ARM processors are very popular in mobile devices and embedded systems. However, they do have some disadvantages compared to x86 processors typically used in PCs and servers.
While ARM processors are quite energy-efficient, their performance still lags behind high-end x86 processors. Some key factors related to ARM’s lower performance include:
- Lower clock speeds – Most ARM CPUs run at 1-2 GHz, while x86 CPUs can run at over 4 GHz.
- In-order execution – ARM cores execute instructions in program order, unlike x86 superscalar cores with out-of-order execution.
- Smaller caches – Cache sizes are smaller, resulting in more cache misses.
- Simpler branch prediction – Less sophisticated branch prediction hurts performance.
These architectural differences allow x86 chips to execute many more instructions per clock cycle. Highly parallel workloads like media encoding/decoding run much faster on x86 CPUs.
Lack of Compatibility
ARM and x86 have completely different instruction set architectures. An x86 CPU cannot execute ARM machine code, and vice versa. This means:
- Existing x86 software must be recompiled for ARM.
- Emulators are required to run x86 apps on ARM.
- Porting software between the architectures requires significant effort.
The lack of backward compatibility hurts ARM when trying to enter markets dominated by x86, like laptops and servers. Emulation and translation layers introduce performance overhead.
No High-Performance Server Chips
ARM processors are designed for power efficiency, at the cost of lower performance. Current ARM server chips like Amazon’s Graviton2 can compete with low-end x86 chips but cannot match high-end Xeon or EPYC processors.
ARM chips lack features critical for servers, like:
- Support for high core counts – Maximum cores are much lower than server-class x86 chips.
- Limited memory support – ARM chips support much less DRAM capacity and bandwidth.
- Minimal hardware virtualization support – Not suitable for virtualized environments.
- I/O limitations – Does not provide high-bandwidth I/O needed for storage/networking.
This makes ARM less attractive for large-scale cloud/enterprise servers requiring maximum performance.
Unlike the PC ecosystem dominated by x86, ARM has multiple vendors designing custom cores and architectures. This leads to fragmentation issues:
- Varying core designs – e.g. Cortex-A76, Apple A14, Qualcomm Kryo etc. make standardization difficult.
- Inconsistent architectures – Custom interconnects, memory support etc. varies across vendors.
- No unified instruction set – ARMv8-A has optional extensions, hurting compatibility.
- Software support headaches – OS/software support lags behind x86 due to the fragmented nature.
These differences make developing software and ecosystem tools for ARM very challenging compared to the unified x86 platform.
Research has shown certain security weaknesses in ARM processors that are not present in x86:
- Speculative execution flaws – ARM’s speculative execution makes it vulnerable to Spectre-type attacks.
- TrustZone flaws – Hacks like TrustZone Proxy can manipulate TZ to access secure data.
- No architectural side-channel protections – Unlike recent x86 chips supporting Mutex Decoy, Branch Predictor Sealing etc.
ARM TrustZone is also not as mature and proven as Intel SGX for trusted execution environments. More research/development may be needed to harden ARM against side-channel and speculative execution attacks.
Most companies licensing ARM cores are fabless semiconductor companies. As a result, ARM-based designs depend on third-party foundries like TSMC, Samsung, GlobalFoundries etc. This creates potential supply chain risks:
- Foundry capacity limits – Massive demand can create shortages for leading-edge fabrication.
- Geopolitical disputes – Trade wars and export controls can disrupt the foundry supply chain.
- Fabrication delays – Production delays at foundries quickly impact ARM chip supplies.
- Process technology lags – Foundries behind Intel in leading-edge lithography transitions.
In contrast, Intel controls its own cutting-edge fabs, giving it greater autonomy over x86 chip production. The external foundry reliance limits control over ARM processor supplies.
Licensing Cost Overheads
ARM processor cores and architectures require licensing from Arm Holdings. These IP licensing costs lead to increased overhead:
- Upfront costs – High fees to license ARM architectures and processor cores.
- Royalty payments – Ongoing royalty percentage paid per chip manufactured.
- Tooling costs – Expensive development tools add to overhead.
- Maintenance costs – Costs of tracking license compliance, renewals etc.
In contrast, x86 architectures do not require any licensing fees. ARM’s IP-based business model adds recurring costs that can offset profit margins.
In summary, key disadvantages of ARM processors compared to x86 include lower performance, lack of compatibility, an fragmented ecosystem, security concerns, supply chain dependencies, and licensing overhead. While ARM excels in power-efficiency, these factors currently limit its competitiveness in areas like PCs, servers and other performance-demanding computing segments. However, ARM technologies continue to evolve rapidly to address many of these limitations in the future.