TechCompare LogoTechCompare

RAM disk vs NVMe SSD: when putting your data in RAM makes sense

A RAM disk turns system memory into a block device with roughly 80 ns latency and 100+ GB/s bandwidth, compared to an NVMe SSD's 100 µs latency and 7 GB/s bandwidth. For random access, a RAM disk is 1,000x faster. The trade-off: everything in a RAM disk disappears when the machine loses power or reboots.

Hardware tier
Storage
Persistent storage devices
Topic focus
RAM disk vs NVMe
ramdisk-vs-nvme

How this is calculated

RAM disks make sense for workloads where the data is either ephemeral (compile artifacts, temporary database tables, video rendering scratch space) or easily regenerated from persistent storage (caches, indexes). Linux's tmpfs creates a RAM-backed filesystem that can swap to disk under memory pressure. Windows has a built-in RAM disk via ImDisk or third-party tools. For databases, putting tempdb or a read replica entirely in RAM can dramatically improve query performance. Modern build systems (Bazel, Buck2) use RAM disks for compile caches by default. If your data can be lost without consequence and you need maximum random I/O, a RAM disk is the right tool.

Verdict

Use a RAM disk for ephemeral, performance-critical data that can be regenerated. Don't use it for anything you'd be upset to lose. For most workloads, the OS page cache already keeps frequently accessed files in RAM automatically, making an explicit RAM disk unnecessary.

More Latency scenarios

L1 vs L2 cache
l1-vs-l2
View details ➜
L3 cache vs RAM
l3-vs-ram
View details ➜
DDR4 vs DDR5 latency
ddr4-vs-ddr5
View details ➜
NVMe vs SATA SSD
nvme-vs-sata
View details ➜
SSD vs HDD speed
ssd-vs-hdd
View details ➜
CPU cache hierarchy
cache-hierarchy
View details ➜
Memory latency numbers
latency-numbers
View details ➜
Storage tier guide
storage-tiers
View details ➜
Optane vs NAND
optane-vs-nand
View details ➜
PCIe 4.0 vs 5.0 SSDs
pcie-gen4-vs-gen5
View details ➜

Frequently asked questions

How much faster is L1 cache than RAM?
Roughly 40-60x faster for random access. L1 cache access is about 1 ns; DDR5 RAM is about 50-80 ns end-to-end including controller overhead. That's why keeping hot data in cache dominates real-world CPU performance.
Is NVMe SSD faster than RAM?
No. NVMe is fast for storage, but for random access its latency is around 50-150 µs versus RAM's 50-80 ns. That's a 1,000x gap. NVMe beats RAM only on raw capacity and persistence, never on latency.
Why is HDD so much slower than SSD?
A spinning HDD has to physically move a read head to the right track and wait for the platter to rotate into position, typically 5-15 ms per random access. An SSD has no moving parts and returns data in under 100 µs, roughly 100x faster for random reads.
What's the point of L3 cache?
L1 and L2 are tiny (KB to low MB) and per-core. L3 is much larger (tens of MB) and shared across cores, acting as a buffer before requests go to main RAM. It catches data evicted from L1/L2 and data shared between cores.
How many nanoseconds is one CPU cycle?
At 4 GHz, one cycle is 0.25 ns. At 5 GHz, 0.2 ns. Cache hits are measured in single-digit cycles; main memory access costs hundreds of cycles, which is why optimizing for cache locality matters enormously in performance-critical code.
Does DDR5 have lower latency than DDR4?
Not usually at the same relative tier. DDR5 improved bandwidth and capacity significantly, but true latency (in ns) for mainstream kits is similar to late-stage DDR4. The gains from DDR5 come from bandwidth and larger capacities, not lower memory latency.

Related tools

RAM Latency Calculator

Convert DDR3/DDR4/DDR5 timings (CL, tRCD, tRP, tRAS) into true latency in nanoseconds.

Use tool ➜

RAID Calculator

Calculate usable capacity and fault tolerance for RAID 0, 1, 5, 6, and 10.

Use tool ➜

Display Bandwidth Calculator

Check if your HDMI/DP cable supports your resolution and refresh rate.

Use tool ➜