Thin Clients: Compact Flash Adaptors 

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Compact Flash Adaptors

IDE and DOMS

Most thin clients use a DOM (Disk On Module) to carry the system firmware. Generally these plug directly into a standard 44-pin IDE interface. An example of a fitted DOM is shown on the right. In general the IDE interface can generally be found close the edge of most thin client motherboards.

One important thing to note - which can be seen in the photographs below - is that: Looking at the IDE interface with the board edge behind it, pin 1 is always at the right-hand end of the connector. In the example below this is indicated by the diagonal corner on the white printed rectangle surrounding the IDE connector. (You can also spot the printed '2' to the right aligning with pin 2 of the connector).

If you want to fit a larger DOM you can often find they cost more than you paid for the thin client in the first place! I tend to use Compact Flash cards as (a) The digital cameras I've used over the years have used them so I now have plenty of spare cards of varying capacities lying around; and (b) they're relatively cheap.

CF Adaptors

Checking on eBay you'll find that there are plenty of Compact Flash adaptors available, both for 40-pin and 44-pin IDE interfaces. In the former case they'll be an additional socket for providing power to the card. This is not necessary with the 44-pin connector as power is supplied through the standard interface. Three typical 44-pin examples are shown below (top and bottom views):

Looking at each in turn:

• Top: This is a double sided adaptor that supports two Compact Flash cards. I have found these to be of variable quality and a bit hit-and-miss as to whether you can actually use two Compact Flash cards. With one that I had in daily use the second Compact Flash card suddenly vanished after about a year of use. (The card was still fine, it was just that nothing worked any more in the second socket of the adaptor).
  
  
• Left: At first glance these look ideal as a drop-in replacement for a DOM - no cable required - but they are not - as a number of people have found out. If you look closely at the one in the left-hand photograph you can see that pin 1 (as indicated by the diagonal corner stripe on the silk-screened rectangle) is at the left-hand end of the board as pictured - the opposite end to a standard DOM in the same orientation. This means that as a DOM replacement it has to be fitted the other way round with the circuit board and Compact Flash card on the other side of the IDE connector. As the IDE interface is always close to the edge of the motherboard, the only way you can make this work is by cutting a suitable hole in the thin client's metalwork and case! (I have never done this)
  
  
• Right: This is bog standard single Compact Flash card adaptor with a 44-pin male interface. This connects to the IDE interface with a short cable (see picture below) and all you have to ensure is that pin 1 on the cable (usually marked with a red stripe) connects to the pin 1s on the respective connectors. (Once again look for the diagonal stripe on the corner or may be a '1' or a '2'. You may also find a silk-screened '44' at the other end of the connector).

Whatever Compact Flash adaptor you find and try and use, do check that you connecting pin 1 on the adaptor to pin 1 on the IDE interface. Most thin clients just use two rows of pins on the motherboard without any surrounding socket or keyway. In those circumstances it is easy to get it wrong.

NB: I have no idea why the manufacturers in the Far East do not make a Compact Flash adaptor that mirrors the standard DOM in its physical orientation. Maybe they will someday, but for now, every one I've seen advertised on eBay has been back-to-front as far as our needs are concerned.