why are internal hard drives faster than external?

USB 2 is a slower transfer method than internal drive methods. USB 2 has a maximum transfer rate of 480 Mbps (60 MB/s), PATA has a maximum transfer rate of 100 MB/s, SATA I has a maximum transfer rate of 150MB/s, & SATA II has a maximum transfer rate of 300MB/s. The best way to determine the speed of your notebook's hard drive is to download and run HDTune or a similar hard drive benchmarking program.

RPM would help in read/write data.

IDE speed? Meaning hard drive controller in general? That was what Djembe mentioned with PATA and SATA references.

cheers ...

Yes, revolutions per minute matter for read/write speed, as Q said. However, the limiter on the maximum read/write speed of the drive is the controller/type of interface.

Regarding IDE modes, you can change them for your drive, but doing so is probably only going to lower your performance. Windows typically sets up the fastest available IDE mode for any drive that it can handle.

just for note, the external SATA (eSATA) format is gaining popularity, and that allows you to use an external at full SATA speeds, so if you need speed for an external drive then you would want to look for eSATA (presuming you have an eSATA port)

The bus is essentially the channel the data flows through to and from your hard drive. You can think of it as the bottleneck of a bottle. For the liquid to get from the inside of the bottle to the outside world it has to travel through the bottleneck (which tends to limit the flow of liquid). In the case of (modern) internal hard drives, the bus is SATA. The bottleneck is the bandwidth of SATA. For external hard its a variety of interfaces such as USB 2.0, 1394 (firewire), ethernet, wireless, bluetooth, esata, etc. The bottleneck in each one of these cases is essentially the bandwidth of the interface its connected to. None of these external interfaces are as fast as SATA (except for eSata which uses the SATA bus).

The reason rpms (on mechanical hard drives) are important is because the datarate of the harddrive have not saturated (i.e used up) the bandwidth of SATA (either 150 MB/s or 300 MB/s). So, in that bottle analogy, its like we are pouring liquid out of a glass instead of a bottle; water's flow out of the glass is not limited at all by the opening (top/rim) of the glass. So RPM's allow us to get faster and faster until at some point, our glass turns into a bottle (with a bottleneck). Essentially though, mechanical hard drives will never get fast enough to saturate SATA 2 as we are moving on to SSD's. SSD's are pushing close to the 3 GB/s boundary already. But once they get closer, we'll just make an even faster SATA specification (or a different specification if this becomes infeasible).

Regardless, nothing I am saying now will be that important in the future. A version of USB 3.0 has already been certified which supports 5 GB/s (only Linux supports USB 3 now even though afaik there are no USB3 supported motherboards). A newer version of firewire (not sure of the release) will support 6.4 GB/s. There is a newer version of SATA which supports 6 GB/s. As you can see, the newer firewire will be faster than the newer SATA. However, unless a hard drive is made with native firewire support (which won't happen) you will always have "bridging inefficiency" translating the meaning of the firewire ports to the SATA interface. Essentially, internal SATA will still be faster than a translated SATA on a faster bus. However, the new firewire would probably be a dagger into the eSATA market.

Just a note with at least current USB technology it's theoretical bandwidth and actual are very different. USB 2.0 is half theoretical because of "overhead" and how it works. USB 2.0 beats the current "firewire" in theory but not actual.

The others did explain well. External is simply not as fast other than say eSATA, bandwidth.

Just wanted to clarify one small thing in zzpulp's excellent overview: the new SATA, USB, & Firewire (IEEE 1394) standards are measuring themselves in gigabits per second, not gigabytes per second (the terminology in which most data is saved). One byte is 8 bits, so the actual thoroughput is closer to 600 MB/s. This is still much faster than even current SSDs are now, however they will likely bridge that gap within the next couple years.

Yes, but you did open a can of worms on that. It is called "areal density". So in general and a very general sense your 120GB @7200 is likely slower/bandwidth than your 320GB @5400? Unless you want to get further into I will stop here.

^^ Powerpack - you are a tease!

Moved to Hardware General

cheers ...

Its impossible to just generalize. It would depend on the sizes of the hard drives.

And yes Djembe, I think every capital B in my last post was supposed to be a lowercase b.

I can guarantee any current internal 5400 HDD is faster than any USB 2.0 HDD 7200/10,000 in sustained reads or writes but not seek time/random access. So depending on what you are doing which will perform better could vary.