Friday, February 8, 2013


How do they work

HDD uses a writer/reader attached to a mechanical arm which moves very fast to the right location of the disk to read or write data while the platter ( where the data is stored ) spins also very fast, normally 7200  revolutions per minute. The technology in HDDs is magnetism.

SSD uses the NAND flash technology ( there is no mechanical movement involved ) which takes less time for gathering data than HDD that has to look everywhere on the disk and find the data blocks ( they may also be spread out on the disk which makes the search even slower ). SSD is just a bigger and more advanced version of a memory stick. There is a embedded processor inside SSD and it controls the data manipulation ( caching, cleaning, storing, retrieving ).


The comparison is made on avarage.

AttributeSSD - Solid State DriveHDD - Hard Drive Disk
Cost per GB$0.70$0.1
Size - both vary
Small and lightweight

A bit heavier
Transfer speed100 to 600 MB/s50 to 140 MB/s
Reading latencyVery low because it happens in a flashHas to find the data segment every time from different location
Start-upFew millisecondsSeveral seconds
TemperatureTolerates higher temperatures. Some models even come with heat sinks.Can get very hot in hot places or under heavy workload and may need cooling ( over 35°C / 95°F shortens lifespan ).
ReliablityNo mechanical parts. Number of times data can be erased varies between models and brands. DRAM has no "number of times" limitation. Not affected by vibration or shock.Can fail mechanically. Possibility of data "tear". Almost no degration from workload. Strong magnetic surge can damage the stored data. Needs shock and vibration protection.
CapacityUp to 2 TB. Most common 64-256 GBUp to 4 TB. Most common 500 GB - 1 TB
NoiseMay occur electric noise, but mainly silent.Some but little noise.

What HDD looks like inside

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