>From: [EMAIL PROTECTED] >Date: Fri, 14 Feb 2003 13:32:21 EST >Subject: Bus transfer speeds (was: Which ATA speed card for 8500?) > >I was just going to ask the list this, and your comments prompted me to write >right away. I was going to ask what the max transfer rate for an 8600 with a >50 Mhz bus is? You quote 133 MB/sec. Where or how did you come up with that. >The reason I ask is that a while back we were talking about this on the list, >and I tested all the drives in my 8600 both with testing programs, and my own >tests, which involve copying a 500 Meg file from SCSI, ATA and FW drives to >Ram and to each other. Besides the internal SCSI bus I also have a Sonnet >Tempo Trio. (ATA133)
132 MB/s is the theoretical maximum ignoring all arbitration overhead. It is simply 32 bit (4 bytes) X 33 MHz (speed of PCI bus) = 132 MB/s. This is nowhere near realistic because the PCI bus has one multiplexed bus for both data and addresses (uses the same 32 wires for data and addresses) so there is a fair bit of overhead to set up transactions which detracts from that theoretical maximum. Tables 1.5 and 1.6 in Apple's "Designing PCI Cards and Drivers for the Power Macintosh Computers" (Designing_PCI_Cards_Drivers.pdf) list the maximum transfer speeds that Apple tested in the x500 generation machines. The highest is 85 MB/s. The lowest is 11 MB/s. This performance depends a lot on which PCI command the PCI card uses for the data transfers. So a poorly written driver (or firmware) could give very suboptimum performance. There is also a huge gap between simple data transfer testing and actual Finder performance. Hard drives that might test at 30 - 40 MB/s in Atto's Express Tools, may only deliver 1 - 2 MB/s when copying a large number of smaller files. There's somethign up with how the Finder does file copies or something that really kills performance. I don't know what it is though. >The tech manual that came with the computer quotes a SCSI bus burst >speed of 50 MB/sec. Is the Internal SCSI bus 10 MB/sec or 10 Mb/sec? SCSI bus speeds are always listed in Megabytes per second. However, there isn't a SCSI protocol which delivers 50 MB/s theoretical. The internal SCSI bus (SCSI Bus 0) on the x500 and x600 (PowerSurge) machines is Fast SCSI-2 or 10 MB/s. It uses the Apple MESH chip which is probably a licensed version of the NCR 53CF96 which was used in the 8100. Note that the 53CF96 is different from the 53C96 found in many Quadras. Jeff Walther -- PCI-PowerMacs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Refurbished Drives | -- Sonnet & PowerLogix Upgrades - start at $169 | & CDRWs on Sale! | Support Low End Mac <http://lowendmac.com/lists/support.html> PCI-PowerMacs list info: <http://lowendmac.com/lists/pci-powermacs.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/pci-powermacs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
