![]() ![]() I sometimes hear that HDMI 1.0 is 4.5 Gb/s, when it is really 3.6 Gb/s (TMDS encodes 8 bits for every 10 symbols as well). This sort of exaggeration seems to be becoming more common. (4 us symbol time, 288 coded bits per symbol, 216 data bits per symbol.) The 54 Mb/s data rate uses a 3/4 coding, i.e., for every 3 bits input, you get 4 coded bits on the air. If you rated 802.11a/g the same way it would be 72 Mb/s. The PHY has 200 ns symbol time (5 Gsymbols/s) but encodes the data with 8b/10b, i.e., every 10 symbols on the wire corresponds to 8 bits of information. ![]() The 5 Gb/s is marketing speak, the real, raw data rate is 4 Gb/s. Try to get more real-world than that, and you have to get specific about which real world you mean. The only unambiguous measure you can give is the raw bit signalling rate. Most people would say it's fraudulent to say 5E9/8 bytes travel down this line every second, since less than 80% of that number end up as actual bytes in computer memory. It complicates the picture a bit, but there are plenty of complications.Ĭo-opting the word "byte" as a unit of measure does complicate the picture, and it doesn't make anything less confusing, because there are so many levels on which to count the bits. You could point to a keg of beer and say it contains 6.9 cases of beer, but in fact there are no cases of beer in it.Ĭomputer memory and disk sectors, on the other hand actually have bytes in them. They're units of data.Ĩ bits don't make a byte like 12 inches make a foot. That wouldn't stop us from quoting in bytes.īut bytes aren't a unit of measure to be quoted. Posted 20:33 UTC (Sat) by giraffedata (guest, #1954) So what's with the 10:1 ratio between wire speed and real world speed for USB 3.0? And I could have sworn my current USB 2.0 drives have managed better than 4.5MB/s.Īnd why are we still quoting speeds in terms of bits per second in the year 2009? I thought we agreed upon a standard size for a byte a while back, and the proponents of '7' lost? It's said real-world transfer rates for USB 3.0 may be as much as 62.5MB per second, compared to 3MBps to 4.5MBps, offering the potential for 20x faster speeds. By comparison, Firewire (IEEE 1394) currently tops out at 400MBps. The spec is said to offer physical-layer throughput speeds of up to 625MBps compared to USB 2.0's 60MBps. Translating all of this to MBps (megabytes per second), for easier understanding. It's said real-world transfer rates for USB 3.0 may be as much as 500Mbps, compared to 25Mbps to 35Mbps for typical USB 2.0 mass storage drivers, offering the potential for 20x faster speeds. By comparison, Firewire (IEEE 1394) currently tops out at 3.2Gbps. The spec is said to offer physical-layer throughput speeds of up to 5Gbps (gigabits per second), compared to USB 2.0's 480Mbps (megabits per second). ![]()
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