A speed label becomes useful when you know what it measures. Identify the Lexar CompactFlash model and its dated datasheet, then separate camera writing, video recording and computer offload. Each task has a different limiting component and a different useful measurement.
Decode the number and its direction
Lexar’s April 2018 Professional 1066x CompactFlash product sheet (PDF) defines 1x as 150 KB/s and labels 1066x as a read-transfer claim of up to 160 MB/s. In decimal units, 1066 × 0.15 MB/s = 159.9 MB/s, rounded to about 160 MB/s. Its footnote explicitly says writing is slower and actual results vary.
For an older card marked 12x, the same numerical scale would give 1.8 MB/s. That arithmetic alone leaves the original claim’s direction, test method and conditions unresolved. Find the document for that generation before treating a label as a writing specification.
Preserve a photo of the label and record the capacity, product line and part number. Apply the 2018 example only to the family it describes; use your camera’s support information to establish a usable match.
Match the rating to the task
On a narrow screen, swipe the table or focus it and use the arrow keys.
| Task | Useful evidence | What to observe |
|---|---|---|
| Still-photo bursts | Camera instructions plus card-writing performance in that camera | How many required frames are captured and how long the camera stays busy afterward |
| Continuous video | Required media for the exact recording mode and a sustained-write rating | Whether the full intended recording completes and plays correctly |
| Offload to a computer | Card read performance, matching reader, host connection and destination | Elapsed time for a defined file set, plus verification time |
The 2018 1066x sheet specifies VPG-65: a 65 MB/s minimum guaranteed video-write rate for compatible hosts and media. It also calls for a UDMA 7-enabled reader for its high-speed offload claim. Check both ends of the task; a card’s peak read number is insufficient evidence for a camera’s recording requirement.
Estimate an offload time with explicit assumptions
Use transferred data divided by the measured effective copying rate. Keep decimal units consistent: 12 GB = 12,000 MB. In a hypothetical workflow that sustains 80 MB/s, the transfer alone takes 12,000 ÷ 80 = 150 seconds, or 2 minutes 30 seconds. At 40 MB/s it takes 300 seconds, or 5 minutes.
These are invented rates, not benchmarks of a Lexar product. Setup, many small files, verification and interruptions can add time. If your deadline includes checking the copy, time that phase separately and add it to the transfer time. For example, a 150-second copy plus a measured 90-second verification totals 240 seconds: four minutes.
Run a useful comparison
- Use healthy media and preserve needed files first. Write down card identity, camera/firmware, reader, cable or adapter, port, computer and destination.
- For offload, use the same defined file set and destination conditions. Record bytes transferred, elapsed time and any errors. Calculate MB/s as bytes ÷ 1,000,000 ÷ seconds.
- Change one component when comparing results. State whether you measured an ordinary file copy or a benchmark; cached repeats and different file sets can produce incomparable numbers.
- For camera bursts, keep the shooting settings and subject conditions comparable, including file format and burst length. Observe the camera’s busy indication according to its manual. Treat the result as a camera-and-card result.
- Verify copied files and open representative content. Keep errors in the record; a fast incomplete copy fails the task.
Use the card offload record for repeatable notes. If results are slower than expected, investigate the connection and destination as well as the card. Choose a replacement only after the limiting stage is clear.