DSP?

[ChristTrekker]

What exactly do the DSPs in those AV machines do? Are they basically like a special-purpose CPU for offloading certain tasks to? Is there any documentation on them?

 

[Unknown_K]

Plenty of documentation out there, mostly used for video and audio work, some JPG compression. I got a Nubus card a few weeks back with a huge DSP on it for creating outputs in labview (National Instruments card).

 

[Bunsen]

The lowendmac machine profiles for the 660AV and 840AV should be a good start.

 

[tomlee59]

What exactly do the DSPs in those AV machines do? Are they basically like a special-purpose CPU for offloading certain tasks to?

Short answer is Yes. Think of them as media-specific coprocessors. They get more of those specific tasks done per clock cycle than do general-purpose CPUs.

 

[Quadraman]

In certain applications a DSP is as good as a second CPU. Processors with highly specialized functions were sometimes used in computers before multiple processors became mainstream to take some of the load off of the CPU. As CPU speeds got faster and costs got lower, the DSP wasn't a good value for speeding up specialized applications anymore. It was better to have a second CPU instead. The Nubus PPC machines offloaded everything to expansion cards if you had them, though, because Apple didn't create a direct replacement for the AV models, which was kind of a drag because if you traded in your 660AV or 840AV on a 6100, 7100 or 8100 you also had to seek out a card to replace the functionality of the DSP, which was pretty much impossible in the case of the 6100 with it's one oddball slot that required a 90 degree adapter to get anything to fit it. A lot of 660AV's and 840AV's remained in service until the dual CPU PCI machines came out and it's one of the reasons they go for such high prices today.