Reply 20 of 43, by Jo22
Okay, back on topic.. Speaking about SCSI and Windows..
SCSI had a predecessor to Native Command Queuing (NCQ), called Tagged Command Queuing (TCQ).
Both are important in a multitasking environment, in which multiple files are being used simultaneously.
Let's imagine a lift, an elevator in a small building.
Without NCQ, the order in which a floor is being reached is chaotic (depending on button requests each time): 4-1-3-1-2
With NCQ, the lift moves in a row, so all passengers get to their floor ASAP: 4-3-2-1
That's one of the reasons as to why SCSI or SASI is being used in professional fields or on Unix.
While PATA/IDE HDDs may support these features, it's not guaranteed that OS, the IDE drivers or the IDE controller support such things.
In the SCSI world, however, these features are very old, so there's a chance classic software can make use of it (through SCSI).
If you're on plain DOS, that's not needed, of course.
Rather contrary, NCQ/TCQ can reduce linear read/write performance due to their jumpy behavior.
In a humble DOS/16-Bit Windows environment, an IDE caching controller may indirectly solve the same issues as NCQ/TCQ by combining/buffering I/O requests.
That's one of the reasons as to why SmartDrive and the 32-Bit File Access (HDD cache) can improve smoothness noticeable.
If you can, please consider experimenting with SCSI a bit. There are SCSI emulators by now.
You won't regret it once you play with Unix, OS/2 or Windows NT/9x.
Edit: Or in other words, NCQ/TCQ make the HDD multi-tasking capable.
So it makes sense that they're ideal, if not required, for multitasking systems.
Otherwise, an HDD can only handle one request at a time.
In relation to thousands of files, this gives an idea how important they are.
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In what to one race is no time at all, another race can rise and fall..." - The Minstrel
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