A co-blogger on PlanetEDS (Charlie Bess) posed this question after I commented on his recent blog entry about whether Ready Boost was making any noticable difference. I think it does, but that wasn’t what the comment was about. The question was, since USB keys have a limited R/W cycle lifespan, how long will the USB key last given Vista is using it as a cache?
Ok, well after a (very) limited amount of research, it turns out there are two types of memory used in Flash devices, (Nand/NOR) but the thing that dictates the Keys lifespan is its Multi Level Capacity.
Both types come as Single Layer and Mult-Layer, but whilst Multi layer has a slight price advantage for larger capacities its lifespan appears to be significantly reduced to around 10,000 cycles. Single Layer on the other hand, doesn’t suffer from this limitation, and can survive for 100,000 cycles or more. Luckily it appears most USB keys are SL devices.
Given Key prices are pretty cheap, i’ll assume we’re using 8GB keys for Ready boost.
Supposing we’ll split our device into 1K blocks, for our 8GB key we’ll have 8,192,000 available 1k chunks. Take the number of R/W Cycles an SL device allows us, this gives us 8192000*100000 = 819200000000 R/W’s per K. ( this is assuming that devices do RW balancing and do write accross the entire device) and you’re going to write 1MB per second , this gives 819200000000/1000 = 819,200,000 or 13653333 RW minutes or 227555 hours of use.
Unless my Windows calculator doesn’t work with big numbers (hey, I have to blame something 😉 thats almost 26 years of continuous use.
Conclusion : by they time it wears out, I’ll be able to nip down to PC World in my fusion powered hover-car, and buy whole case of 1000 peta-byte keys to replace it, for £1.52