On Jun 15, 2011, at 10:41 PM, Tina K. wrote: > > In theory does the SATA PCI card give higher bandwidth than the IDE/PATA > > connections, or is it still limited by the bus speed?
On Jun 16, 12:15 pm, Bruce Johnson <[email protected]> wrote: > The only communication link between the drives and the rest of the computer > is via the PCI bus, so, yes it's still bus limited. that is misleading, at best. while it is possible to purchase a HD controller that has an INTERFACE speed that is faster that the PCI bus in a MDD, in reality NEITHER the controller NOR the PCI bus i going to be the limiting factor in data transfer, unless you have a very large or very new internal RAID. like most people, if you have only one internal HD on any controller, the HD itself limits the rates of data transfer. this has been true ever since the days when SCSI-2 first became available for desktops. doesn't matter what kind of controller (SCSI, PATA, SATA), or whether it's built-in to the motherboard or in a PCI, PCI-x, or PCI-e slot. even if your HD is only a few years old, chances are it's max read/ write speeds are somewhere in the range of 60-100 MB/s. that is WAY slower than both the controller and the PCI bus. older HD's are slower still. it's easy to calculate the data transfer rate of the PCI bus, just multiply the bus width by the bus speed. you can convert bits to bytes to get numbers that are more familiar for comparison. the MDD has a 64-bit wide 33 MHz PCI bus. divide 64 bits by 8 bits/byte, and multiply by 33 MHz and you see that the PCI bus in the MDD can handle data transfer at 264 MB/s. that's more than twice the speed of the newest HD's and faster even than a lot of SSD's. it would be far more accurate to say that if you put an SSD on a SATA controller in a PCI slot, your G4 will read/write data just as fast as the newest Apple or hackintosh, being limited by the SSD itself. so, to say that data transfer is PCI bus limited is a gross over- simplification, and not just misleading, but factually incorrect. TTBOMK, the fastest IDE is ultra-133 (at 133 MB/s), which is roughly half the speed of the PCI bus. therefore, a sufficiently large internal RAID attached to an Ultra-133 controller would be limited by the controller, NOT the PCI bus. on the other hand, a SATA controller (or also an UltraSCSI-LVD at 360 MB/s) would give better theoretical performance in the PCI slot compared to an IDE (PATA) controller in the same slot. both can theoretically exceed the PCI bus speed, but remember of course, that the improvement in speed can ONLY be realized by having a sufficiently large internal RAID. -- You received this message because you are a member of G-Group, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/g3-5-list
