IDE's lie. For instance a 20GB HDD is actually 18.8GB. personally i think it's because IDE is used by the great unwashed so they round them up/down where appropriate but as SCSI is generally used by more computer literate people who want to know the true size. Thats my opinion anyway.
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That's what someone else told me yesterday. Couldn't the formatting affect the amount of space though, like with a DD disk being 1MB, when formatted it is only 880k? I'm not sure how the formatted capacity of SCSI HDs differs from that of IDE/SATA HDs.
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I don't think it does. IMO It's just that the figure given on SCSI is post formatting and the figure for IDE is Pre formatting.
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It's actually how data sizes are interpreted. We all know that 1MB = 1024KB and 1GB = 1024MB. But HD manufacturers instead decide to state HD sizes based on 1MB = 1000KB and 1GB = 1000MB.

This makes the HDs look slightly bigger, but obviously when you format them the computer is using the proper data sizes of 1GB = 1024MB to display capacity, so when you compare the two it always looks like you have lost some space on the drive once it has been formatted.

So if you convert it. A 20GB HD is actually really 19.53GB unformatted.

Plus you will always lose some HD space from the true total as well once formatted because the structure has to keep some of the space back for housekeeping and indexing needs.

This is due to the faster spin rates of most SCSI drives compared to IDE and SATA. Due to 15,000RPG drives spinning at least twice that of standard IDE/SATA 7,200RPG drives the data rate and seek times are increased, but capacity suffers.

If you also look at the fastest IDE drives they also come in these lower odd capacities too. Have a look at the Western Digital Raptor range to see this.
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