Selecting a PCMCIA PC Card/PC CardBus Drive/Read-Writer, a Primer and FAQ
Introduction
Synchrotech's line of PCMCIA PC Card and PCMCIA Media readers is extensive. This introduction is intended to provide help in choosing the right reader. Selecting the right reader depends upon several factors including: the type of cards in use, the bus technology used to connect the reader to the host computer, and the form factor of both the card and the reader. Other considerations include single, dual or multiple slots, speed, cost and portability.
Choosing a Bus Technology to Support a PCMCIA PC Card
There are some important concerns when it comes to the host computer bus technology when selecting a reader. To simplify this, we shall divide PCMCIA PC Card technologies into the following categories:
- Legacy PCMCIA PC Card (16 bit)
- This is the original PCMCIA PC Card standard under which fall three categories:
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- ATA Mass Storage Cards Includes both ATA Flash and Rotating Hard Drives. Nearly all storage and consumer media types in their various form factors fall here. Examples of ATA Flash media include: ATA Flash, CompactFlash, SmartMedia, MultiMediaCard, Secure Digital MMC, and Memory Stick. Rotating Hard Drives types include Microdrives (1.0 inch CompactFlash Type II), and Toshiba's PC Card Hard Drives (1.8 inch PC Card Type II).
- Storage Cards This includes SRAM, Linear Flash, and Miniature Card. While this storage media differ little in end use functionality from ATA storage, their non-IDE driver requirements, and in the case of Linear Flash, specialized file systems make them difficult to support in comparison.
- I/O Cards This includes any card that provides IO to the host or requires interrupts. A sample list would consist of items like Modems, Ethernet, Serial, Video and Sound cards. These are essentially ISA/EISA card style devices except in the way they connect to the host computer.
- CardBus PCMCIA PC Card (32 bit)
- The CardBus specification was published by PCMCIA around 1996. While legacy IO PCMCIA PC Cards are modeled on ISA/EISA, CardBus is based on PCI. The switch to a more modern 32 bit bus allowed PC CardBus slots to support newer and much faster I/O technologies: including FireWire, P2 Cards, USB 1.1/2.0, and Ultra/Ultra Wide SCSI. CardBus slots accommodate legacy (16 bit) cards, but the opposite is untrue. CardBus cards are engineered with safety features that are intended to prevent insertion into legacy slots. To quickly determine if a PCMCIA PC Card is CardBus, please see our CardBus FAQ.
The reason the foregoing is important is that the various host bus technologies for Card Readers only support certain PCMCIA PC Cards. The following table should help illustrate this.
| Legacy Cards (16 bit) | CardBus Cards | |||
|---|---|---|---|---|
| Reader Bus Connection | ATA Storage | Other Storage* | I/O Cards | (32 bit) |
| Native Laptop Slot | yes | yes | yes | yes [1] |
| FireWire | yes | no | no | no |
| Floppy | yes | no | no | no |
| IDE | yes | no | no | no |
| ISA | yes | yes | yes | no |
| Parallel Port | yes | some [2] | no | no |
| PC-104 | yes | yes | yes | no |
| PCI | yes | yes | yes | yes [1] |
| USB | yes | some [2] | some [2] | some [2] |
| [1] If it has a CardBus Slot. [2] Only some models. | ||||
As seen only the system level buses (PCI, ISA, PC-104) support PCMCIA PC Card I/O functionality. In other words, read-writers for any other type bus deal with memory cards only. Furthermore, in nearly every case read-writers on non-system level buses specifically support ATA Mass Storage type cards. The few USB based based reader
When choosing between bus technologies for a card reader, alway determine the types of cards being used first. Once determined, secondary choices include
FAQ
- Contents
- Why don't CardBus capable read-writer models come in 3.5" front drive bay or external versions?
- If USB PC Card read-writers only work with memory cards, why have I seen ones that read WiFi cards?
- If USB supports devices such as modems and scanners, why not a general purpose PC Card read-writer?
Why don't CardBus capable read-writer models come in 3.5" front drive bay or external versions?
The maximum trace length for all interface signals between a CardBus controller and a card socket is 38.1mm. In other words it is an engineering impossibility to create a card reader that would allow access of 32 bit cards via a front drive bay because any such configuration would exceed that maximum.
If USB card read-writers only work with memory cards, why have I seen ones that read WiFi cards?
When WiFi (802.11b) first began widespread adoption, some vendors created USB readers that would work with their specific WiFi card. This was possible since they had complete access to their own card specification and only had to tailor the USB reader to work with their own card. Those devices could not read any other type of card than their own 802.11b cards, and have fallen out of favor for USB devices with WiFi capability built in as opposed to needing a PCMCIA PC Card. However, this is often used as an example by people as an example of how USB card readers 'should be able to read any card.' What they are not taking into account is there is a vast difference between supporting a specific devices and being able to support any device.
If USB supports devices such as modems, scanners, and printers, why not a general purpose PC Card read-writer?
Many people are confused with USB read-writers, assuming that since a wide variety of USB devices exist it should be easy to create a read-writer for a PCMCIA PC Card with similar functionality. In other words, they ask us 'if USB modems exist, why can't a USB reader work with PCMCIA PC Card modems?' While at first glance this may seem reasonable, understand that there is a difference in creating a specific device versus a generalized device that can work with any device. This is akin to asking why vendors don't create USB to PCI slot devices that can accept any PCI card and plugs into the host system via USB. However, when one looks at how complicated the engineering is to support a generalized bus such as PCI, this becomes clear. The circuitry and ASIC logic required to provide PCI on a motherboard is very complex. There are dedicated chips such as the 'South Bridge,' to provide interaction with the rest of the host computer's components. While technically feasable to duplicate this on USB or similar bus technologies, the costs of engineering and components would make such devices ridiculously complex and expensive. Furthermore, such devices could never approach the speed or reliability of existing buses such as PCI. USB 1.1 and even 2.0 buses are extremely slow and error prone in comparison to PCI. Neither consumers nor manufacturers would benefit from such a device when system level buses already exist .
