--- Desert Fox <[EMAIL PROTECTED]> wrote: > on 2/20/04 3:55 PM, Gregg Eshelman at > [EMAIL PROTECTED] scribbled: > > > Have you tried them with something like a > Jackhammer > > wide SCSI card? I don't know if one of those would > > be fast enough on NuBus. > > Actually, I was testing them out on a PCI PowerMac > with a G3 upgrade in it > on both the fast SCSI bus as well as an Adaptec PCI > SCSI card. Same crappy > throughput no matter where I stuck it. > > Are there any SCSI controllers out there that have > an 80 pin connection? > What boxes use SCA drives without the adapters to > throttle down to 68 or 50 pin?
Ahhhhh. I assumed NuBus since this is the Vintage Macs list. You need a SCSI drive chassis made for use with SCA drives for a server, then a card that's Mac compatable to connect to the PCI bus. SCA 80 drives are the 68 pin Wide interface, plus lines for remotely setting SCSI ID from 0 through 15, turning on/off spindle syncronization and some other things. 10K RPM drives are most likely Ultra Wide and need an Ultra Wide capable controller. SCSI 1 and SCSI 2 are 8 bits wide and transfer up to 5 megabytes per second. Fast SCSI 2 is 8bits wide and transfers data at speeds up to 10 megabytes per second. It does this by doubling the data clock rate. Fast/Wide SCSI doubles the rate to 20 megabytes by expanding the bus width to 16 bits and runs at the same clock rate as Fast SCSI 2. Ultra SCSI is 8 bits wide and doubles the clock rate of Fast SCSI 2 to cram 20 megabytes through the narrow SCSI 50 pin cables. Like other narrow versions, this only supports 7 SCSI IDs. Ultra/Wide SCSI runs the same clock rate as Ultra SCSI and does up to 40 megabytes, 16 bits wide. Faster versions of Ultra SCSI that use the 68 wire cable get their speed gains over 40 megabytes per second through even higher data clock rates. If your Mac is running the PCI bus slower than 33Mhz you'll be limited on how fast data can transfer to and from SCSI drives through any controller attached to the bus. I dunno if the onboard controllers go through the PCI bus or not. PCI at 33Mhz has a max transfer rate of 133 Megabytes per second. That's the maximum for the whole bus, and you have more than one device contending for the bandwidth. Depending on the computer there may be more than one PCI bus, especially if there are more than three slots, which is all PCI was originally designed for. Newer updates to PCI have allowed up to 5, maybe more slots/devices per bus. PCs typically use a PCI-PCI bridge to connect the busses together. I dunno what the Macintosh term is for that. Another thing to consider with PCI on Macs is that PCI is always a Little Endian* bus. Macs run their CPU and other hardware as Big Endian, therefore all data transfers to and from PCI devices must have the byte order "flipped", which adds clock cycles to the process and may impact on actual data transfer rates. *Since PCI is mostly an Intel invention. Soooo, if your Mac's PCI bus isn't running at 33Mhz, "overclock" it to that and see if your SCSI improves. And further questions on the subject may be better targeted to the Mac-n-DOS list. :) ===== Say hello to Juror #49. Yep, I'm on jury duty until the end of March. Gotta call in each weekend. Fun. __________________________________ Do you Yahoo!? Yahoo! Mail SpamGuard - Read only the mail you want. http://antispam.yahoo.com/tools -- Vintage Macs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Enter To Win A | -- Canon PowerShot Digital Cameras start at $299 | Free iBook! | Support Low End Mac <http://lowendmac.com/lists/support.html> Vintage Macs list info: <http://lowendmac.com/lists/vintagemacs.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/vintage.macs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
