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Pretec P240 USB3 Card Reader

If you've bought a high end notebook in the past year it probably had a USB 3.0 port or two, but there has been little to plug into it. Recently this has changed. Pretec announced the P240, the first USB 3.0 (aka Superspeed) card reader on June 1, 2010, supposedly for mass production starting in August 2010. After a long delay the card started shipping in February of 2011. Was it worth the wait? That depends on your system and the type of flash cards you have. You will need a fast compact flash card and a fast hard drive to take full advantage of the P240 reader To understand this better, let's look at some transfer rates in megabytes per second (1 megabyte = 1,000,000 bytes)

Some theoretical transfer Rates:

The speeds above apply to both read and write operations. In practice read speeds are often higher than write speeds. For example, a Transcend 400x 64GB card is rated 60 MB/sec write, and 90 MB/sec read. Only the read speeds are important to photographers since we are usually copying images from a CF or SD card to a laptop's hard drive. You can see from the table that the interface is rarely the limiting factor in transfer speeds; even USB2 can theoretically read CF cards rated up to about 400x at full speed. Practice can vary widely from theory however. Finally, the table does not include any hard disks since drive read and write speeds depend strongly on the rotation speed and the number and density of the platters.

Testing the Pretec P240

How does the P240 perform in the real word when transferring images from your camera to your system? I tested on two PCs:

• A desktop with 24GB of memory, an Intel core i7 980X hex core CPU (3.33 Ghz) and a pair of Intel X25M - G2 drives running in a Raid 0 configuration, Win 7 64 bit was the operating system. USB 3.0 support was provided by an Asus U3S6 PCI-express card.
• A laptop (Hp Envy 15) with 16GB of memory, an Intel Q820 Core i7 processor (1.73 Ghz), and a Toshiba 1.8 inch 5400 RPM 250GB internal drive. Win 7 64 bit. The Envy 15 has two USB 3.0 ports. An external 160GB Intel X25M - G2 hard drive was also used for testing.

Three readers were tested:

• Pretec P240
• Sandisk Imagemate All in One - This is considered one of the fastest USB 2.0 CF readers. It was one of the readers tested in Rob Galbraith's review of CF reader performance which provides an independent check of USB 2.0 performance.
• Sandisk Extreme 3 (Old version) Reader - This is an old card and does not support UDMA transfers. It was also tested in Rob's review.

Two CF Cards:

• Transcend 64GB 400X. This card has a 400X write speed (60 MB/sec write, 90MB/sec max read)
• Transcend 32GB 133X. Transcend quotes rates of 15-40MB/sec. Oddly 15MB/sec is below the 133x spec of the card. Conversely I was able to achieve read speeds greater than the rated 40MB/sec max speed.

I didn't test any CF cards rated below 133x because the theoretical speeds are well below the rated speeds of even a USB2 reader. If you are using a card slower than 133x the brand of the USB2 reader will probably be the limiting factor. I only briefly looked at SD/SDXC cards; a Sandisk Ultra 64GB class 4 card appears in the disk benchmarks below. For SDXC, read speeds using the P240 were about 10 percent faster than those using USB2. The fastest SD cards are much slower than the fastest CF cards, see Rob Galbraith's SD benchmarks. SD speed rather than the interface is likely to be the limiting factor when transferring from an SD card.

Before running some actual card to computer transfers I took a look at sequential read and write speeds using the hard drive testing program Crystal Disk Mark 64 bit 3.0.1.2.

Read speeds approach 100MB/sec with the fastest CF card shown. To keep up with the card you need both a fast storage device and a fast reader.

Finally, I did some actual file transfers. 402 files totaling 9.345,224,425 bytes were transferred from card to computer. Average file size was about 23 MB, pretty typical of a RAW file on a 17-21 MP camera. Write caching was enabled so that it would be less likely that the speed of the hard drive being written to would limit transfer speeds. Here are the results:

The P240 is from 15% to 141% faster than a "good" USB2 reader, and from 103% to 324% faster than an old reader which does not support UDMA transfers. Desktop and laptop transfer times were generally comparable, so PC speed is not an important factor in transfer rate. The table makes it clear that the speed of the card is very important. The P240's gains with a slow card range from 32% to 39%, with a fast card from 15% (slow output device) to 141%. The output device can also limit the P240s transfer rates. Writing to the laptop's internal drive gives a transfer rate of 37.62 MB/sec, versus 81.76 MB/sec to an external SSD.

To see the best gains you need both a fast card and a fast output device.

Other thoughts / Conclusion

The P240 reads CF Type I and II, SD, SDHC, SSDXC. micro SD, micro SHDC, mini SD, mini SDHC, Memory Stick, Memory Stick Duo, Memory Stick Pro, and MMC. It is compact, about 2.6" x 1.4" x .7" in size. It is a "shallow" reader, meaning that the CF card doesn't go very deep in the reader/ Some say this increases the chance of bent pins. I had no problems however, and appreciated the small size.

The package contains a USB A Male to micro USB B dongle. The dongle stores in the reader when not in use, a nice feature for travel. Note that the package does not include a USB A M to micro USB B male cable. This can be a problem for some desktops and laptops. Most desktops still have their USB 3 port on the back on the PC, which means a cable will be needed to bring the port to the front. I have a USB 3.0 extension cable (A Male to A Female) that runs from the back of my PC to the front. In this way any USB3 device can be easily plugged in. Alternatively you could run a USB 3.0 A Male to micro USB 3.0 B cable from the rear to the front, and plug the P240 directly into it. Using this option to bring the USB 3 port to the front limits you to using USB3 devices that connect via micro USB. When using the dongle with my laptop I found that the dongle/reader combination interfered with some of the other attached devices. For example, I could not plug an HDMI cable into the laptop at the same time as the card reader. If you are going to use the P240 with a laptop you may want to purchase a USB 3.0 A Male to micro USB 3.0 B cable.

I purchased the card from mydigitaldiscount for $22.99 plus shipping. I have no relationship with this company.

I have now been to Kenya twice and typically shoot 20-30GB (1000-1500) images a day. When I get back to camp, where I have both limited power and limited time, the last thing I want to do is wait for my CF card reader to copy files to the laptop. If you've got a fast CF card, and a fast hard drive or SSD, you can cut transfer times by as much as 70% using the P240. With a slower card or hard drive you should also see some gains, but not nearly as much.

This page was last updated 3/23/2011