comparing: USB vs. IDE

dnewhous · Feb 5, 2004

I have been told that USB is "CPU intensive" but I don't have a low-level understanding of how it works. Is USB any worse at utilizing the CPU and motherboard than IDE?
I realize USB and IDE are used for different things but I think this comparison will enable me to learn the most.

don256us · Feb 6, 2004

The most simple way to understand this is:

USB does not have it's own controllers. That is to say, USB devices need the CPU to do number crunching.

IDE does have it's own controllers. Your HDD (for example) can process it's own data for use. Very little is required of the CPU.

Hope that helps some.

Como · Feb 6, 2004

yes, a usb device will use your cpu to do everything, while an ide device will just accept the data, usually directly from the ram ( i think ide uses DMA...or was that outdated? i hate having to study outdated technology)

usb is also a serial connecyion, rated for 12 MBPS, while IDE is paralell, rated for 33MBPS. EIDE is what most of us referr to as IDE, which goes as fast as 133 MBPS.

USB2 is rated for something like 400 MBPS, which is...fast...but every bit of data that goes to USB goes through the CPU via an IRQ, or interupt request.

whenever a usb device needs something, it interupts the cpu with its reques, then the cpu uses its power to give usb what it wants.

IDE on the other hand, each device has its own controller and can work almost independantly, where the CPU jsut sets up the connection between the ide device and the ram, and the motherboard takes care of it from there (i think...and if so that is DMA, i think....)

my understanding of all this is a little rusty/shakey, so correct me if need be

dnewhous · Feb 7, 2004

and now RS232

Switching gears a little here, how CPU intensive is RS232?

UPCguy21 · Feb 8, 2004

I forget exactly about rs232, but I think rs232 is more like for configuring telephone switches and routers, or for a CTI port, I'm thinking it's like a 300 baud connection, pretty slow. Someone correct me if I'm wrong...

dnewhous · Feb 8, 2004

You're wrong and I'm correcting you. The maximum baud rate of RS232 is 115200.

UPCguy21 · Feb 8, 2004

ok, I'm thinking I heard the 300 baud thing in my voice networking class, when we were talking about older equipment, like older telephone switches. Maybe that's where they started out at then. Thanks for the correction though.

tom10167 · Feb 8, 2004

"baud" holy crap there's a word I haven't heard in AGES.

mR. STuPiD · Feb 8, 2004

Como said:
yes, a usb device will use your cpu to do everything, while an ide device will just accept the data, usually directly from the ram ( i think ide uses DMA...or was that outdated? i hate having to study outdated technology)

usb is also a serial connecyion, rated for 12 MBPS, while IDE is paralell, rated for 33MBPS. EIDE is what most of us referr to as IDE, which goes as fast as 133 MBPS.

USB2 is rated for something like 400 MBPS, which is...fast...but every bit of data that goes to USB goes through the CPU via an IRQ, or interupt request.

whenever a usb device needs something, it interupts the cpu with its reques, then the cpu uses its power to give usb what it wants.

IDE on the other hand, each device has its own controller and can work almost independantly, where the CPU jsut sets up the connection between the ide device and the ram, and the motherboard takes care of it from there (i think...and if so that is DMA, i think....)

my understanding of all this is a little rusty/shakey, so correct me if need be

There's a bit more of a distinction here. USB 1.1 is 12 megaBITs per second, and 2.0 is 480(i think) megaBITs per second. IDE is 33-133megaBYTEs per second. A byte is 8 bits. Its a common mistake really. So USB is only 1.5 megaBYTES per second and usb 2.0 is only 60megaBYTEs per second, yet they never even reach those speeds. So there is a big difference between IDE and USB in speed. Also ussually usb is powered, meaning that the cable also carries a current. Thats why you can have little usb hard drives that don't need a power connection, but you don't have ide hard drives that run without being plugged into the power supply. Oh, and rs232 is a standard used by serial ports. dnewhous is correct on its speed. A baud may carry 1 to 16 bits depending on the encoding. I think for serial ports its just one, so in that case 115200baud is 115200bps.

MuEagle05 · Feb 8, 2004

yeah, that's right up there with 'parallel port' and '5.25inch floppy'

dnewhous · Feb 9, 2004

Parallel ports will do 3 to 5 Mbits per second.

I am asking about serial because I am comparing USB external analog modems to serial analog modems. I don't want to waste a PCI slot on a modem and I want to have one analog modem that sticks with me even when I change computers and even when the PCI bus shortly becomes obsolete (that's a prediction). I have DSL right now but I move every couple of years.

Another prediction: V.92 is the end of the road for analog modem technology - what is state of the art now will be state of the art for the next 20 years at least.

Cjwinnit · Feb 9, 2004

mR. STuPiD said:
Also ussually usb is powered, meaning that the cable also carries a current. Thats why you can have little usb hard drives that don't need a power connection, but you don't have ide hard drives that run without being plugged into the power supply.

True. Of the four wires in USB, there are two seperate circuits. One is for data (Data and ground) and one is a power circuit (+5 V and ground). I think you can run up to (maybe more) 600mA off a motherboard USB port, but it varies.

Como · Feb 9, 2004

"There's a bit more of a distinction here. USB 1.1 is 12 megaBITs per second, and 2.0 is 480(i think) megaBITs per second. IDE is 33-133megaBYTEs per second. A byte is 8 bits. Its a common mistake really. So USB is only 1.5 megaBYTES per second and usb 2.0 is only 60megaBYTEs per second, yet they never even reach those speeds."

well, i knew about the bits/bytes difference, but that sounds WAY off to me...
too bad i cant remember how many a mega is...someone wanna show the math to convert a megabit to a megabyte? my attempts are giving me way off conversions... and it doesnt help there are 3 girls in here talking about their computers crashing and how fast they burn cd's and one bragging about the mac she has and i just cant think cuz i'm trying not to scream...heh. (i'm at school)

JigPu · Feb 9, 2004

1 MB/sec = 8 Mb/sec
X MB/sec = 8*X Mb/sec

1 Mb/sec = 1/8 MB/sec
X Mb/sec = X/8 MB/sec

And.....
Kilo=Thousand, Mega=Million, Giga=Billion, Tera=Trillion
1024 KB/MB, 1024 Kb/Mb
1024 MB/GB, 1024 Mb/Gb
1024 GB/TB, 1024 Gb/Tb

So....
500Kb = 500/1024 Mb = (500/1024)/8 MB

JigPu

Steve978 · Feb 9, 2004

So whats the advantage of firewire because its transfer rate is less than usb 2.0 i think... does it have its own controllers?

Cjwinnit · Feb 9, 2004

Steve978 said:
So whats the advantage of firewire because its transfer rate is less than usb 2.0 i think... does it have its own controllers?

Firewire can transmit data in both directions at the same time (It's Full duplex) and is less CPU intensive.

moz_21 · Feb 9, 2004

Cjwinnit said:
True. Of the four wires in USB, there are two seperate circuits. One is for data (Data and ground) and one is a power circuit (+5 V and ground). I think you can run up to (maybe more) 600mA off a motherboard USB port, but it varies.

500mA per port MAX and I am quite sure it cannot vary.

Cjwinnit · Feb 9, 2004

moz_21 said:
500mA per port MAX and I am quite sure it cannot vary.

Well when I mean it varies I meant that not all USB ports will push that amount of current, although it's enough to run stuff like mice and keyboards

moz_21 · Feb 9, 2004

Sorry... what I meant was, Isn't that a requirement (of the USB spec)? I looked through the techdocs but I couldn't find the amperage, although I did see several references to 400mA. I dunno...

Mr.Radar · Feb 9, 2004

There is a new FireWire (IEEE1394) standard out there called IEEE1394b or FireWire800 that operates at 800Mbps [THAT'S BITS], but not too much supports it right now.

comparing: USB vs. IDE

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