Why is a hard disk 3.5 Inch???

[Conradl]

I am sure that there is a rational answer to the question; I just don't know what it is! Why is a hard drive 3.5 inch??

Old hard drives used to be 5 1/4 quarter inch. As technology improved they were able to make disks smaller. At the same time Floppy disks were also reduced in size, so it made sense to create a 3.5 inch standard. Then CDs were released on a 5 1/4 inch standard, but HDDs remained at 3.5 inch??

I can think of lots of reasons why a 5 1/4 inch disk would be better:

1. Higher capacity, you have more platter space and therefore higher capacity
2. Higher performance, your outermost track is longer than a 3.5 inch disk, and therefore faster (thanks to angular velocity the outer portion of the disk is faster). If capacity were not an issue then you could create the same capacity disk; but keep a longer track length and increase performance.
3. Higher performance due to more space. If manufacturers had more space to work with; then I assume that disks would be faster. Think of how fast a tape drive is; largely because they don't have to cram everything into a tiny 3.5 inch shell.

So why is a disk 3.5 inch???

 

[orin76]

So why is a disk 3.5 inch???

I'm guessing it's because smaller is better in the world of computing and the 3.5 inch was an established standard from the 1.44 MB stiffy disk era. As far as CD drive sizes are concerned, the CD/DVD media is the limiting factor. If mini disks had taken off, we'd probably all have 2.5 inch DVD drives in our PCs.

 

[chickenbeef]

I think if the drives were bigger it will also amount to more heat being generated and even less airflow in the case

 

[Chevron]

I was thinking the same thing but with regards to ssds. I'll wait for 3.5inch ssds.

 

[dequadin]

I can think of lots of reasons why a 5 1/4 inch disk would be better:
1. Higher capacity, you have more platter space and therefore higher capacity

Yes

2. Higher performance, your outermost track is longer than a 3.5 inch disk, and therefore faster (thanks to angular velocity the outer portion of the disk is faster). If capacity were not an issue then you could create the same capacity disk; but keep a longer track length and increase performance.

Not necessarily true.

Because it has a greater radius and a greater velocity it's angular momentum will be a lot more since it's directly proportional to both. This will cause major problems for the control system moving the head of the drive. It will have to exert a greater force to stop the head and it will probably have to start slowing the head down sooner. This will require a bigger more expensive motor and more power consumption.

3. Higher performance due to more space. If manufacturers had more space to work with; then I assume that disks would be faster. Think of how fast a tape drive is; largely because they don't have to cram everything into a tiny 3.5 inch shell.

Disk space is definitly not proportional to performance. Even with a higher disk space the same compression and error recovery algorithms would be applied. The main reason a tape is faster than a HDD is because of fragmentation. HDD's become fragmented over time whereas tapes don't because of the way they are used. i.e. tapes are used for backups. If you had to have a severly fragmented file on a tape and it had to fwd and rwd the whole time just to read the file.

So why is a disk 3.5 inch???

Because some guy with big glases who lives in his mother's basement (sorry "Command Centre") proved they are better!

 

[LazyLion]

Quantum Bigfoot...

Those were some big ass drives.

 

[chris2.0]

Was just going to say the same - only saw one of them in my entire PC career tho...

 

[XysteR]

Because it has a greater radius and a greater velocity it's angular momentum will be a lot more since it's directly proportional to both. This will cause major problems for the control system moving the head of the drive. It will have to exert a greater force to stop the head and it will probably have to start slowing the head down sooner. This will require a bigger more expensive motor and more power consumption.

Yeah i think thats the main reason. Have you ever seen on mythbusters when they spin a CD (5 1/4 inch) at high revs and it begins to warp tremendously and eventually it actually explodes and pieces fly off in many directions

 

[remybfg10k]

I am sure that there is a rational answer to the question; I just don't know what it is! Why is a hard drive 3.5 inch??

Old hard drives used to be 5 1/4 quarter inch. As technology improved they were able to make disks smaller. At the same time Floppy disks were also reduced in size, so it made sense to create a 3.5 inch standard. Then CDs were released on a 5 1/4 inch standard, but HDDs remained at 3.5 inch??

I can think of lots of reasons why a 5 1/4 inch disk would be better:

1. Higher capacity, you have more platter space and therefore higher capacity
2. Higher performance, your outermost track is longer than a 3.5 inch disk, and therefore faster (thanks to angular velocity the outer portion of the disk is faster). If capacity were not an issue then you could create the same capacity disk; but keep a longer track length and increase performance.
3. Higher performance due to more space. If manufacturers had more space to work with; then I assume that disks would be faster. Think of how fast a tape drive is; largely because they don't have to cram everything into a tiny 3.5 inch shell.

So why is a disk 3.5 inch???

Cause the water is cold

 

[elmorya]

worked for Burroughs (States company) in the mid seventies - our disk were about 17" in diameter and weighed about 20KG!

 

[krycor]

lol @remybfg10k