ask THE SCSI EXPERT.Visit the SCSI SCSI in full Small Computer System Interface Once common standard for connecting peripheral devices (disks, modems, printers, etc.) to small and medium-sized computers. SCSI has given way to faster standards, such as Firewire and USB. Trade Association's web site (www.scsita.org) to ask the SCSI Expert a question. Q : Are the theoretical predictions of the sacs data transfer (max) sustained at all times or is it just at burst intervals? For example, if you had a Fast SCSI A SCSI interface that transfers at 10 Mbytes/sec rather than 5 Mbytes/sec. The maximum cable length is 9.8 feet. See SCSI. (hardware) Fast SCSI - A variant on the SCSI-2 bus. It uses the same 8-bit bus as the original SCSI-1 but runs at up to 10MB/s - double the speed of SCSI-1. (10MB/sec) is it 10MB/sec at all times or is it somewhere between 0-10MB/sec? Also, since the SCSI interface SCSI interface - SCSI adaptor is intelligent, could you connect a slower SCSI drive to a faster one and assume that each will perform at its maximum capacity? A: The often quoted Fast SCSI data rate of 10MB/sec is the maximum data rate. As there is a small amount of overhead associated with SCSI, 10MB/sec cannot really be achieved. While the Fast SCSI bus is capable of 10MB/sec for narrow SCSI (20MB/sec for wide SCSI A SCSI interface that transfers 16 bits in parallel rather than 8 bits. See SCSI. (hardware, standard) Wide SCSI - A variant on the SCSI-2 interface. It uses a 16-bit bus - double the width of the original SCSI-1 - and therefore cannot be connected to a SCSI-1 bus. ), actual throughput is dependent on many factors. SCSI's "intelligence" allows devices to communicate with one another at the data rate of the slowest device. For instance, a Fast host adapter Also called a "controller" or "host bus adapter," it is a device that connects one or more peripheral units to a computer. It is typically an expansion card that plugs into the bus. IDE and SCSI are examples of peripheral interfaces that call their controllers host adapters. See host. will communicate with a Fast peripheral at its speed, but will communicate with a Slow peripheral at its speed. Further, if the Fast peripheral had to communicate with the Slow peripheral, they would pass data at the Slow speed (with no host intervention; that is another feature of SCSI "intelligence"). After the SCSI bus has booted, the host and all the peripherals know the speed at which all other devices can pass data. Q: Is it possible to run an Ultra2 Wide device (hard disk) on a "normal" Ultra Wide host adapter (regardless of performance)? A: The Ultra2 drives are multimode; they will only run Ultra2 LVD See LVDS. LVD - Low Voltage Differential SCSI when they are attached to a bus that is Ultra2 or newer. If they are connected to Ultra Wide single ended (hardware) single ended - An electrical connection where one wire carries the signal and another wire or shield is connected to electrical ground. This is in contrast to a differential connection where the second wire carries an inverted signal. , the drive will switch to single ended SCSI at the Ultra speed. Q: In the process of e upgrading my facility, I bought a new computer. This computer came with a single channel Ultra2 Wide controller and a 7200rpm Ultra2 Wide internal drive. However, I need to migrate my legacy SCSI devices to this new machine. I have an internal Fast, Narrow SCSI-2 tape backup Using magnetic tape for storing duplicate copies of hard disk files. Users can add an internal or external tape drive to their desktop computers for backup purposes, and files are typically copied to the tapes using a backup utility that updates on a periodic schedule. , an external SCSI-2 scanner, an external SCSI-2 Zip drive See Zip disk. (hardware, storage) Zip Drive - A disk drive from Iomega Corporation which takes removable 100 megabyte hard disks. Both internal and external drives are manufactured, making the drive suitable for backup, mass storage or for moving files between computers. , and an external Ultra Wide hard drive. How should I connect all these varying devices? Should each speed be on a different channel (i.e., buy a new dual-channel card, as well, and have two cards in the system)? Will a slower speed device affect performance of a faster device if they are on the same channel? A: I would recommend a second SCSI adapter. There are too many narrow devices and there is a loading problem. You can connect the devices to the Ultra2 bus, but it will switch everything to single ended mode with reduced performance. You may have to load compensate the high byte with that many narrow devices on the bus. If you have an Adaptec AHA2940 or 2930, they have expanders for the single ended device on the adapter card. Q: I have an adapter that claims to have "high line" termination. Is this the same as "high byte" termination? Would you use the same type of adapter (i.e., same type of termination) to go from Wide devices to narrow buses and vice versa VICE VERSA. On the contrary; on opposite sides. ? A: High Line termination is not a term that is normally used. It should state High byte termination. It is most likely the same thing, but I would question the supplier. Q: Is there a specific type termination required for LVD drives or can a standard UltraWide Active terminator be used? A: LVD SCSI buses require either an LVD Only or Multimode (LVD/MSE) terminator. The standard terminator will convert the whole bus back to single ended Ultra SCSI speed and bus limits. LVD SCSI runs Ultra2, Ultra3, and Ultral60 devices currently. All devices must be LVD SCSI for the bus to run the higher speeds. |
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