johnmac@fawlty.towers.oz (John MacLean) (11/13/90)
In article <4867@sage.cc.purdue.edu> you write: >My question is about DMA not amount of ram. Everyone says the GS can >only handle 4 megs of DMA ram (8 megs total). I have a rom 1 GS (256K) >and a 4 meg ramcard (supports DMA) thus giving me 4.25 megs of memory. >Of this 4.25 megs, can DMA access all of it or is the last 256K on the >ramcard non-DMA? >-- > Y_,_|[]| Eric Mulholland >{|_|_|__| ericm@sage.cc.purdue.edu >//oo--OO ...!pur-ee!sage.cc!ericm The responses up until now have been somewhat confusing, so I'll try and clarify things: Any memory on the motherboard is accessable via DMA. The DMA limitation is 4 banks of chips on your *memory expansion card*. Anything beyond this is not accessable via DMA. With 256K chips in your memory expansion card: - With a ROM1 you can DMA up to 1.25 Meg. - With a ROM3 you can DMA up to 2.125 Meg. Thus with 1 Mbit chips in your memory expansion card: - With a ROM1 you can DMA up to 4.25 Meg. - With a ROM3 you can DMA up to 5.125 Meg. I presume if you had 4 Mbit chips (Simms I guess, I do not think anyone makes a GS card that takes 4 Mbit chips), you could DMA the whole eight megabytes. The boundary condition as to what happens over the 8 meg line if you had 8.25 or 9.125 Meg is beyond me - I'll let you know when I get another 7 Meg. Hope that is somewhat clearer. John MacLean. -- This net: johnmac@fawlty.towers.oz.au Phone: +61 2 427 2999 That net: uunet!fawlty.towers.oz.au!johnmac Fax: +61 2 427 7072 Snail: Tower Technology, Unit D 31-33 Sirius Rd, Home: +61 2 960 1453 Lane Cove, NSW 2066, Australia.
ifar355@ccwf.cc.utexas.edu (David H. Huang) (11/14/90)
In article <526@fawlty.towers.oz> johnmac@fawlty.towers.oz (John MacLean) writes: |I presume if you had 4 Mbit chips (Simms I guess, I do not think anyone |makes a GS card that takes 4 Mbit chips), you could DMA the whole eight |megabytes. The boundary condition as to what happens over the 8 meg line | |John MacLean. |-- |This net: johnmac@fawlty.towers.oz.au Phone: +61 2 427 2999 |That net: uunet!fawlty.towers.oz.au!johnmac Fax: +61 2 427 7072 |Snail: Tower Technology, Unit D 31-33 Sirius Rd, Home: +61 2 960 1453 | Lane Cove, NSW 2066, Australia. Does that mean all current RAMcards that use Simms will be able to take the 4 Meg ones? I've always seen them advertized as taking 1 Meg simms. Having 8megs of DMA ram would be pretty neat! :-) ---Dave Huang -- David Huang | "I didn't order any Internet: ifar355@ccwf.cc.utexas.edu | pizzas, especially America Online: DrWho29 | green ones"
toddpw@nntp-server.caltech.edu (Todd P. Whitesel) (11/14/90)
ifar355@ccwf.cc.utexas.edu (David H. Huang) writes: >Does that mean all current RAMcards that use Simms will be able to take the >4 Meg ones? I've always seen them advertized as taking 1 Meg simms. Having >8megs of DMA ram would be pretty neat! :-) Sorry, it won't work that way. Current SIMM cards only take 256K or 1 Meg SIMMs. A card that took 4 meg SIMMs would have to do the same sort of acrobatics to ensure DMA compatibility. It could be done, but I haven't seen a product yet that does. Todd Whitesel toddpw @ tybalt.caltech.edu
gwyn@smoke.brl.mil (Doug Gwyn) (11/16/90)
In article <526@fawlty.towers.oz> johnmac@fawlty.towers.oz (John MacLean) writes: >The boundary condition as to what happens over the 8 meg line >if you had 8.25 or 9.125 Meg is beyond me - I have 8MB on a memory expansion card and 0.25MB on the motherboard. Only 8MB of RAM is accessible due to the addressing structure of the IIGS. This is described in the Apple IIGS Hardware Reference manual, which also tries to insist that only the lower 4MB will work (simply not true).
gwyn@smoke.brl.mil (Doug Gwyn) (11/16/90)
In article <39640@ut-emx.uucp> ifar355@ccwf.cc.utexas.edu (David H. Huang) writes: >Having 8megs of DMA ram would be pretty neat! :-) However, Apple's DMA SCSI card would still not perform DMA involving addresses beyond th4 lower 4MB.