stupid Qn. But why no 5.25" HDDs?

Roland0

Roland0

Roland0

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Hey,

As per title, why did the 5.25" format for HDDs die? Imagine the capacity they could have, 4Tb or so i could imagine. :)
 
Smaller hard drive = reduced seek times and faster transfer rates. Thats why the current Velociraptors are 2.5".
Plus, the 5.25" Quantum Bigfoot (Yes, I had a 1Gb one) were all faulty. Mine luckily gave up the ghost 11 months and 2 weeks into the warranty of my brand spanking new Pentium 200MMX (Bought from Special Reserve!)
 
Faster transfer rates on bigger drives due to greater diameter => faster actual speed at outside of 5.25" vs 3.5". Seek times however make sense. And rotational speeds might not have been as fast (i.e. 5400rpm instead of 7200rpm), I don't know if they'd be slower though.
 
PhillyDee said:
Smaller hard drive = reduced seek times and faster transfer rates. Thats why the current Velociraptors are 2.5".
Plus, the 5.25" Quantum Bigfoot (Yes, I had a 1Gb one) were all faulty. Mine luckily gave up the ghost 11 months and 2 weeks into the warranty of my brand spanking new Pentium 200MMX (Bought from Special Reserve!)
Click to expand...

you just brought back soooo much memories for me :)
 
Heat, theres no real inherent seek time increase, you could add a second head if you wanted for the outside layer, so both heads would only be moving the same amount of distance, most of the seek time is in the starting and stopping rather than the movement phase anyway.

The problem is you just can't have a 10kprm drive thats 5" in diameter, the outside edge is moving a lot further than the inside track, its essentially moving a heck of a lot faster and the bigger the platter the greater the speed on the outside.

Basically the outside would be moving, accelerating and slowing down enough to introduce more torsion and you end up with a hugely friction inducing over heating and shattering platters. We just don't have the materials available to be light and strong enough that can store enough data to move that fast without a huge amount of failures.

THeres entirely no reason you can't have a 2krpm 5" drive with ridiculous capacity, but we don't really need those drives. They'd be far slower, use more energy most likely with a great weight per platter and, well most people just don't need sizes that big, and those who do, servers that store lots of data, prefer multiple smaller drives so they can run in multiple raid configs for redundancy.
 
Thanks for the good explanation, I was wondering about this when I saw the question. Seek times certainly aren't much of an issue, no 2.5" disk has disk really has notably lower access times than a 3.5" one (the VR gained just over 1ms as I recall which can be attributed elsewhere).
 
5.25" platters can store roughly twice as much as the 3.5" platters, but made from the same materials they are harder to manufacture with a uniform flatness, less rigid so they suffer more from shock and vibration (which affects reliability) and heavier so they take more power and time to spin up.

Basically it's cheaper, easier, faster and more reliable to use two 3.5" drives.
 
AbsenceJam said:
no 2.5" disk has disk really has notably lower access times than a 3.5" one
Click to expand...

We tend to use 10K 2.5" drives these days since we can fit more disks in a server, whilst losing only a fraction of performance over a 15K 3.5" (the average seek time is almost identical for the most part). The 15K 2.5" drives are even faster than the 15K 3.5" drives.
 
If my maths is right, the outside edge of a 5.25" platter at 7200rpm would be travelling at 225mph.

2 * pi *5.25 = 32.991 inches per revolution

32.991 * 7200 = 237535.2 inches per minute

237535.2 * 60 = 14252112 inches per hour

14252112/36 = 395892 yards per hour

395892 / 1760 = 224.938 mph.

Too fast, considering the tolerances required in a HDD.
 
Speed (Of the outer edge) = (pi x Diameter x RPM)/1000
(3.14159 x 133.25 x 7200) / 1000

= 3014.041 M/Min

= 122 Mph. . . . (Google conversion)

I get half yours . . . . ;) You have doubled the diameter.

Anyway, the platter size is less. 5.25" is the form factor not the size of platter.
 
Zarf said:
5.25" platters can store roughly twice as much as the 3.5" platters, but made from the same materials they are harder to manufacture with a uniform flatness, less rigid so they suffer more from shock and vibration (which affects reliability) and heavier so they take more power and time to spin up.

Basically it's cheaper, easier, faster and more reliable to use two 3.5" drives.
Click to expand...

The platters were made of metal back then i beleive they are made of glass now.
 
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