upsiu@mcs.drexel.edu (Paul Siu) (04/27/91)
I have been doing some research into Accelerators for an SE. I like someone to answer the following questions. 1) With a 68030 accelerator, or a 68020 accelerator with a PMMU. Can virtual access more than 16 Meg under System 7.0. I know that you cannot use System 7's virtual memory on an accelerated SE, but can third party products like Virtual, and Maxima access more than 14MB of virtual memory under System 7? 2) Most products will claim higher speed in raw processing, but almost none of them claims to speed up SCSI. Will I see an improvement in disk access when I install an accelerator? Does disk access on the Mac II seem faster because of the faster cpu, or is it because the SCSI transfer rate is faster overall? Here's what I gather so far from my research: - Accelerators come in different flavors. Most consist of a board that plugs into the SE's slot. Dove's processor clips on the SE's cpu. - Accelerator may come with its own RAM. Gemini, Novy, MacProduct, NewBridge and others all have SIMM sockets on their board. You can move the memory you have on your Mac to the accelerator (which means you have to reinstall the 256K SIMMs, and resolder a resistor). But to take advantage of the full capability, you have have faster simms (about 70ns for 25MHZ models). Some models allow you to add up to 16MB of memory using 4MB simms. The SE however can only address up to 4MB, and use the rest as RAM disk, though some software like Maxima can use it as virtual memory. - Dove and Radius accelerator uses a 32K static Ram as a cache between the accelerator and the Mac SE Ram. Note that this is true only on the new Dove Marathon Racer 030SE. The older Dove Marathon only has no static cache and only had a 35% speed improvement. - Almost all of the accelerator cards have capability for video expansion. The Dove model does not, but the Dove model leaves the SE slot free. - Almost all of the board requires you to have low-profile SIMMs. Most expansion cards will not fit in an SE with Dip simms. - None of the accelerator board accelerate SCSI transfers. - Compatibility seems to vary. Many Macintosh device such as the floppy drives are time dependant. Accelerators must slow down every time you format a diskette. Some like the Gemini will automatically slow down the accelerator, others like the NewBridge boards must be turn off manually. Some strange odd-ball boards. - Newbridge claims that their board is System 7 virtual memory compatible. I find that hard to believe, especially since their salespersons gave contradicatory data. - Brainstorm has a new accelerator for the Mac plus that replaces two chip on the Plus's motherboard. One of the chip is a timing chip that will speed up SCSI, and memory access. A 68020 version is coming out for the SE, and it is upgradable to 68030. They claim that the timing chip can speed up the SCSI to as much as 5x (with fast hard drives). They claim no software incompatibility, but they couldn't answer a lot of questions about it either. I thank you for any response. Paul Siu upsiu@mcs.drexel.edu