Editing CompactFlash (section)

===Speed===
CompactFlash [[IDE bus|IDE]] (ATA) emulation speed is usually specified in "x" ratings, e.g. 8x, 20x, 133x. This is the same system used for [[CD-ROM]]s and indicates the maximum transfer rate in the form of a multiplier based on the original audio CD data transfer rate, which is 150&nbsp;kB/s.

: <math>R = {K \cdot 150}\ \text{kB/s}</math>

where ''R'' = transfer rate, ''K'' = speed rating. For example, 133x rating means transfer rate of: 133&nbsp;×&nbsp;150&nbsp;kB/s = 19,950&nbsp;kB/s ≈ 20&nbsp;MB/s.

These are manufacturer speed ratings. Actual transfer rate may be higher, or lower, than shown on the card<ref>{{cite web|url=http://photofocus.com/2009/06/30/long-term-test-udma-flash-memory-lexar-won/|title=Photofocus – Long-Term Test – UDMA Flash Memory – Lexar Won|website=photofocus.com|access-date=18 March 2018|archive-url=https://web.archive.org/web/20180318185208/https://photofocus.com/2009/06/30/long-term-test-udma-flash-memory-lexar-won/|archive-date=2018-03-18|url-status=dead}}</ref> depending on several factors. The speed rating quoted is almost always the read speed, while write speed is often slower.

====Solid state====
For reads, the onboard controller first powers up the memory chips from standby. Reads are usually in parallel, error correction is done on the data, then transferred through the interface 16 bits at a time. Error checking is required due to soft read errors. Writes require powerup from standby, wear leveling calculation, a block erase of the area to be written to, ECC calculation, write itself (an individual memory cell read takes around 100 ns, a write to the chip takes 1ms+ or 10,000 times longer).

Because the USB 2.0 interface is limited to 35&nbsp;MB/s and lacks bus mastering hardware, USB 2.0 implementation results in slower access.

Modern UDMA-7 CompactFlash Cards provide data rates up to 145&nbsp;MB/s<ref>{{cite web|url=http://pietrzyk.us/media-card-study/|title=UDMA-7/UHS-1 Media Card Study|date=16 August 2013|website=pietrzyk.us|access-date=18 March 2018|archive-url=https://web.archive.org/web/20170211080838/http://pietrzyk.us/media-card-study/|archive-date=11 February 2017|url-status=dead}}</ref> and require USB 3.0 data transfer rates.<ref>{{cite web|url=http://pietrzyk.us/usb-3-0-cf-card-reader-study/|title=USB 3.0 CF Card Reader Study|date=14 August 2013|website=pietrzyk.us|access-date=18 March 2018|archive-url=https://web.archive.org/web/20161229054617/http://pietrzyk.us/usb-3-0-cf-card-reader-study/|archive-date=29 December 2016|url-status=dead}}</ref>

A direct motherboard connection is often limited to 33&nbsp;MB/s because IDE to CF adapters lack high speed ATA (66&nbsp;MB/s plus) cable support. Power on from sleep/off takes longer than power up from standby.

====Magnetic media====
Many {{convert|1|in|mm|adj=on}} hard drives (often referred to by the trademarked name "[[Microdrive]]") typically spin at 3600 RPM, so rotational latency is a consideration, as is spin-up from standby or idle. Seagate's 8&nbsp;GB ST68022CF drive<ref>{{Cite web | url=http://www.seagate.com/ww/v/index.jsp?name=ST1.2-Series_8-GB_CompactFlash_ST68022CF&vgnextoid=5ddc44ab7cffd010VgnVCM100000dd04090aRCRD&locale=en-US#tTabContentSpecifications |title = Seagate – Benut al uw gegevens maximaal &#124; Seagate Nederland}}</ref> spins up fully within a few revolutions but current drawn can reach up to 350 milliamps and runs at 40-50 mA mean current. Its average seek time is 8 [[Millisecond|ms]] and can sustain 9&nbsp;MB/s read and write, and has an interface speed of 33&nbsp;MB/s. Hitachi's 4&nbsp;GB Microdrive is 12 ms seek, sustained 6&nbsp;MB/s.