Question: I finally crashed my old HDD (backup was made from the first SMART notice). But now the problems is what drive to buy?

I had a 500 GB SATA/300 5400 RPM device with 8 MB cache. 

My machine is a laptop: Intel Code 2 Duo T4500, 4 GB RAM (DDR2), 64-bit machine (tell me what other specificatons could be relevant as I do not remember them now and have to look them up).

I have 2 TB of external storage, so storage is not important. I want speed improvement though.

1. What drive should I purchase (skip if the question is too general)?
2. Should I consider an SSD even if I only have SATA II (SATA 300) Interface?
3. If i should stay with HDD, would I benefit from buying a 7200 RPM drive? What other parameters are important for speed gains?

Thanks in advnce :)

Answer: 
I haven't worn out my SSD yet (OCS Vertex 4 128Gb), but there is caution: SSD's memory cells can perform only limited number of writes. Therefore, you're advised to minimize the number of writes, on Linux, you should follow [these](https://wiki.archlinux.org/index.php/Solid_State_Drives) instructions. Basically, you should tell the OS not to use swapping very actively (should it really need swapping, it's fast, but OS shouldn't swap when it's not critical).

Also, it's good if the SDD/OS/driver supports TRIM command.

Notice that SDDs are random-access devices, unlike HDDs. OS may waste time packing adjacent IO requests, so on Linux, for example, you should move to `noop` IO scheduler. Also, google and make sure the SSD you want to buy provides good SMART test data (mine is not very informative).

Don't hesitate, HDD is one of the slowest devices in the system, with SSD you'll see the difference even with SATA 2. If you need more space, you may guy hybrid SSD/HDD.

P.S. Moreover, SSDs are quite complex devices, so firmware does matter.
Although this is a purchasing recommendation and not really appropriate for Superuser (so don't be surprised if this post is closed)

There is no problem using an SSD with a SATA interface and it will give you a massive increase in speed over a standard hard disk. Depending on the age of your computer your sata disk will support a speed of 150 - 600 MB's per second. An SSD will give you speeds of (very roughly) 200 to 500MB's per second, compared to (again, very roughly) 20-70 MB for a typical laptop drive - you should expect a "raw speed" increase of about 3 fold using an SSD - but thats not the whole story. SSD's also have a MUCH lower latency, and this makes everything feel more responsive.

I've deliberately stayed clear from recommending a particular brand of SSD but depending on what you are doing you probably want a 128 or 256 Gig SSD to complement your external drive. Just be aware that SSD's are as likely to fail as hard drives, only, when they do they are MUCH less likely to give any warning then hard drives, so make sure you back up anything important on it very regularly.

If you do stay with hard drives, 7200 RPM drives are faster then 5400 RPM drives, primarily because (I believe) of their lower latency. If you are going the hard drive root, you might want to explore a hybrid drive - these are typically 5400 rpm drives with a smallish SSD cache which can boost your performance quite dramatically for many desktop-type workloads (moreso then a 7200 RPM drive) - particularly if you tend to read the same data sets frequently. They are much cheaper then pure SSD drives.