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March 18, 2008 4:25 PM Subscribe
What is my baud rate?
I connect using Comcast (bad company! No!). When I am downloading a large file my d/l rate is usually around 650-700 Mbits/sec. What would that convert to if this was 1985 and I was using a hypothetical super-modem on my old Commodore 64?
I connect using Comcast (bad company! No!). When I am downloading a large file my d/l rate is usually around 650-700 Mbits/sec. What would that convert to if this was 1985 and I was using a hypothetical super-modem on my old Commodore 64?
Are you certain your download rate is 650-700 Mbits/sec? If I did my math correctly, that's around 80 megabytes/second, or roughly the rate you would get from something like an OC12, and I'm pretty sure you'd know it if you had one of those :) Let's assume you meant 650/700 kilobits/sec.
You might find a bandwidth calculator helpful for this kind of problem.
First of all, old modems used to specify speed as the baud rate instead of kilobits/sec (kbps), since they were generally equal. Faster modems did away with this, as the baud rate no longer equaled the data transfer rate. Since the baud rate isn't a particularly useful number, lets also assume you want to know the actual transfer speed. This is simply 650-700 kilobits/sec, or 650,000-700,000 bits/second.
Wikipedia tells us that a top of the line Commodore 64 modem could run at 1200 baud (1200 bits/second). In other words, your connection is about 540 times faster than your old modem.
I've doubtless fouled up some of the math. Please critique.
posted by zachlipton at 4:38 PM on March 18, 2008
You might find a bandwidth calculator helpful for this kind of problem.
First of all, old modems used to specify speed as the baud rate instead of kilobits/sec (kbps), since they were generally equal. Faster modems did away with this, as the baud rate no longer equaled the data transfer rate. Since the baud rate isn't a particularly useful number, lets also assume you want to know the actual transfer speed. This is simply 650-700 kilobits/sec, or 650,000-700,000 bits/second.
Wikipedia tells us that a top of the line Commodore 64 modem could run at 1200 baud (1200 bits/second). In other words, your connection is about 540 times faster than your old modem.
I've doubtless fouled up some of the math. Please critique.
posted by zachlipton at 4:38 PM on March 18, 2008
You can have multiple bits per baud. Checking around a bit: the C64 at some point got to use 56K modems, which transferred 56kbits at 8k baud, so 7 bits per baud. So, at that conversion rate: 700Mbits / 7 bits/baud = 100 million baud.
If you consider one bit to be one baud, which is imprecise but common, zixyer has it.
On preview, yeah, that's probably in kilobytes/sec. 700 kilobytes/sec -> 100 kilobaud.
posted by Pronoiac at 4:38 PM on March 18, 2008
If you consider one bit to be one baud, which is imprecise but common, zixyer has it.
On preview, yeah, that's probably in kilobytes/sec. 700 kilobytes/sec -> 100 kilobaud.
posted by Pronoiac at 4:38 PM on March 18, 2008
Damn you zachlipton!
Actually, look further down that C64 Wikipedia page for the 56k note. And my other link for, um, 1200 or 2400 bits/sec -> 600 baud.
posted by Pronoiac at 4:42 PM on March 18, 2008
Actually, look further down that C64 Wikipedia page for the 56k note. And my other link for, um, 1200 or 2400 bits/sec -> 600 baud.
posted by Pronoiac at 4:42 PM on March 18, 2008
Yeah my bad for missing the 56k modems. I remember 56k (and far slower) modems, but I'm too young to have gotten into the C64 craze, and apparently also too young to read to the bottom of the Wikipedia section.
posted by zachlipton at 4:47 PM on March 18, 2008
posted by zachlipton at 4:47 PM on March 18, 2008
Yeah, what you're getting is 650-700Kbits, which is...eh, 6-ish megabits. That's Mb. Divide that by 8 and that's how many megaBYTES per second.
It gets a little confusing with Kb, KB, Mb, and MB. (bits get a small b. bytes get a big B, and a byte is 8 bits.)
posted by TomMelee at 5:33 PM on March 18, 2008
It gets a little confusing with Kb, KB, Mb, and MB. (bits get a small b. bytes get a big B, and a byte is 8 bits.)
posted by TomMelee at 5:33 PM on March 18, 2008
Remember that most modems transmit multiple bits per baud. For example, a 2400 bps modem runs at 600 baud and transmits 4 bits per baud. Your 9660 bps modems were 2400 baud and 4 bits per baud.
posted by kindall at 5:57 PM on March 18, 2008
posted by kindall at 5:57 PM on March 18, 2008
There are two separate issues here: The question of baud vs. bits per second, and the question of "how many bits per second am I getting when I use my Internet connection to download a large file?"
It turns out that when people said things like "I have a 2400 baud modem," or "I have a 9600 baud modem," they were technically incorrect. What they really meant was that their modems transferred 2400 or 9600 bits per second.
The "baud rate" of a modem actually means the number of symbols that are sent over the phone line each second. A so-called "300 baud modem" using the Bell 103 or V.21 protocol, transmitted 300 symbols per second, and so was a true 300 baud modem. Each symbol represented one bit: a 0 or a 1; hence, the modems transmitted 1 bit per baud, resulting in a total of 300 bits per second.
The so-called "1200 baud modem" (using the Bell 212A or V.22 protocol) was actually a 600 baud modem that transmitted 2 bits per baud, hence transferring 1200 bits per second. Each symbol transmitted by such a modem down the phone line represented two bits (using 4 possible tones transmitted over the phone line). One tone represented the bits '00', another represented '01', yet another represented '10', and the final tone represented '11'. By sending 600 of these symbols each second, the modem could transfer a total of 1200 bits per second.
A "2400 baud" modem actually transmitted 2 bits per symbol at 1200 baud,
A "9600 baud" modem transmitted 4 bits per symbol at 2400 baud,
A "14400 baud" modem transmitted 6 bits per symbol at 2400 baud,
A "28000 baud" modem transmitted 9 bits per symbol at 3600 baud,
And so on...
So, what was really being advertised on the front of the modem's packaging was the data throughput speed of the modem, as measured in bits per second.
As for the actual speed of your Internet connection: I think this has mostly been answered. If you are seeing values of 650-700 in a web browser, the web browser probably means 650-750 kilobytes per second (KB/s). This comes to 5,200,000 through 5,600,000 bits per second, or "baud," as a modem user might incorrectly have called it. This is equivalent to 5200-5600 kbps (kilobits per second), or 5.2 through 5.6 megabits per second.
5.6 mbit/sec is (5,600,000 / 2,400 = ) approximately 2,333 times faster than the transfer rate of a so-called "2,400 baud" (2,400 bits-per-second) modem.
posted by Juffo-Wup at 6:13 PM on March 18, 2008 [1 favorite]
It turns out that when people said things like "I have a 2400 baud modem," or "I have a 9600 baud modem," they were technically incorrect. What they really meant was that their modems transferred 2400 or 9600 bits per second.
The "baud rate" of a modem actually means the number of symbols that are sent over the phone line each second. A so-called "300 baud modem" using the Bell 103 or V.21 protocol, transmitted 300 symbols per second, and so was a true 300 baud modem. Each symbol represented one bit: a 0 or a 1; hence, the modems transmitted 1 bit per baud, resulting in a total of 300 bits per second.
The so-called "1200 baud modem" (using the Bell 212A or V.22 protocol) was actually a 600 baud modem that transmitted 2 bits per baud, hence transferring 1200 bits per second. Each symbol transmitted by such a modem down the phone line represented two bits (using 4 possible tones transmitted over the phone line). One tone represented the bits '00', another represented '01', yet another represented '10', and the final tone represented '11'. By sending 600 of these symbols each second, the modem could transfer a total of 1200 bits per second.
A "2400 baud" modem actually transmitted 2 bits per symbol at 1200 baud,
A "9600 baud" modem transmitted 4 bits per symbol at 2400 baud,
A "14400 baud" modem transmitted 6 bits per symbol at 2400 baud,
A "28000 baud" modem transmitted 9 bits per symbol at 3600 baud,
And so on...
So, what was really being advertised on the front of the modem's packaging was the data throughput speed of the modem, as measured in bits per second.
As for the actual speed of your Internet connection: I think this has mostly been answered. If you are seeing values of 650-700 in a web browser, the web browser probably means 650-750 kilobytes per second (KB/s). This comes to 5,200,000 through 5,600,000 bits per second, or "baud," as a modem user might incorrectly have called it. This is equivalent to 5200-5600 kbps (kilobits per second), or 5.2 through 5.6 megabits per second.
5.6 mbit/sec is (5,600,000 / 2,400 = ) approximately 2,333 times faster than the transfer rate of a so-called "2,400 baud" (2,400 bits-per-second) modem.
posted by Juffo-Wup at 6:13 PM on March 18, 2008 [1 favorite]
Back in the C-64 days, the words "baud" and "bits per second" were virtually interchangeable, at least on a practical level (and in typical usage). The Commodore 1670 was sold as a "1200 baud" modem, and it was 1200 bps -- that was the fastest one built specifically for the C-64 (and introduced in late 1985, so it would be the supermodem of which you speak). There were adapters and other hacks that would allow a 64 to use a (faster) third-party external modem, but outside of certain circles, or into the 90's when 2400 baud modems got cheaper, you didn't see them.
The number that Firefox is giving you when you download a large file is in Kilobytes per second (KB/sec). 600-700 KB/sec is typical for a fast DSL line or cable modem (it's 4.8-5.6 Megabits per second (Mb/sec), and is usually advertised as "up to 6Mbps")
OK. Let's put that into perspective. For sake of argument, assume your DSL line speed is 5 megabits/sec. That is 5,000 kilobits/sec, or 5,000,000 bits/sec. In the parlance of a C-64 user of 1985, you are using a Five Million baud modem.
A single-sided Commodore 1541 disk drive held 170 Kilobytes on a 5 1/4 disk. At 1200 bps, a full C-64 disk takes 19 minutes to download (in practice, with error correction and protocol overhead, and your sister picking up the phone, it's usually more, but I'm going by the numbers). At 5Mbps, it'll take you a little more than a quarter of a second.
If you were to hook a "1200 baud" modem from 1985 to your PC and download a large file, instead of seeing 600-700KB on the meter, you'd see 0.15 KB/sec (or more likely, "150 bytes/sec")
posted by toxic at 6:13 PM on March 18, 2008 [1 favorite]
The number that Firefox is giving you when you download a large file is in Kilobytes per second (KB/sec). 600-700 KB/sec is typical for a fast DSL line or cable modem (it's 4.8-5.6 Megabits per second (Mb/sec), and is usually advertised as "up to 6Mbps")
OK. Let's put that into perspective. For sake of argument, assume your DSL line speed is 5 megabits/sec. That is 5,000 kilobits/sec, or 5,000,000 bits/sec. In the parlance of a C-64 user of 1985, you are using a Five Million baud modem.
A single-sided Commodore 1541 disk drive held 170 Kilobytes on a 5 1/4 disk. At 1200 bps, a full C-64 disk takes 19 minutes to download (in practice, with error correction and protocol overhead, and your sister picking up the phone, it's usually more, but I'm going by the numbers). At 5Mbps, it'll take you a little more than a quarter of a second.
If you were to hook a "1200 baud" modem from 1985 to your PC and download a large file, instead of seeing 600-700KB on the meter, you'd see 0.15 KB/sec (or more likely, "150 bytes/sec")
posted by toxic at 6:13 PM on March 18, 2008 [1 favorite]
Also, in early days, the serial line between your computer and your modem had to run at the same bit rate as the 'phone connection. This was true for a while even after modem technology started transmitting multiple bits per symbol (with the 1200bps/600baud Bell 212A modems). RS232 doesn't use any fancy coding, so the serial line was still literally at 1200baud. Eventually, modems started doing a lot of buffering, error-correcting, and packetization themselves, so you'd run the serial line at an arbitrarily high speed (115200baud, often) and rely on flow control to make everything work out.
posted by hattifattener at 8:38 PM on March 18, 2008
posted by hattifattener at 8:38 PM on March 18, 2008
To get really technical - on the baud rate discussions - it wasn't totally incorrect to say "9600 baud" either... on the modulated side, indeed, 9600 bps modems were 2400 baud. On the serial cable though, the symbol rate matches the signaling rate - so 9600 bps is 9600 baud.
The original question, though, as to what people would have called it back then -
We probably would have called 700mbps "seven hundred megabaud" or something clever like that, and then opened another beer, and continued to daydream about flying cars.
posted by TravellingDen at 8:40 PM on March 18, 2008
The original question, though, as to what people would have called it back then -
We probably would have called 700mbps "seven hundred megabaud" or something clever like that, and then opened another beer, and continued to daydream about flying cars.
posted by TravellingDen at 8:40 PM on March 18, 2008
On the serial cable though, the symbol rate matches the signaling rate - so 9600 bps is 9600 baud.
I think that might not be technically true, because (according to Wikipedia anyway) baud is used for modulated signals. I guess it could be applied to straight digital signals like RS-232 serial, but I think that would be a pretty unusual usage.
posted by kindall at 9:06 PM on March 18, 2008
I think that might not be technically true, because (according to Wikipedia anyway) baud is used for modulated signals. I guess it could be applied to straight digital signals like RS-232 serial, but I think that would be a pretty unusual usage.
posted by kindall at 9:06 PM on March 18, 2008
This thread is closed to new comments.
posted by zixyer at 4:29 PM on March 18, 2008