Editing MOS Technology 6581 (section)

== Revisions ==
{{unreferenced section|date=November 2011}}
[[File:SID 6581R1.jpg|thumb|6581R1 produced in 1982]]
[[File:6581 in ceramic DIP.jpg|thumb|6581 produced in 1982]]
[[File:6581R4 CDIP 1186.jpg|thumb|6581R4 CDIP produced in 1986]]
[[File:MOS SID 6582.jpg|thumb|6582 produced in 1986]]
[[File:6582A.jpg|thumb|6582A produced in 1989]]
[[File:CSG 6582A.jpg|thumb|6582A produced in 1992]]
[[File:8580R5 USA.jpg|thumb|8580R5 produced 1986 in the U.S.]]

No instances reading "6581 R1" ever reached the market. In fact, Yannes has stated that "[the] SID chip came out pretty well the first time, it made sound. Everything we needed for the show was working after the second pass." High-resolution photos of Charles Winterble's prototype C64 show the markings "MOS 6581 2082", the last number being a date code indicating that his prototype SID chip was produced during the 20th week of 1982, which would be within 6 days of May 17, 1982.

These are the known revisions of the various SID chips: (date codes are in WWYY w=week y=year format)

The SID (Sound Interface Device) chip, notable for its fusion of digital and analog technologies, was a cornerstone in the system architecture of the Commodore 64 amongst other models. The chip boasted three distinct voices each with precise and varying waveform options—it also included a 12&nbsp;dB/octave multimode filter. Over the years, the design of this filter differed with each subsequent chip revision, lending each its unique sonic fingerprint.

One of the earliest models of the SID chip, the 6581, initially found its way into Commodore 64 computers between 1982 and around 1986. This model underwent several notable revisions including the 6581 R1, a prototype model which was only seen on CES machines and development prototypes and had a date code of 4981 to 0882.<ref>{{cite web | url=https://www.polynominal.com/commodore-64-sid-6581-8580/commodore-64-sid-6581-8580.html | title=Commodore 64 SID chip }}</ref>

This model was renowned for its full 12-bit filter cutoff range and while the precise number of models produced remains unknown, it is estimated to be between 50 and 100 chips, being packaged in ceramic.

Following the R1, were the 6581 R2, 6581 R3, 6581 R4 AR, and finally, the 6581 R4. The evolution of the 6581 iterations saw minor changes to the protection/buffering of the input pins, adjustment of the silicon grade, and changes to its packaging. However, no substantial alterations were made to the filter section throughout these progressions.<ref>https://chipmusic.org/forums/topic/17495/c64-sid-shootout-6581-vs-8580/ {{Bare URL inline|date=August 2024}}</ref>

Moving to the latter models, the updated 8580 SID chipped marked its introduction in newer versions of the Commodore 64 machines. Technically compatible with the 6581 software, the 8580 brought with it a unique sound character due to specific adjustments in the filter structure.<ref>{{cite web | url=https://ist.uwaterloo.ca/~schepers/MJK/c64__.html | title=MJK's Commodore Hardware Overview: Commodore 64 }}</ref>

The sonic differences noticed between the two models, 6581 and 8580, were attributed broadly to the nuances in the analog filters, and intrinsic design distortions. These sound characteristics were heavily influenced by updates in the circuitry and quality differences in the material batches used in the various production runs of the chips.

The SID chip encompassed an ongoing journey of specifications that evolved in tandem with the chip design process. Not all initial features made it into the final blueprint. However, subsequent iterations like the 8580 model were meticulously revised to match more closely with the original specifications, specifically focusing on waveform combinations and filter functionality.

Some of these chips are marked "CSG" (Commodore Semiconductor Group) with the [[:image:Commodore logo.svg|Commodore logo]], while others are marked "MOS". This includes chips produced during the same week (and thus, receiving the same date code), indicating that at least two different factory lines were in operation during that week. The markings of chips varied by factory, and even by line within a factory, throughout most of the manufacturing run of the chip.