*Updated* I had my math wrong and I’m correcting and taking back what I originally said.
The issue came up the other day, while I was reading the newspaper for an advertisement for SATA Hard Drive. It stated that since it ran at 150 MB/s that it was faster than ATA 133, which has speeds of you guessed it, 133 MB/s. The first impressions would that it wasn’t accurate, but it actually is.
The Math
Serial transfer uses 10 bits, instead of the parallel 8 bits. It uses a start and stop bit for error checking and handling.
The actual speed of SATA 1 is 1.5 Gb/s divided by 10 is 150 MB/s.
Correction:
The 20% should be taken from the 1500MB and not the 150 MB.1500 – (1500*.2) = 1200Mb
1200 / 8 = 150 MB
The formula would then be:
MaxMb – (MaxMb*.2) = ActualMb
ActualMb / 8 = ActualMB
Or just:
MaxMb / 10 = ActualMB
Which is why I came up with my crazy ass conspiracy theory. It seems that in my arrogance, I didn’t see that the 10 was including the overhead and therefore the actual speeds should be lower. I must of came across the first formula earlier in my research but needing an easier way decided the second was faster. Using the second formula I forgot that it was including the overhead, and decided to take out the 20% in that. Goes to prove that the larger formulas are better for somewhat confused individuals.
Serial ATA Benefits
The added benefits of Serial ATA outweigh the overhead. The max speed for PATA is probably 200 MB/s and that is really pushing it. PATA also has the 18 inches length limit, you can run SATA up to a meter or more. SATA only allows for one connector, but since it simplifies the board circuits, you can have as many as the bus will allow. I’m already seeing boards with 4 to 6 SATA connectors.
Phasing Out PATA
As soon as DVD, CD-ROM, and other drives start using the SATA connector, it will eventually mean the end of the PATA life. PATA will still be around for another 3 to 4 years, but like PCI Express replacing AGP, you will eventually find motherboards without PATA or with only 1 primary slot. The major problem with not having a PATA slot is that Windows XP has problems unless it finds and can install on the PATA drive. The problem may deal more with the special drivers and not with Windows XP, but the conflict should eventually be solved.
Floppy drives are no longer mandatory and if you really need to, you can write MS-DOS to a CD-ROM and have all of your disk utilities on there. It is what I have and it isn’t all that hard to do, all you need is Nero and the core DOS files.
What I would like is to buy a motherboard without the Floppy slot or PATA slots, devoting the entire board to SATA. You would be able to make the board a great deal smaller if you remove both the Floppy and PATA slots. You could probably do a micro ATA down to just a little bit larger than a Gamecube with the RAM slots, CPU and PCI-E slots taking up most of the space.
Total Serial ATA Speeds
SATA 1: 150 MB/s (Megabyte per second)
SATA 2: 300 MB/s
SATA 3: 600 MB/s
Total PCI Express Speeds
These speeds are bi-directional, meaning that are the same going both ways and not shared. However, for most applications, you will be sending more information to the card then it is going to send back to the CPU.
PCI-E x1: 250 MB/s
PCI-E x4: 1000 MB/s
PCI-E x8: 2 GB/s
PCI-E x16: 4 GB/s (Used for Graphic Layer also)
PCI-E x32: 8 GB/s
They are talking about in the future, changing the speeds from 2.5 Gb/s to 5 Gb/s and then to 10 Gb/s. A look at what that would be is totally crazy.
5 Gb/s
PCI-E x1: 500 MB/s
PCI-E x16: 8 GB/s
PCI-E x32: 16 GB/s
10 Gb/s
PCI-E x1: 1 GB/s
PCI-E x16: 16 GB/s
PCI-E x32: 32 GB/s
We are looking at 10+ years of time before PCI-E goes over to 10Gb/s in my opinion. It is crazy now to think that it is needed, except for gaming. Even gaming GPU doesn’t even use all of the available bandwidth on the current 4GB it has. It would be nice to have 8 GB, but that is actually like 16GB total going both ways. The Serial ATA and PCI-Express makes available far more speed than IDE and PCI, which would probably require 128 lanes making boards even larger and more complex.
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Nice article, however your math sucks, you’re removing the 2 of 10 bit overhead twice. Assuming that the numbers given by the SATA standard are using M and G in the Si usage (1000 not 1024, which will give us lower numbers anyway, 1.5Gb/s = 1500Mb/s) then your math should be:
1500Mb/s * 8_data_bits/10_actual_bits = 1200 data_bits/s
1200 data_bits/s / 8 b/B = 150B/s
You do “lose” speed due to the overhead, but that pulls the speed from the actual 188B/s to the effective 150B/s.
better late than never…
this looks to be an article written in 2006 ?
I’m replying mid 2008.
It’s interesting to see the focus of this write up about the
speed of a hdd actually focused on the speed of the "interface" that
connects the hdd to the motherboard.
The actual maths associated with the interface, lead you to believe the
interface actually determinds the speed difference of the hdd.
I’m sorry to say the interface whether it be ide, ata, sata, does not determine the internal capabilities of the actual hdd speed.
Recently in 2008 hdd speeds topped 100mb/s internal capabilities, so whether your using a ata 133, sata 150, 300 is irrelevant.
The speed at which data is moved thru this really big pipe (interface) is
not determinded by the connector or interface capability, it’s determinded by the internal capabilities of the hdd’s components.
The truth that the hdd advertised as ata 133 or sata 150 being "faster", is in fact incorrect and was when you wrote this article.
A hdd using a 133 or 150 interface would transfer data at exactly the same speed is true.
The truth of the matter is that hdd advertising has for a very long time been focused on the interface speed capabilities and not the speed at which a hdd factually transfers data.
It’s alittle unfortunate that this has occured as hdd speeds have increased very little in the past 5-10 years due to this.
In 2002 when i built my computer the speed of my hdd was approx 40mb/s.
I have installed 5 other hdd to my system over the last 6yrs, and the best speed one is running in the 60-70mb/s.
Maybe if the focus of hdd’s was restored to it’s actual capabilities of moving data instead of the interface max speed, then we might see some larger improvements in hdd.
@mac
I believe I understood at one point that there was a the internal speed differences and the interface speed. However, without the interface speed being able to push the bandwidth they there is no incentive for hard drive manufactures to increase the internal performance.