CompuServe Messages

The big difference between the A2090(a) and the A2091 is their SCSI handlling. I went through this problem when I upgraded my A2500/020's HD to an 81MB Seagate ST-1096N SCSI. The older A2500's (the 68020 versions) all came with the A2090(a) controller. When doing SCSI handling in interlaced video modes, there was an incredible amount of DMA overhead introduced. It caused the video chip and the HD controller to compete for DMA time, and would basically lock up the HD. It could take several minutes to load in an interlaced image due to the conflict. The only way around it was to switch over to a non-interlaced screen, and the contention would disappear. I eventually gave up on the A2090(a), after talking to Commodore shops, and finding that they would NOT do a trade-up on it. I first tried a Kronos controller, which got rid of the DMA problem, but introduced another problem: I would be downloading, the comm software would write out to the HD, and due to it's handling, would introduce transmission errors into the dload. Finally, I got rid of the Kronos (it was fast, but the modem problems I couldn't handle) and bought a Xetec Mini-Fastcard. This is a dedicated SCSI controller, and has some advanced DMA handling routines which eliminated all contention problems! And to boot, it was about $200 cheaper than either the Kronos or Commodore's controller. Any questions? Feel free to ask… Ted