DMA/66 and SCSI

DMA/66 considerations

If you are going to be using the drive on a DMA/66 capable system, then you will want to make sure that your drives and your system both support DMA/66. You can check with the manufacturer of your hard disk and motherboard to find out if they have DMA/66 support, or if there are any special requirements to enable DMA/66. Most of the newest motherboards directly support DMA/66, but on some of the older BX boards you might have an onboard HighPoint DMA/66 controller and two special DMA/66 headers. If your motherboard doesn't have DMA/66 support, you can always get a controller card.

In all cases, you will need to use a special 80pin IDE ribbon for DMA/66. Standard cables have 40 pins and 40 conductors, the DMA/66 cables still have the same 40 pins, but they have 40 more conductors that are used for grounding purposes to prevent signal crosstalk, which is term for when a signal being transmitted on one wire jumps into another that is close to it. This causes signal degradation and data loss.

SCSI Drives

SCSI is a very old technology, older than ATA IDE. IDE and SCSI are actually very closely related (A SCSI drive technically is an IDE type drive), but they are treated by the system in very different ways. SCSI has some very important advantages over IDE, and these advantages make them especially suited for roles in a server system, or a RAID (Redundant Array of Inexpensive Disks), where fast access to loads of data is mission critical.

Speed used to be SCSI's major selling point, but with the recent release of the UDMA/66 IDE drives, SCSI isn't such a speed king anymore. However, it still offers the flexibility of allowing more devices and SCSI devices also use fewer system resources than a comparable number of IDE devices would require. It should also be noted that unless your motherboard has a SCSI controller built in, you will be required to purchase and install a SCSI controller card for your SCSI devices.

No masters or slaves here

SCSI Drives are jumpered very differently from IDE type drives, and it can be a lot tougher to get multiple SCSI devices jumpered correctly. However, if you know a little binary, the job is made a lot easier since the SCSI ID setting is based on a binary numbering system.

The first thing you need to remember is that, by default, the SCSI host (your controller card) is normally set as SCSI ID 7. This ID can be changed, but I recommend that you leave the HOST as ID 7. As for the devices, there is no real preferred pecking order for setting SCSI ID's, but I myself prefer to keep them in a logical progression. Most hard disks ship preset as SCSI ID 6. Keep the boot drive as ID 6, then and then progress downward, making the next drive ID 5, and then 4, and so on and so forth.

Setting the SCSI ID

SCSI Drives will have 3 jumpers for setting ID, usually numbered 0,1,and 2. This is where things start to get a little confusing because each pin has a binary value to it. On most drives, pin numbers 2, 1, and 0 will correspond to the binary values 4, 2, and 1.

Remember that most drives ship as SCSI ID 6, so by default, pin #'s 3 and 2 will be jumpered. Since pin 3 has a binary value of 4, and pin 2 has a binary value of 2, the total binary value is 6 for ID setting 6. If you wanted to jumper the drive as ID 5, then you would jumper pins 3 and 1, for a binary total of 4+1=5.

Please keep in mind that the arrangement of the pins is totally dependant on the manufacturer of the drive, so be sure to check with the drive's instructions. Once the drive is jumpered correctly, the SCSI BIOS will take over from there, detecting the drives and assigning each a drive letter.

Unless you are a fairly experienced user, or foresee yourself needing more than 4 IDE devices in a system (and have a power supply to support them), I still recommend IDE as the best choice for the home user simply due to its ease of use and price. IDE is supported by virtually every motherboard on the market, as compared to SCSI which either requires a separate controller card, or a board with SCSI built-in, and these are typically more expensive than standard motherboards. So unless you really need SCSI, go IDE.