Arnold is Amstrad's internal codename for the CPC computers.
In the BIOS ROM the string "Arnold" is found as a (non-selectable) leading dummy-entry in the list of LK-selectable Brand Names.
Amstrad used some kind of an "Arnold Numbering System" for revisions of the CPC hardware. The "official" meaning of that numbers is unknown, and there a several different "homebrewn" interpretations:
Numbering for CPC Models
Arnold 1-5 are widely used to refer to different CPC models:
- Arnold 1 - CPC 464
- Arnold 2 - CPC 664
- Arnold 3 - CPC 6128
- Arnold 4 - costdown CPCs
- Arnold 5 - CPC Plus
There are several variations: Some webpages omit the costdown CPCs (and refer to the Plus as Arnold 4). Other webpages split Plus to separate numbers (Arnold 5 for 464+, and Arnold 6 for 6128).
Numbering for Gate Array Versions
Looking closer at the two offical docs, ARN4 refers to the 100pin ASIC, Arnold V describes the 160pin ASIC. So it seems more likely that Amstrad was using the Arnold Numbers to refer to Gate Array Versions, rather than to the computer models:
- Arnold 1 - Gate Array 40007 (old version with cooling-plate)
- Arnold 2 - Gate Array 40008 (rare medium version)
- Arnold 3 - Gate Array 40010 (newer version)
- Arnold 4 - Gate Array 40226 (costdown 100pin SMD version)
- Arnold 5 - Gate Array 40489 (plus 160pin SMD version)
Finally, it's possible that both of the above numbering systems are correct - the different Gate Array versions were developed alongside with the different computer models - so the numbers may have originally referred to both chips & computers. Although later on, the 40010 Gate Array was also used in 464/664, rather than in 6128 only.