How long to download 100 GB at 500 Mbps

One thousand six hundred seconds, read from the disk side

One hundred gigabytes is 800,000 megabits. A 500 Mbps line carries 500 megabits a second, so the transfer needs 800,000 divided by 500, which is 1,600 seconds, or 26 minutes 40 seconds. That much is one sum. The awkward part starts when the same number is read from the other end of the connector: during those 1,600 seconds the machine has to accept 62.5 megabytes every second, without a pause, for half an hour.

The prefix is where the sums start. A gigabyte is 10⁹ bytes under the base ten reading the NIST prefix table sets out, so 100 GB is 100,000,000,000 bytes and 800,000,000,000 bits. Convert once and the rest follows. Five hundred megabits a second is 62.5 MB/s, an hour moves 225 GB, and each gigabyte costs 16 seconds. At this rate a large download stops being a network event and becomes a storage event, because the line is no longer the slowest thing in the chain by a wide margin.

The drive has to accept 62.5 MB/s for 27 minutes

Downloads stream to disk, so the finish time is the larger of two numbers: the line clock and the time the storage can absorb the payload. At 500 Mbps the second number stops being trivially small. One hundred gigabytes is 100,000 megabytes, and dividing that by a sustained write rate gives the minimum the disk sets.

Work two cases. A shingled 2.5 inch drive that sustains 40 MB/s after its cache empties needs 100,000 divided by 40, which is 2,500 seconds, or 41 minutes 40 seconds. The line finishes its half in 1,600 seconds and then waits 900 seconds for the platters. A USB 2.0 flash stick at 30 MB/s is worse: 3,333 seconds, or 55 minutes 33 seconds, and the transfer spends two thirds of its life blocked on the controller.

The crossover sits at 62.5 MB/s, and it is worth knowing where a given device falls. A card that advertises UHS-I has a bus ceiling of 104 MB/s and typically writes at 60 to 90, so it clears the bar by a small margin. A spinning drive clears it on the outer tracks and misses it on the inner ones, which is why a large file copied to an old external drive starts fast and ends slow.

A write test is the only way to know which case applies. Copy a 10 GB file to the target with a tool that bypasses the page cache, then read the rate at the end rather than the first five seconds. The opening burst comes from SLC cache or from DRAM, and it can be three times the sustained figure. A disk that holds 400 MB/s for ten seconds and then settles at 90 is a 90 MB/s drive for this purpose, because 1,600 seconds is far longer than any cache.

PCIe lanes, queue depth and the 29 second write

A modern NVMe drive is not close to being a limit. PCIe 3.0 moves 8 gigatransfers a second per lane, encodes them at 128/130, and four lanes therefore carry about 3.94 GB/s. PCIe 4.0 doubles the transfer rate and reaches roughly 7.88 GB/s over the same four lanes. A drive rated at 3,500 MB/s writes 100 GB in 28.6 seconds, which is 1.8 percent of the 1,600 second download.

The number that matters is not the peak, it is the shape of the workload. One hundred gigabytes of large files is a sequential stream and any NVMe drive handles it. One hundred gigabytes of 4 KB files is 25 million separate operations, and a desktop file system that creates 20,000 of them a second spends 1,250 seconds, or 20 minutes 50 seconds, just on metadata before the payload is counted. A download that unpacks an archive into thousands of small files behaves like the second case, not the first.

Steam, the Steam Deck and the install phase nobody counts

Game launchers are the most usual place people meet a 500 Mbps line, and they are also where the clock is least honest. Valve lists the Steam Deck with a 512 GB or 1 TB NVMe SSD, a microSD slot rated UHS-I, and a tri-band Wi-Fi 6E radio with 2x2 MIMO, all on the Steam Deck specification page. A 500 Mbps plan asks for 62.5 MB/s, a fraction of what that radio and that SSD handle together, so the hardware is not the ceiling in the good outcome.

Steam splits a download into two phases. The first pulls compressed depot data, and the second unpacks and patches it on disk. Only the first phase uses the network. If the download runs at the full 500 Mbps for 1,600 seconds and the install phase then unpacks 100 GB at 400 MB/s, that phase costs 250 seconds, and the job ends at 1,850 seconds, or 30 minutes 50 seconds. The status bar shows 100 percent for four of those minutes while the network sits idle, which is exactly when people start testing their connection.

The microSD case is the one to watch on a handheld. UHS-I tops out at 104 MB/s on the bus and lands nearer 60 to 90 in practice, so it sits just above the line and any dip puts the card in charge. A card that writes at 30 MB/s turns the same install into 3,333 seconds, 55 minutes 33 seconds, and the Wi-Fi is blamed for all of it.

Wi-Fi 6E at 2x2 on a 160 MHz carrier carries several times the 500 Mbps the plan delivers, so a handheld in the same room is fine. A 2.4 GHz fallback is not. The radio has to clear 62.5 MB/s of payload before the plan matters at all.

A single stream needs a 2.5 MB window at 40 ms

A TCP sender may have one receive window of data in flight, so the rate it can sustain is the window divided by the round trip. Turn that around and a 500 Mbps path needs a window of 62.5 MB/s multiplied by the round trip: 1.25 MB at 20 ms, 2.5 MB at 40 ms, and 5 MB at 80 ms. Those are large windows, and they only exist when both ends negotiate window scaling.

An old host, an embedded app or a proxy that stops at 64 KiB caps one socket at 65,536 bytes per round trip. At 20 ms that is 26.2 Mbps, and the file then needs 30,518 seconds, or 8 hours 28 minutes 38 seconds, on a circuit that tests at 500. At 80 ms the same stream drops to 6.6 Mbps and the job runs for 33 hours 54 minutes.

Parallel connections are the usual workaround. Eight streams at 40 ms carry 104.8 Mbps, which is 7,629 seconds, or 2 hours 7 minutes 9 seconds, and still well under the line. Nineteen streams come within 1 percent of 500 Mbps at 20 ms, and thirty eight do the same at 40 ms, which is why a download manager with eight connections helps a distant server and does nothing for a local one.

The cap, the upload half and the tier above

At 225 GB an hour, a 100 GB file is 10 percent of a 1 TB monthly allowance and the whole allowance lasts 4 hours 26 minutes 40 seconds of continuous transfer. That is the point where a 500 Mbps plan stops feeling unlimited, and it is why caps and speed tiers are usually discussed together.

The sending direction is the asymmetry to check before buying. The FCC set a long term goal of 1 Gbps down and 500 Mbps up in the 2024 order numbered FCC 24-27, adopted March 14, 2024, which replaced the 25/3 yardstick with 100/20. A plan sold as 500 Mbps down is frequently 500 down and 20 up, and the same 100 GB archive then takes 40,000 seconds to send, or 11 hours 6 minutes 40 seconds. A symmetric 500 Mbps fibre plan takes 1,600 seconds each way.

One tier up, at 1 Gbps, the same file lands in 800 seconds, 13 minutes 20 seconds, and the disk budget doubles to 125 MB/s. That is the point where a SATA SSD stops being comfortable and an NVMe drive becomes the sane target. At 2.5 Gbps the clock is 320 seconds, 5 minutes 20 seconds, and the storage requirement passes what most consumer drives sustain once their cache is exhausted.

Tests before a 27 minute transfer

Three measurements catch almost every problem on this tier, and all three take less time than the download. Write 10 GB to the target drive with a sequential tool and watch the rate at the end rather than the start. Run iperf3 with four streams. Read the negotiated link speed on the network adapter. A 100 Mbps port turns the job into 8,000 seconds no matter what the plan says, and a 1 Gbps port is enough at 940 Mbps of payload.

Eighteen and three quarter gigabytes in five minutes is the full-rate signature, since 62.5 MB/s multiplied by 300 seconds is 18,750 MB. Anything less than 15 GB means the path is delivering under 400 Mbps, and the counter tells you which stage to suspect: a rate that starts at 500 and decays points at the drive cache, while a rate that never reaches 400 points at the network.