[OS X TeX] New Laptop...

Ralph Martin Ralph.Martin at cs.cardiff.ac.uk
Fri Jun 24 15:49:21 EDT 2011

On 24 Jun 2011, at 8:07:38PM, Peter Dyballa wrote:
> Am 24.06.2011 um 17:39 schrieb Ralph Martin:
>> You are way, way off beam. The Intel X25-M, as an example, has a mean time before failure of 1.2 million hours (more than 100 years).
> MTBF is not the question (it's good enough, OK for a server). The number of charge changes of the storage cells is limited (different to that of real hard disks). You can achieve that limited number of changes in a few hours and store the zombie disk in your laptop for another million hours... still an ultra-fast read-only device! 

Nonsense, I am afraid. Current SSDs allow 1-5 million write cycles. Combined with wear levelling (to ensure all parts of the SSD get written to evenly), this still translates to  more than enough life:

If we assume perfect wear leveling (over optimistic, of course), we need to fill the disk 1 million times (conservative) to get to the write endurance limit.
1 million writes times 64GB (a small SSD) divided by 100MB/sec (realistic transfer rate) gives the endurance limited life in seconds, IF we assume the disk spends its entire life writing, 24 hours a day, nonstop (completely unrealistic, of course).
Work it out. It comes to 20 years. 
The 1.2 million hours figure takes into account the limited write cycle count of SSDs under more typical usage.

Best wishes

Prof Ralph Martin                          Phone: +44(0)29 2087 5536
Computer Science & Informatics             Fax:   +44(0)29 2087 4598
Cardiff University                   Email: mailto:ralph at cs.cf.ac.uk
5 The Parade, Roath                  WWW:  http://ralph.cs.cf.ac.uk/
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