the story of amiga | part 13 - the distress and the new chipset

the demand for greater power spawned an update in the form of the amiga 2500, which was simply A2000 (amiga 2000) fitted with a 68020 or 68030 accelerator card. still, although it was a fairly impressive mac

hine at launch, it was still not good enough for many new applications and limitations to the design meant that although the machine could be upgraded to 9MB of total RAM, the custom chipset could only directly access 512kb. Jay miner had even expressed his dissatisfaction over the somewhat pitiful improvement 2000 had actually brought, making it known that he and consumers expected and needed more.

before leaving commodore, and almost immediately after the launch of the amiga 1000, Jay had begun work on a successor to the already revolutionary chipset. this successor was code-named "ranger" and although it's widely reported to have been a brand new 32-bit architecture based around the Motorola 68010 or even 68020 CPU, it was more of an increase to the expansion capabilities of the original chip-set. these were really the capabilities that came to

fruition in the amiga 2000 itself, leaving the actual base chipset not quite as advanced by 1989 as they were some 4 years prior.

with the original chipset limited to accessing just 512kB of chip RAM, later iterations for the amiga 500 and 2000 introduced the Fat Agnus chip, which allowed an additional 512kB pseudo-fast RAM upgrade that could only be accessed by the 68000 CPU, but crucially only because of this it's commonly referred to as slow RAM, and it's not tied to Agnus, its use is somewhat limited if you want to store data directly from the custom chipset, such as GFX or sound data for example. this was essentially a hack of the original chipset, but the next version would circumvent this limitation by employing a new fatter Agnus chip (also known as obes

e Agnus), but it's also the point where things get a little bit messy.

fatter Agnus is capable of addressing 1mB of chip RAM directly and was fitted to amiga models in 1989 from revision 6 onwards - although some of these machines require jumper changes to fully enable this. these changes sometimes referred to as the "half enhanced chipset" were made unbeknownst to the average consumer at the time were followed by a range of minor board revisions culminating in the arrival of the full enhanced chipset in 1990. although an incremental update, this chipset is really the official second generation of Amigas.

that's all for part 13. part 14 can be found here