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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 often widely used to refer to different CPC models.:

* Arnold 4 - costdown CPCs (the 100pin ASIC chip is marked "ARN4" in costdown schematics [http://www.cpcwiki.eu/manuals/Amendment%20Service%20Manual.rar Amendment Service Manual], page 20)* Arnold 5 - CPC Plus ( There are several variations: Some webpages omit the [[Original Arnold V Specs]] costdown CPCs (and refer to the CPC Plus [or as Arnold 4). Other webpages split Plus to its 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 chip?] as ", 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 (costdown 100pin SMD version)* Arnold 5 - Gate Array (plus 160pin SMD version) === Overall Numbering === 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. === References ===

Actually, * Arnold 1-3 ''might'' also refer to the three Gate Array revisions, 40007, 40008, and 40010- There are no (known) official docs mentioning these numbers. ''* Arnold 4 - The 100pin ASIC chip is marked "ARN4" in costdown schematics [Are there any official documents on http://www.cpcwiki.eu/manuals/Amendment%20Service%20Manual.rar Amendment Service Manual], page 20)* Arnold 15 -3?CPC Plus (the [[Original Arnold V Specs]''] refer to the Plus/ASIC as "Arnold V")