AWS r3.4xlargevsAWS r5a.4xlarge

r3.4xlarge pairs 16 vCPUs with 122GB of RAM at $1.3300/hr On-Demand (about $958/mo at 24×7). r5a.4xlarge pairs 16 vCPUs with 128GB at $0.9040/hr (~$651/mo). r5a.4xlarge is 32% cheaper per hour than r3.4xlarge ($0.4260/hr gap).

These are different generations of the same series. **r5a.4xlarge** is the newer generation, and AWS's pattern across generations is fairly consistent: ~10–15% better single-thread, 15–30% better multi-core, and similar or modestly higher per-hour pricing — so the price/performance per dollar usually improves with each generation. **r3.4xlarge** is still available and still works (AWS doesn't retire instance types quickly), but for new workloads the newer generation is typically the better default unless you have a specific reason to pin to the older AMI or there's a meaningful regional pricing advantage today.

On raw price-per-performance, the two are r5a.4xlarge delivers ~71% more single-thread Sysbench score per dollar (816 vs 1399 points per $1/hr). That's the cleanest signal we have for "which one runs your workload faster per dollar," but it only matters if your workload is single-thread-bound; for parallel workloads the multi-core scores (13410 vs 10501) are what to weigh. Spot pricing flips many of these comparisons — when r3.4xlarge drops to $0.3415/hr and r5a.4xlarge drops to $0.3402/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick r3.4xlarge when your workload is closer to memory-optimized (memory-bound work — in-memory databases, real-time analytics, large caches). Pick r5a.4xlarge when it's closer to memory-optimized (memory-bound work — in-memory databases, real-time analytics, large caches). When neither side is obviously right, the cheaper hourly rate usually wins for fault-tolerant batch workloads, while the higher single-core score usually wins for latency-sensitive web traffic. The regional pricing tables linked from each instance page below show where each is currently cheapest — sometimes a >20% regional gap flips the comparison entirely.