roland@bruce.oz (Roland Yap) (10/04/88)
I am wondering what are the real advantages of having a 68030 in a mac IIx.
I mean are there instructions significantly faster, new instructions, etc.
After all one can get a MMU for the mac II so why would there be much
advantage CPU-wise for a IIx, ignoring the speed difference of the 68882.
Also are there any other intrinsic hardware enhancements besides the Superdrive.
Roland
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Roland Yap ACSNET:roland@moncsbruce.oz
Dept. of Computer Science ARPA,CSNET:roland@moncsbruce.oz.au
Monash University UUCP: ..!seismo!munnari!moncsbruce.oz!roland
Clayton ...!{decvax,pesnta,vax135}!mulga!moncsbruce.oz!roland
Australia 3168gillies@p.cs.uiuc.edu (10/05/88)
Maybe the 68030 in the Mac IIx benefits APPLE, not the customer - Perhaps Apple wanted to get a jump on Sun & NeXT, so they could claim "We have a 68030 machine". - The Apple MMU & Socket cost $$$ in manufacturing (there is a stub MMU in a regular Mac II without the 68851) -- this money can be saved in a 68030 machine. - There is only 1 configuration of IIx system board (no sockets), so board swaps are simpler, inventory is simplified (no 68851's to stock). Or, maybe it benefits A/UX customers - Is it true that 68030 $$$ <= 68020 $$$ + 68851 $$$ ? - The 68851 is a SLOW paging chip -- it adds 1 wait-state to A/UX memory references. Sun/etc. get around this with their own PMMU designs. Does the 68030 have this wait state? If not, then putting the 68030 in the IIx speeds up A/UX (but not the Mac O/S).
daveh@cbmvax.UUCP (Dave Haynie) (10/06/88)
in article <76000295@p.cs.uiuc.edu>, gillies@p.cs.uiuc.edu says: > Nf-ID: #R:bruce.oz:578:p.cs.uiuc.edu:76000295:000:833 > - The 68851 is a SLOW paging chip -- it adds 1 wait-state to A/UX memory > references. Sun/etc. get around this with their own PMMU designs. Does > the 68030 have this wait state? If not, then putting the 68030 in > the IIx speeds up A/UX (but not the Mac O/S). The 68030 MMU does its translations fully in parallel, so as long as your translation is in the ATC, or the MMU's shut off, no delay results. The '851 adds a wait state whether it's translating or not. On the other hand, the '851 ATC is 64 entries, whereas the '030 ATC is only 22 entries. Whether or not the MacIIx speeds up memory-cycle-wise over the MacII really depends on where the MacII's extra wait state came from. If it really was from the MMU alone, it should go one cycle faster. If it was an artifact of the memory system design, no change. The 15% speeup they quote sounds to me more like a data cache speedup; does the normal Mac OS permit the data cache to be enabled? -- Dave Haynie "The 32 Bit Guy" Commodore-Amiga "The Crew That Never Rests" {ihnp4|uunet|rutgers}!cbmvax!daveh PLINK: D-DAVE H BIX: hazy "I can't relax, 'cause I'm a Boinger!"