completely new Mac simply because you have discovered that your existing setup is inadequate for your activities two or three years later.