This 6000 x ATM software refresh is not taking 3 years - it's being done by several hundred field engineers. It started in early October and will end before Christmas 2011. There is a larger 3-year program to deliver additional capability through ATMs. This has been publically announced.
If I were doing it I wouldn't do so by HDD replacement or loading from an external HDD. For bandwidth reasons it doesn't make sense to push it out over the internal ABSA ATM network. If I were ABSA management I'd insist - for security reasons - that writable media cannot be used in any way whatsoever. The best way, all things considered: Create master images created in a highly secure environment; write and replicate them to read-only optical media in an encrypted form, and then deploy to the ATMs by field engineers, totally overwriting the original disk. Make sure there is absolutely minimal user interaction by the field engineer when deploying the image. Also, incorporate various security checks to ensure the image (and only the image) is written to disk, and no other software is introduced into the system. The security checks shold be as tight as technology and human controls can make it.
There is a wide range of machines.