David Cook
Well-known member
I picked up a Macintosh II with a surprise inside: The Sonnet Allegro Doubler Mac II. The board has a 68030 processor fed double the native clock (15.6672->31.3344) which is marketed as 16 MHz -> 33 MHz.
Besides the speed bump, the other benefit is that the 68030 includes a built-in MMU. This overcomes the limited functionality of the black Apple MMU (upper left of the picture above) and thus a replacement 68851 PMMU is no longer required. If you have GAL-based 4 MB SIMMs and upgraded ROMs, then the Mac II can use more than 8 MB of memory.
There is a slightly futuristic heatsink on the CPU. Other people have reported pulling off the heatsink to discover the CPU that Sonnet used was not officially rated for 33 MHz. Maybe the heatsink is necessary for overclocked parts?
The underside is sparse. It has a 68020 pinout to connect to the 68020 socket on the Mac II motherboard. There is a similar Sonnet board with a 68030 pin connector for the SE/30 and IIx. They are not interchangeable.
My board would not post (no chime or display) when I received it. Some other people have reported similar fates. The middle area of the top of the board seems to have received a little less solder than everywhere else. I reflowed the pins and pads in that area. However, for me, the root cause was a loose external SCSI terminator that the eBay seller tossed into the Mac II case which apparently banged around during shipping. Notice a bent/lifted pin in the image below?
The Sonnet Doubler results in about a 50% boost in performance. That doesn't seem like a lot, but for a relatively slow computer it is noticeable.
Here is the advertisement from Sonnet.
And below is what I measured. 148% in both cases! How honest. For comparison, @zigzagjoe 's Interware Booster clone for the IIx runs faster -- and includes a faster FPU.
The detailed ratings show that CPU clock boosters are limited by main memory performance.
Peeking at the performance of the 68030's built-in 256 byte data cache, we can see the full clock speedup when main memory is not involved. (The 68020 has an instruction cache but no data cache.)
I ran my tests on System 7.1 with the Sound Manager extension removed and with the Sonnet Allegro extension 1.2 added. Notice above, that the lack of an Allegro extension has a tiny negative effect on performance (the far left of the graph). I ran the tests multiple times to confirm the effect was real. The extension may also increase compatibility.
The Macintosh startup sound runs at double speed. But, no other sound issues were noted. Again, I removed Sound Manager as it likely plays the sounds from code in RAM, rather than the ROM location that the Allegro card knows to slow down for.
The floppy drive on this Mac II did not work, so I did not have the chance to test it. Other people have indicated that the floppy drive cannot be used for booting, as the Allegro extension (?) can't fix floppy disk access until after the extension is loaded.
All in all, it was fun playing with this. But, the limited boost is not worth the potential incompatibility in my opinion. Don't bust your bank account bidding this up on eBay.
- David
Besides the speed bump, the other benefit is that the 68030 includes a built-in MMU. This overcomes the limited functionality of the black Apple MMU (upper left of the picture above) and thus a replacement 68851 PMMU is no longer required. If you have GAL-based 4 MB SIMMs and upgraded ROMs, then the Mac II can use more than 8 MB of memory.
There is a slightly futuristic heatsink on the CPU. Other people have reported pulling off the heatsink to discover the CPU that Sonnet used was not officially rated for 33 MHz. Maybe the heatsink is necessary for overclocked parts?
The underside is sparse. It has a 68020 pinout to connect to the 68020 socket on the Mac II motherboard. There is a similar Sonnet board with a 68030 pin connector for the SE/30 and IIx. They are not interchangeable.
My board would not post (no chime or display) when I received it. Some other people have reported similar fates. The middle area of the top of the board seems to have received a little less solder than everywhere else. I reflowed the pins and pads in that area. However, for me, the root cause was a loose external SCSI terminator that the eBay seller tossed into the Mac II case which apparently banged around during shipping. Notice a bent/lifted pin in the image below?
The Sonnet Doubler results in about a 50% boost in performance. That doesn't seem like a lot, but for a relatively slow computer it is noticeable.
Here is the advertisement from Sonnet.
And below is what I measured. 148% in both cases! How honest. For comparison, @zigzagjoe 's Interware Booster clone for the IIx runs faster -- and includes a faster FPU.
The detailed ratings show that CPU clock boosters are limited by main memory performance.
Peeking at the performance of the 68030's built-in 256 byte data cache, we can see the full clock speedup when main memory is not involved. (The 68020 has an instruction cache but no data cache.)
I ran my tests on System 7.1 with the Sound Manager extension removed and with the Sonnet Allegro extension 1.2 added. Notice above, that the lack of an Allegro extension has a tiny negative effect on performance (the far left of the graph). I ran the tests multiple times to confirm the effect was real. The extension may also increase compatibility.
The Macintosh startup sound runs at double speed. But, no other sound issues were noted. Again, I removed Sound Manager as it likely plays the sounds from code in RAM, rather than the ROM location that the Allegro card knows to slow down for.
The floppy drive on this Mac II did not work, so I did not have the chance to test it. Other people have indicated that the floppy drive cannot be used for booting, as the Allegro extension (?) can't fix floppy disk access until after the extension is loaded.
All in all, it was fun playing with this. But, the limited boost is not worth the potential incompatibility in my opinion. Don't bust your bank account bidding this up on eBay.
- David
