CompuServe Thread

Rick: Basically, Chip ram is that what can be accessed by the Amiga's custom chips (Agnus, Lisa, Paula, etc.) and the processor. Fast RAM can only be accessed by the processor, but it can do so while the custom chips are hacking away at the chip memory displaying pictures, playing sounds, etc. That's why you can play a nice MOD music file while downloading without so much as a glitch in the music. Both Chip and Fast ram are using dynamic memory. // John (Warp 4040 & Emplant Quadra 840) \X/ Mercury@ins.infonet.net

Rick, technically there is no difference between chip ram and fast ram. The chips are exactly the same. It's just that the Amiga uses both differently. On any Amiga there is a bank of chip ram and a bank of fast ram. Some Amigas (like 1200s) come with only chip ram installed. Their fast ram can be added later. So, no manufacturing differences in the chips themselves (both types can SIMM, ZIP or DIP DRAMs) but a difference in the Amiga. About your basic understanding: partly correct. When anything has to be displayed or played back, it has to reside in chip ram. Chip ram can be accessed by the custom chips that do video and sound AND by the processor. Fast ram can only be accessed by the processor. That's why fast ram is called "fast": with chip ram, the processor sometimes has to wait when a custom chip is accessing the ram; with fast ram, only the processor can use it so it never has to wait. Also, fast ram can be expanded to almost any size you wish (theoretically). Chip ram is mapped by a custom chip called Agnus, which can map 1 megabyte in the older Amigas and 2 megabytes in the newer ones. You cannot have 4 megs of chip ram. You might very well have 128 megs of fast ram however. So now you can see where your belief is wrong: when you want something displayed, you transfer it to chip ram. That is where it needs to be during display or playback, so it's NOT transferred back to fast ram. What to do when you want lots of things to display which total to more than 1 meg, without loading them from disk when needed (that would be slow)? You can store them in fast ram. Most Amigas have more fast ram than chip ram and so you follow the strategy of putting your actual program in fast ram (only the processor needs to know instructions) and storing as much data in fast ram as well, copying data to chip ram when you need it displayed or played back. "Processing" of data can occur in any type of ram, when you mean "altering data". You could for instance put your data in fast ram in compressed form and then expand it to chip ram when you need it. >F<riso Friso P. Gosliga | Auto CIS: 100341,464 – Internet: Friso.Gosliga@kub.nl | Pilot