Friesen@HIS-PHOENIX-MULTICS.ARPA (05/01/88)
I have heard very different stories, I have heard that 4 Megs is a high as you can expand a 1040, I have heard that 4.5 Megs is as High as you can expand the 1040, and I have heard that 16 Megs is as high as you can expand the 1040. I heard the 4 Meg limit was due to the OS. I heard the 16 Meg limit was only possible if you cut open (to make room for the memory) the computer case, but that the limit was due to the microprocessor architecture. I didn't hear why there was a 4.5 Meg limit. Well, which is it? (thanks in advance) Aric Friesen Addresses: Genie: A.FRIESEN ARPA: Friesen%PCO@BCO-MULTICS.ARPA "Exterminate! Exterminate!"---Daleks
wes@obie.UUCP (Barnacle Wes) (05/03/88)
In article <880501040119.855327@HIS-PHOENIX-MULTICS.ARPA>, Friesen@HIS-PHOENIX-MULTICS.ARPA writes: | I have heard very different stories, I have heard that 4 Megs is a high | as you can expand a 1040, I have heard that 4.5 Megs is as High as you | can expand the 1040, and I have heard that 16 Megs is as high as you can | expand the 1040. | [...] | I didn't hear why there was a 4.5 Meg limit. | | Well, which is it? The addressing limit on the ST without hacking the hardware is 4 meg. The MMU chip does the majority of the address decoding, and it only deocodes a1..a21. If you "fall off" the end of the MMU, it will (should?) give you a bus error or address error. This could, of course, be changed by replacing the MMU chip. -- /\ - "Against Stupidity, - {backbones}! /\/\ . /\ - The Gods Themselves - utah-cs!uplherc! / \/ \/\/ \ - Contend in Vain." - sp7040!obie! / U i n T e c h \ - Schiller - wes
hase@netmbx.UUCP (Hartmut Semken) (05/08/88)
In article <215@obie.UUCP> wes@obie.UUCP (Barnacle Wes) writes: >The addressing limit on the ST without hacking the hardware is 4 meg. >The MMU chip does the majority of the address decoding, and it only >deocodes a1..a21. If you "fall off" the end of the MMU, it will >(should?) give you a bus error or address error. This could, of >course, be changed by replacing the MMU chip. No. You don't need to do that. The GLUE chip monitors -AS (adress strobe of the 68000). After a memory cycle the 68k waits for DTACK or VPA; if neithe comes, no new cycle starts, so there is no new AS. A simple monoflop, retriggered by AS, will interrupt the wait by saying "BUSERR" to her majesty. If you generate your own DTACK on your RAM board, you can easyly expand memory beyond 4 Meg. I did it; I added 2 Meg of DRAM (as resetproof Ramdisk) and 256 KByte battery backed SRAM (for fast booting) by decoding the full adress bus. hase -- Hartmut Semken, Lupsteiner Weg 67, 1000 Berlin 37 hase@netmbx.UUCP I think, you may be right in what I think you're thinking. (Douglas Adams)