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Why do SCSI drives come in such different sizes than IDE drives?

Part of it is tradition and the fact that the drives spin so fast that the arial density must be lower to avoid errors. That is there is less information on a platter in a scsi drive...
 
Generally the sizes of SCSI drives are lower because the densities are low to enable faster seek times. As a simplifcation, if your tracks are wide and far apart you can have less accuracy on the read head that's moving back and forth. This allows you to move the head faster and still hit on target - because your target track is bigger. But this reduces the density of the drives, so you have a lot less storage space.

On a similar note, by having a wider track pitch (pitch = width + spacing), you can spin the disk faster and still have low error counts. If the density is high, then you need to implement some method of keeping vibrations down - or compensating for them - in order to find the track that you want. So the densities that are acheiveable on a 7200rpm IDE drive like the Maxtor 740X wouldn't work at all on a 15,000rpm SCSI drive like the Seagate X15.

The two drive interfaces target different markets. SCSI is aimed at servers where data reliability, seek times, and overall performance are valued more highly than cost. IDE is targetted at the home market and some multimedia markets where storage space and cost are valued over data reliability and performance. Data reliability and seek rates are hard to achieve with high density.

Edit: fixed a couple of typos and elaborated on my second paragraph and then added a third one.

And, although it's confusing to a see a reply to a post that's further down, thanks for the compliment, Hanpan. 🙂
 


<< Generally the densities of SCSI drives are lower because the densities are low to enable faster seek times. As a simplifcation, if your tracks are wider apart you can have less accuracy on the read head that's moving back and forth. This allows you to move the head faster and still hit on target - because your target track is bigger. But this reduces the density of the drives, so you have a lot less storage space.

On a similar note, by having a wider track pitch (pitch = width + spacing), you can spin the disk faster and still have low error counts. If the bensity is high, then you need to implement some method of keeping vibrations down - or compensating for them - in order to find the track that you want. >>



That is exactly what i was trying to say.

Thanks pm for comming and showing the way.
 
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