User manual

Cypher Technology Ltd 2008
18
Where RAW image files are detected, the system automatically converts them to a
JPEG compressed image file with a compression ratio of about 7:1. The file has the
same root name as the original, so that dcn0005.nef becomes dcn0005nef.jpg. For
most picture content it will not be possible to readily observe any difference in quality
between the JPEG and RAW images. Where this feature is not required, it may be
disabled (see above).
A wide range of RAW file formats are supported and these are listed in the Appendix.
5.4 Card and Disk Checksum
Puma produces a 32 bit checksum of the Flash card and Master Copy file. The
checksum is a unique number derived from all the data on the card or from the whole
image file on the Master Copy. As such the checksum will always change if any data
changes are made within the file or on the card. The chance of two Flash cards, with
different image data, of having the same checksum is 1 in 4,000,000,000.
The checksum of a Flash card or Master Copy can be found using the Menu functions
(see above).
5.5 Flash Card Wipe (Erasing)
As mentioned above, when a file is deleted the file data remains on the medium. This
file may be un-deleted and the file’s data recovered. The only way to render the card
safe from data recovery is to re-write the whole card with new data. Puma “Wipe Card”
function writes binary zeros to the whole card. Also viruses may be present in the
Master Boot Record (MBR). During the wipe process the MBR is overwritten also and is
recreated during the format operation.
5.6 System Architecture
Puma is based on a Linux platform and uses proprietary software. The proprietary
nature of the software has allowed the transfer process to be tailored precisely to the
needs of law enforcement and evidence gathering. For maximum reliability and security
it contains no hard disk and boots from a read-only Flash file system.
5.7 Transfer Times
The Media Transfer Station uses a full height, high performance CD/DVD writer drive.
This type of drive provides transfer rates up to 20 Mbyte/sec compared with 8Mbyte/sec
for laptop drives. Also, the larger size of the drive provides a higher reliability disk.
Further time is saved during the transfer as the separate tasks (Transfer, Verify and
Erase) are started automatically, one after the other. The user does not have to open
separate applications for disk imaging, file copy, file verify, raw file conversion and Flash
erase. Clearly for the user to run these five programs manually in sequence would
require considerable time and perhaps more important, be prone to error. A single,
automated process avoids these sources of error and saves time.
For reading, the maximum transfer rate (at he outside of the disk) is about 20
Mbytes/sec. A 4 Gbyte card can be copied in about 4 minutes.