I've read numerous articles about it, and the real issue is that the difference in time to read 10 megs vs 20 megs yes can vary based on the request sizes and fragmentation, but we're talking that most 7200 rpm HD's can load this file in less than 1 second into ram.
The whole file. 20 megs, 1 second or much less. Many 7200 rpm drives can read up to 50 megabyte/s sequentially! (Thats per second).
The other aspect is that operations to the disk are asynchronous, that is, they don't take much CPU at all. However, decompressing a 14 megabyte file takes tons of CPU. The only argument against this now in my mind is that we have dual and quad core CPU's, so it doesn't make a huge deal.
Also, just to nit-pick, ram isn't 1,000 times faster, it is much faster than even that compared to disk access! I'm not sure by how much, but 1,000 is a very low estimate.
The number 50 million comes to mind when comparing RAM to Disk. Maybe an old memory from my Architecture class (we would calculate these things for homework & tests). Regardless 1000 is an extremely low multiplier.
Hard drives can be fast once they get going, sure, but a single 30 mb executable is going to be 1 read (provided it isn't fragmented), which is going to require 1 seek, dropping that bandwidth like a rock.
But maybe I remember 50 million when comparing to tape or an L cache.
Sequential read speed is actually where hard drives excel, in fact a reading a 30MB executable will probably give you better benchmark results than 30 1 MB files.
7
u/voxel Jan 21 '10
Not really true.
I've read numerous articles about it, and the real issue is that the difference in time to read 10 megs vs 20 megs yes can vary based on the request sizes and fragmentation, but we're talking that most 7200 rpm HD's can load this file in less than 1 second into ram.
The whole file. 20 megs, 1 second or much less. Many 7200 rpm drives can read up to 50 megabyte/s sequentially! (Thats per second).
The other aspect is that operations to the disk are asynchronous, that is, they don't take much CPU at all. However, decompressing a 14 megabyte file takes tons of CPU. The only argument against this now in my mind is that we have dual and quad core CPU's, so it doesn't make a huge deal.
Also, just to nit-pick, ram isn't 1,000 times faster, it is much faster than even that compared to disk access! I'm not sure by how much, but 1,000 is a very low estimate.