Here is a good question...

[Tab]

Serial ATA is obiviously serial and PCI-Express is a serial interface. Why is the everything serial all the sudden? If I am correct serial is the transfer of one bit after another and Parallel is a group of bits at once. So why the change?

 

[joecool]

yes you are correct (you're a diamond member and you had to ask?!)

reasons:

1) serial can run REALLY fast (we just finished a 10gb/s product at work)
2) interface is smaller (1 line for data plus a few control vs. 16/32/64) and so simplifies many parts of the design - chips, boards, connectors, etc.

used to be serial was slow and so to speed up an interface it was easier to add more lines ... now serial is fast and cheap, and with parallel ramping the speed gets harder and harder to try and keep so many lines in sync.

hope this helps,

joe

 

[oneshot47]

Same thing happened when usb [essentially] replaced parallel ports.

 

[Cerb]

For transferring things over several feet, it has, in the past, been difficult to speed the interfaces up. Or often times, easy to do, but very costly. Over the past several years, many technological barriers have been broken. Not really broken, but what were once insanely expensive ways to get things done have now come down (and been tweaked along the way, else it'd still be expensive) to where anybody can manufacture speedy gadgets--or at leats contract somebody else to.

One of the problems with any design for transferring data is that you have to have X lines at the same width (or at least within a certain tolerance for the speed you need). Not to mention there's some magic in EMI that can cause parallel lines at similar fequencies to amplify the noise coming from them (at least as far as the recieving end is concerned).
So cutting down the path's width, you can design things easier, having to deal only with 16 or fewer traces at a time, typically. Also, you only have to make the controller use these, which can bring its size and complexity down. Using LVD adds more, but also allows speed benefits that are worth it (see SCSI and HT).