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ExpressCard FAQ for ExpressCard 34 and ExpressCard 54

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ExpressCard FAQ for ExpressCard 34 and ExpressCard 54


What is ExpressCard?

ExpressCard is PCMCIA's (subsumed by the USB-IF) portable, removable, expansion technology to replace PC Card and PC CardBus (sometimes mistakenly called PCMCIA Cards). ExpressCard holds several advantages over PC Card some of which are enumerated below.

Differences between ExpressCard and PC Card

ExpressCard features new interconnect technology
ExpressCard utilizes two interconnect technologies, the most important of which is PCI Express (PCIe). ExpressCards featuring PCIe 1X technology are capable of 2.5Gb/s per direction, giving an ExpressCard operating in full duplex mode an approximate throughput of 250MB/s x 2, or 500MB/s of throughput, nearly quadrupling the effective speed of 32-bit PC CardBus. ExpressCard alternatively utilizes USB 2.0 for lower speed and less complex applications, with a maximum throughput of 480mb/s.
ExpressCard allows for much more bandwidth
ExpressCards featuring PCIe 1X technology are capable of 2.5Gb/s per direction, allowing for realization of applications, especially host adapters, that underperformed or were impossible under PC CardBus. Examples of full throughput host adapters that bottlenecked CardBus, but don't tax ExpressCard at all are FireWire 800 (IEEE 1394.b) and Gigabit Ethernet (GbE). Additionally, ExpressCard will be able to handle the latest SATAe and other high end buses with relative ease.
ExpressCard has superior power saving and management
ExpressCard operates at lower voltages than PC Card with 1.5 and 3.3V baselines. This allows systems deploying ExpressCard technology to take full advantage of current low power utilization throughout.
ExpressCard is a serial rather than a parallel bus
ExpressCard follows the trend of PCI Express and SATA in transitioning from parallel buses to serial buses. Rather than a 68-pin parallel connection used in PC Card, ExpressCard utilizes a 26-pin beam on blade serial connection. ExpressCard's use of high performance PCIe and USB 2.0 serial connections already built on to host system reduces complexity and eliminates the problems with signal timing associated with parallel buses.
ExpressCard is simpler and cheaper to implement than PC Card
Because ExpressCard harnesses buses that already exist on a host system, it doesn't require a separate ASIC to integrate it to a host system. Unlike PC CardBus and PC Card in which a controller chip was necessary to bridge between the card slot and the underlying system bus, ExpressCard devices literarily plug into either the PCIe or USB 2.0 bus on the system, depending on the ExpressCard type employed. ExpressCard saves in both cost and complexity in this regard.

Is ExpressCard backward compatible with PCMCIA PC Cards?

Our ExpressCard 34 to PCMCIA PC CardBus 16/32-bit Read-Writer Express2PCC allows computers with ExpressCard slots to use either 16-bit legacy PC Cards or 32-bit PC cardbus Cards. Express2PCC works with host systems featuring native ExpressCard 34 or ExpressCard 54 slots, or an installed PCIe to ExpressCard adapter. If the host operating system supports the PCMCIA PC Card, it should also work in conjunction with the Express2PCC. Sonnet's Qio device provides support for Panasonic P2 PC Card Memory devices on both Mac OS X and Windows. The Qio is available with either ExpressCard, PCIe, or Thunderbolt connections to the host system.


Is PCMCIA PC Card forward compatible with ExpressCard?

For PCIe based ExpressCards — in a word, no. However, it is useful to explain why this is the case. 32-bit PC Card CardBus card don't provide enough bandwidth to emulate ExpressCard. Furthermore, ExpressCard cards are completely different from PC Cards in voltages, form factor, physical connectivity and bus technology.

USB Mode ExpressCard Only Devices

While the PCMCIA ExpressCard specification requires all host adapters and slots to support both PCIe and USB 2.0 portions of the ExpressCard bus, several products are now on the market that only support the USB 2.0 mode. While this technically breaks the specification, many consumers have been clamoring for such a device. In response to such demand, products are now appearing on the market that bridge between PCMCIA PC Card and USB 2.0 based ExpressCards. Several new devices behave like USB 2.0 hubs, routing an ExpressCard's USB 2.0 through a PCMCIA PC Card slot. PCMCIA PC Card to USB 2.0-Mode ExpressCard adapters are available as 32-bit and 16-bit PCMCIA PC Card varieties. PC Card USB 2.0 mode ExpressCard host adapters cannot work with any PCIe based ExpressCards. This is true for USB to USB 2.0-Mode ExpressCard adapters like our MicroU2E series as well.

ExpressCard Dimensions

ExpressCard Dimensions Diagram

ExpressCards come in two form factors: ExpressCard 34 and ExpressCard 54. The form factors share the same dimensions except for width, from which the names of the form factors are derived. ExpressCard share a length of 75mm and a depth (or thickness) of 5.0mm — the same depth as Type II PC Cards. Both the widths and shapes of the two ExpressCard form factors are different, but the portion of the card which connects to the card slot are an identical 34mm. ExpressCard 34 cards are 34mm wide and rectangular in shape. ExpressCard 54 Cards are 54mm wide at their widest point and 34mm wide at the connection point, creating a shape often referred to as a "Fat-L". Either form factor is allowed additional volume extending outside of what would be considered the flush portion of an inserted card. This is referred to as the extended portion of the card and ExpressCards with such a configuration are referred to as extended cards. The extended portion can exceed the card dimension in any axis, but there are obvious practical limitations to how much. For an excellent example of an ExpressCard with an extended portion on two axis (depth and width) see: ExpressCard 34 to CompactFlash Memory Card Adapter. For an explanation of how ExpressCard modules are used in the two types of ExpressCard slots, please see ExpressCard Slotting.

ExpressCard Slotting

ExpressCard Slotting Diagram

ExpressCard slots come in two varieties; those designed for both ExpressCard 54 and 34 cards, and those for ExpressCard 34 cards only. ExpressCard slots are required to provide both PCIe and USB 2.0 functionality, regardless of their size. ExpressCard 54 slots, as pictured in figures A and B on the right, are able to accept both 54 and 34 cards. What PCMCIA describes as a "novel guidance device," which seen in the lower left corner of figures A and B, physically guides an ExpressCard 34 device to the connector part of the slot. Since the connection part of the card for both types of ExpressCards is identically 34mm, this scheme provides an elegant solution for utilizing both types of cards. Conversely, only ExpressCard 34 cards fit in ExpressCard 34 slots as pictured in figure C. Paying attention to this last fact is important when shopping for ExpressCard products, if a device only has an ExpressCard 34 slot, then only shop for ExpressCard 34 devices.

PCMCIA literature has expressed that systems deploying multiple ExpressCard slots should lay them out adjacently on a horizontal plane rather than the "stacked slot" convention employed by PC Card slots.

Is there a way to stabilize ExpressCard/34 inside ExpressCard/54 slots?

Synchrotech SlotGuardExpress ExpressCard/34 Stabilizer Insert for ExpressCard/54 Slots

While it may have seemed a sound idea to engineers designing the original ExpressCard standard, one of the more perplexing — and troublesome — aspects of the design has been using ExpressCard/34 cards in ExpressCard/54 slots. In practice, ExpressCard/34 cards, even when properly seated, aren't stable when inserted in the larger ExpressCard slots. The gap between the card and the larger slots allowed cards to be easily dislodged or come loose. This problem is more evident when ExpressCards with large "extended card" portions, and/or with cables attached to them. When cards come loose and disconnect during operation, they drop signal, or worse, can damage the ExpressCard and even the ExpressCard slot. This is especially true for cards providing electrical current, like many Serial I/O ExpressCards.

The SlotGuardExpress ExpressCard/34 Stabilizer Insert for ExpressCard/54 Slots protects against ExpressCards being dislodged from their slots. SlotGuardExpress is an inexpensive, non-conductive insert that attaches to the side of an ExpressCard/34 to eliminate the free-play between the card and the ExpressCard slot. SlotGuardExpress is available as a product for individual end users and for Original Equipment Manufacturers (OEM who want to include it with their ExpressCard/34 products. SlotGuardExpress puts an end to disrupted connections and equipment damage caused by ExpressCards moving side to side (laterally) in larger slots.






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