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johnfoster

SSDs - the sky is falling! the sky is falling!

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SSDs are rapidly falling in price. most drives are half the price they were six month ago. and this last posting (august 8, 2012) makes them even cheaper. and very tempting even with the shortcomings that go with a rebate (limit one per customer, we'll take forever to pay you, hopefully you will forget to send it in. requests postmarked on Monday are disqualified unless the stamp is upside down. additional rules are written on a rock in Nebraska found in a corn field about to be harvested so mind the combines and tractors.) if you don't buy a SSD today you will sometime in the next six months.

the advantages of SSDs cannot be understated. having one, even a "slow" one, will make the thing you put it in seem like a new thing. this is especially true for older hardware that you were about to write off because it was so "slow". boot, launch and generally use will seem snappy compared to a spinning hard drive. it won't actually speed up the processor but it turns out that lots of the processor was bottlenecked by factors caused by the disk. the biggest of those is the RAM cache.

the difference between a spinning disk and a solid state drive is there are no "head seeks" on the SSD. each time the head has to move to read more data it takes time to change tracks. depending on where the data is on the drive that track seek could take as long as 40 milliseconds. although the actual time depends on factors like how old the drive is, the size of the drive platters and the sequence of the data. obviously a track that is right next to another track won't take that long to arrive on. all drive track seeks are listed as average times for this reason. but an SSD doesn't have physical tracks so there is ZERO apparent seek time when reading data. so there isn't an accumulation of seek, seek, seek that eventually adds up to slow. do the math. if the average seek was 10 milliseconds and there were 50 seeks during the read that adds up to 500 milliseconds which seems small until you look up how long a millisecond is. for the click impaired that is half a second.

while milliseconds add up quickly there isn't much more that physical hard drive makers can do to get the seek time down. this is mostly do to the cost reduction for making the hardware. but there's also limit to what magnets and coils can do. they've reached that speed. although I blame marketing. once the millisecond barrier is crossed the number changes to a big nanosecond like 800 or 980. marketing HATES big numbers when it comes to selling speed.

what's telling about SSDs is that Apple (and other vendors following this lead) has replaced spinning disks in almost all offerings. the two Air and the Retina MacBooks have no spinning disk options. it's all solid state. the Mini and MacBook Pro have a SSDs as a BTO option. and the Mac Pro… whatever, that thing needs to be rethought.

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