Ever wondered why copying a file to an external hard drive feels slow while your SSD-based machine flies? The answer comes down to data transfer speeds – and understanding the numbers across storage and networking technology helps you make better hardware decisions.
Bits vs. Bytes
Before looking at the numbers, there’s one conversion to keep in mind:
1 byte = 8 bits
- Network speeds are almost always quoted in megabits per second (Mbps) or gigabits per second (Gbps)
- Storage speeds are typically quoted in megabytes per second (MB/s) or gigabytes per second (GB/s)
So a 1 Gbps network connection has a maximum throughput of 125 MB/s (1,000 / 8 = 125). This distinction matters when comparing specs across different product categories.
Speed Comparison: Slowest to Fastest
| Technology | Mbps | MB/s |
|---|---|---|
| 100 Mbps Ethernet | 100 | 12.5 |
| SATA HDD | 800 – 2,000 | 100 – 250 |
| 1 Gbps Ethernet | 1,000 | 125 |
| 2.5 Gbps Ethernet | 2,500 | 312.5 |
| SATA SSD | 4,000 – 4,800 | 500 – 600 |
| 10 Gbps Ethernet | 10,000 | 1,250 |
| PCIe Gen3 NVMe SSD | up to 28,000 | up to 3,500 |
| 25 Gbps Ethernet | 25,000 | 3,125 |
| PCIe Gen4 NVMe SSD | up to 56,000 | up to 7,000 |
| 100 Gbps Ethernet | 100,000 | 12,500 |
| PCIe Gen5 NVMe SSD | up to 112,000 | up to 14,000 |
Storage: HDD to NVMe
Mechanical Hard Drives (HDDs)
HDDs use spinning magnetic platters to read and write data. The mechanical parts impose a hard ceiling on performance. Their main advantage is low cost per gigabyte, making them practical for mass storage where speed is secondary.
Typical sequential read/write: 100–250 MB/s
Performance varies based on RPM, data location on the platter (outer tracks are faster), and whether the access pattern is sequential or random. A modern 7200 RPM drive regularly hits 180–250 MB/s on sequential reads — fast enough that 1 Gbps Ethernet at 125 MB/s is frequently the bottleneck, not the drive itself. Random I/O on an HDD is dramatically slower than sequential.
SATA SSDs
SATA SSDs use flash memory instead of moving parts, which eliminates the mechanical bottleneck and dramatically improves both sequential and random I/O. They use the same physical interface as HDDs, and that interface (SATA III) caps their maximum throughput.
Typical sequential read/write: ~500–600 MB/s (near the SATA III theoretical limit)
NVMe SSDs
NVMe drives connect via the PCIe bus, bypassing SATA entirely and delivering a direct high-bandwidth path to the CPU. Performance scales with the PCIe generation:
| NVMe Generation | Typical Sequential Read |
|---|---|
| PCIe Gen3 | ~3,500 MB/s |
| PCIe Gen4 | ~7,000 MB/s |
| PCIe Gen5 | ~14,000 MB/s |
NVMe drives offer the largest single-component performance jump available in a modern consumer PC – noticeably faster boot times, application loads, and file transfers compared to any SATA drive.
Network Speed Tiers
| Standard | Theoretical Max |
|---|---|
| 100 Mbps Ethernet | ~12.5 MB/s |
| 1 Gbps Ethernet | ~125 MB/s |
| 2.5 Gbps Ethernet | ~312.5 MB/s |
| 10 Gbps Ethernet | ~1,250 MB/s |
| 25 Gbps Ethernet | ~3,125 MB/s |
| 100 Gbps Ethernet | ~12,500 MB/s |
Note that these are theoretical maximums. Real-world throughput is affected by network congestion, cable quality, switch and NIC capabilities, and the speed of the remote device you’re communicating with.
- 100 Mbps — legacy standard, rarely seen in new equipment
- 1 Gbps — the current baseline for home and small office networks
- 2.5 Gbps — increasingly common on mid-range motherboards and home routers; a meaningful upgrade without the cost of 10GbE infrastructure
- 10 Gbps — found in higher-end home setups and prosumer routers; starts to saturate fast NAS drives
- 25 Gbps and 100 Gbps — enterprise and data center territory
Practical Takeaways
- Upgrading storage: An NVMe SSD is the fastest single upgrade you can make to a PC. Even a Gen3 NVMe is 5–7x faster than a SATA SSD for sequential workloads.
- Building a home network: If you regularly transfer large files between machines, 2.5GbE is a low-cost bump; 10GbE unlocks the full speed of fast NAS drives.
- Internet service: ISP speeds are quoted in Mbps – divide by 8 for the MB/s you’ll actually see in your download manager.
- External storage: For backup or media use, an external SSD over USB 3.2 Gen 2 (10Gbps) far outpaces a spinning external HDD.