What is the difference between Intel Xeon and AMD EPYC in EC2?

Amazon Elastic Compute Cloud offers both Intel Xeon Scalable and AMD EPYC processors to power its virtual machine instances across general-purpose, compute-optimized, and memory-optimized families. While both processor lines are built on the x86-64 instruction set architecture and share broad software compatibility, they differ in core architecture, hardware acceleration features, memory bandwidth, and pricing models. Intel Xeon instances emphasize single-thread clock speeds and specialized built-in accelerators for artificial intelligence and cryptography, whereas AMD EPYC instances focus on high core density and lower cost per virtual CPU.

Naming Conventions in Amazon EC2

Amazon EC2 identifies the underlying processor vendor through the instance family naming scheme. By default, standard x86 instance families without a processor suffix run on Intel Xeon Scalable processors. Instances powered by AMD EPYC processors append the letter a immediately after the instance family letter and generation number.

For example, in the seventh-generation general-purpose family:

• m7i and m7i-flex instances use 4th Generation Intel Xeon Scalable processors (Sapphire Rapids).
• m7a instances use 4th Generation AMD EPYC processors (Genoa).

Similarly, in the sixth-generation families, m6i, c6i, and r6i run on 3rd Generation Intel Xeon Scalable processors (Ice Lake), while m6a, c6a, and r6a run on 3rd Generation AMD EPYC processors (Milan).

Architectural and vCPU Differences

A key technical distinction in modern EC2 generations lies in how virtual CPUs (vCPUs) map to physical processor cores.

In Intel Xeon-based EC2 instances (such as M6i, C6i, M7i, and C7i), Simultaneous Multithreading (Intel Hyper-Threading Technology) is enabled by default. Each vCPU corresponds to a single hardware thread, meaning two vCPUs share one physical CPU core:

\[\text{Physical Cores}_{\text{Intel}} = \frac{\text{Total vCPUs}}{2}\]

In contrast, starting with 7th-generation AMD EPYC instances (M7a, C7a, and R7a), AWS disables Simultaneous Multithreading (SMT). Every vCPU in a 7th-generation AMD instance is a dedicated physical core rather than a shared thread:

\[\text{Physical Cores}_{\text{AMD (Gen 7)}} = \text{Total vCPUs}\]

Note that earlier 6th-generation and 5th-generation AMD instances (such as M6a and M5a) still map one vCPU to one SMT hardware thread, except for specific high-performance computing instances like hpc6a. Having a 1:1 mapping of vCPUs to physical cores in 7th-generation AMD instances eliminates thread contention on the same core and provides predictable scaling for compute-bound workloads.

Instruction Sets and Built-in Accelerators

Both processors support standard x86 vector extensions, including AVX, AVX2, and AVX-512 (supported across Intel Xeon Scalable generations and introduced to AMD EPYC starting with 4th Gen Genoa in M7a/C7a/R7a instances). However, Intel includes dedicated silicon accelerators on 4th Generation Xeon Scalable processors (M7i, C7i, R7i) that are not present on AMD EPYC processors:

• Intel Advanced Matrix Extensions (AMX): Accelerates matrix multiplication operations for deep learning training and inference workloads using BF16 and INT8 data types.
• Intel Data Streaming Accelerator (DSA): Offloads high-performance data movement and transformation tasks from the CPU cores.
• Intel In-Memory Analytics Accelerator (IAA): Improves the performance of analytics and database workloads by accelerating compression and decompression in memory.
• Intel QuickAssist Technology (QAT): Hardware acceleration for cryptography and data compression.

AMD EPYC processors counter with high L3 cache density and memory bandwidth, utilizing a chiplet-based architecture (Core Complex Dies connected via AMD Infinity Fabric) that scales up to 192 physical cores (48xlarge size) in 7th-generation EC2 instances, compared to a maximum of 192 vCPUs (96 physical cores) on standard 48xlarge Intel instances.

Pricing and Cost Efficiency

Across equivalent EC2 instance generations, pricing between Intel and AMD depends on whether the generation uses hyper-threaded vCPUs or dedicated physical cores:

• 5th and 6th Generation (m5a/m6a vs m5/m6i): AMD EPYC instances are priced approximately 10% lower than comparable Intel Xeon instances of the same vCPU count and memory allocation. For workloads that do not rely on Intel-specific instruction sets, m6a, c6a, and r6a serve as direct cost-saving drop-in replacements.
• 7th Generation (m7a vs m7i): Because every vCPU on an m7a, c7a, or r7a instance is a full physical core (with no SMT sharing) running at a higher base and boost frequency, 7th-generation AMD instances carry a higher per-vCPU hourly rate than m7i instances, but deliver higher raw compute performance per vCPU.

Comparison Summary

How to Choose Between Intel and AMD on EC2

Choose Intel Xeon Scalable (i instances) when:

1. Workloads use Intel-specific optimizations: Applications compiled with the Intel oneAPI Math Kernel Library (oneMKL), OpenVINO, or workloads leveraging Intel AMX for AI inference benefit directly from Intel hardware.
2. Per-vCPU software licensing is a factor on 7th Gen: If commercial software is licensed per vCPU and does not require a dedicated physical core per vCPU, m7i or r7i instances provide lower per-vCPU infrastructure costs than m7a or r7a.

Choose AMD EPYC (a instances) when:

1. Lowering baseline cloud spend (6th Gen): General web servers, microservices, containerized applications, and development environments running on m6a, c6a, or r6a gain up to 10% cost savings over m6i, c6i, and r6i with minimal performance difference.
2. Maximizing physical core count and avoiding noisy-neighbor threads (7th Gen): High-performance computing, electronic design automation (EDA), financial modeling, and video encoding workloads benefit from the 1:1 physical core mapping and up to 192 physical cores per instance in c7a, m7a, and r7a.