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: Is it possible to attach an Ultra2 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. drive to an Ultra Wide SCSI adapter card? Or must I upgrade the adapter card to Ultra2 SCSI first? I understand that performance will be limited to Ultra Wide SCSI, if this is even possible. A: The drives will o switch to Ultra Wide single-ended SCSI. The Ultra2 SCSI drives do not have termination, so therefore you must have termination in the cable system. I recommend upgrading the adapter only if you are running multitasking multitasking Mode of computer operation in which the computer works on multiple tasks at the same time. A task is a computer program (or part of a program) that can be run as a separate entity. with three or more disk drives. Q: Would like to move LVD See LVDS. LVD - Low Voltage Differential SCSI. I've located the appropriate drive and controller. I've heard that twisted pair and untwisted un·twist v. un·twist·ed, un·twist·ing, un·twists v.tr. To loosen or separate (something twisted) by turning in the opposite direction; unwind. v.intr. To become untwisted. , flat internal cables are LVD cables. I know that on HVD (1) (High Voltage Differential) See SCSI and differential signaling. (2) (Holographic Versatile Disc) A high-capacity optical disc from the HVD Forum (www.hvd-forum. , twisted cables are required. Are flat and twisted pair cables correct on a LVD bus? My LVD bus will be three feet or less. A. It is true that either twisted pair or non-twisted pair internal ribbon cables can meet the SCSI spec. However, this same SCSI spec highly recommends the use of twisted pair cables on faster versions of SCSI. There is a crosstalk problem with the flat cable. The flat cable should only be used in very limited configurations with two drives and less than two feet. As long as you have a choice, buy the twisted pair cables. You are less likely to have noise problems. Q: What effect does the device numbering have on the device's physical location on the SCSI chain? Does internal or external location make a difference? I've seen that hard drives should be 0-1, CD-ROM CD-ROM: see compact disc. CD-ROM in full compact disc read-only memory Type of computer storage medium that is read optically (e.g., by a laser). 2, and so forth. A: The assignment of SCSI IDs to devices on the bus has nothing to do with the physical location of the device on the SCSI chain. Some operating systems want hard drives to be at TD 00 or 01 and CDs to be at ID 02, etc., but whether they are internal or external is irrelevant. In most cases, regardless if it is a wide or narrow bus, the host adapter is assigned to ID 07, as it has the highest priority. The order of priority for SCSI IDs is 07, 06, 05, 04, 03, 02, 01,00, 15, 14,..., 08. Q: How much overhead does the SCSI protocol require to execute a single SCSI I/O (Input/Output) The transfer of data between the CPU and a peripheral device. Every transfer is an output from one device and an input to another. See PC input/output. I/O - Input/Output ? I have read that it is 320K per every 1MB or 32 percent. Is this correct? A: The overhead is related to the packet size and the application. 2K block size 30 percent is about right. However, if you have 2K block size, most operating systems cannot handle the number of I/Os needed to load the SCSI bus. You would need at least 15 drives on the bus because the head positioning time is the dominant factor. Head positioning is two to eight milliseconds for the current disk drives. Q: Do both single ended and differential SCSI peripherals use the 68 pin connectors and cables? Is it dangerous, electrically, to allow two separate electrical interphases to plug in using the same cable? A: Yes. The number of pins in the connector depends on the width of the bus, not on whether it is single-ended or differential. If the interfaces are correctly designed, plugging a single-ended device into a differential bus (or vice versa VICE VERSA. On the contrary; on opposite sides. ) will not damage anything. That is what the DIFFSENSE line is for. The HVD differential bus and the narrow bus (8-bit) will disappear, as they are both rendered obsolete in the SPI-3 document of SCSI-3. |
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