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| Thread ID: 116630 | 2011-03-13 04:02:00 | bit and Bytes 101 | lostsoul62 (16011) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 1185718 | 2011-03-13 18:46:00 | On a hard drive you have to have a bit between every Byte Really? Hard disk drives are sealed system containing one or more magnetic discs inside. Each side is simply called side or head, because for each side there is a magnetic head available for reading and writing data. Each side of a magnetic disc is divided into several concentric tracks or cylinders. Then each track is divided into sectors. Each sector holds 512 bytes of information. The minimum unit the hard disk drive controller can access is the sector, meaning that if it has to read just one byte from a given sector, it must read the entire sector. The number of bytes inside a sector is fixed, it is always 512 bytes. But the number of tracks, sectors per track and sides (i.e., heads) a hard drive has will depend on the model. The number of heads, tracks and sectors per track a hard disk drive has is called geometry. If you multiply the number of heads by the number of tracks and then by the number of sectors per track you will find how many sectors a given hard disk drive has (for newer hard disk drives the manufacturer announces the number of sectors the drive has, instead of its geometry). Multiplying this number by 512 will give you the total capacity of a hard disk drive in bytes. |
pctek (84) | ||
| 1185719 | 2011-03-13 19:25:00 | I think what lostsoul was referring to was the physical bit layout on the disc surface. On the ground, so to speak, there are sector markers, ECC bits, etc. Plus the whole disc will be laid out with some sort of RLL encoding, as there has to be a polarity change in the signal read by the heads every so often. The end result would probably be more than even 9 or 10 bits per byte. So basically whenever you have to encode a sequence of (always 8-bit) bytes onto some sort of physical medium, you're going to have encoding overhead - often mitigated by some compression scheme running in parallel. |
MushHead (10626) | ||
| 1185720 | 2011-03-13 20:27:00 | The number of bytes inside a sector is fixed, it is always 512 bytes......unless you're talking about one of the newer drives which use a 4KB sector size. This also doesn't take into account operational overhead (error-correction etc) as MushHead has mentioned. | Erayd (23) | ||
| 1185721 | 2011-03-14 01:31:00 | really not sure what you are asking, perhaps you could make it clearer. yes 8 bits = 1 byte, and if you send any extra data such as crc etc it would either be contained within that 8 bits or more likely sent as part of the overhead as specified by whatever standard used. There would not be any random bits floating around, they would be formated into bytes themselves. The kilobyte thing is much less clear, it has part of it's roots in the fact that kilo, mega, tera etc are Decimal terms that were "borrowed" for use in the computer world. As such a kilobyte CAN be defined as either 1024 (the proper binary number) or 1000 bits (the literal translation of the word). Marketing people obviously chosse the one that sounds bigger. The move to use such terms as KiB etc to differentiate is a relatively new thing that hasn't been universally adopted. The old floppy is the worst of it as it uses a combination of the two. I forget the exact details but it's something like 1400 kb - ie' decimal amount of binary Kb |
dugimodo (138) | ||
| 1185722 | 2011-03-14 02:51:00 | Way back when I was a technician for Telecom data was sent using the ISO 7 layer model... (probably still is). The model is... (from layer 1 to 7 as below) Physical Link Network Transport Session Presentation Application Depending on which type of encoding was used there were varying 'packet' lengths. Packets included such information as addressing, error correction (CRC), and of course the data. Then there was the interleaving of packets, rerouting to avoid losses.... redundant paths, etc - quite complicated (and this was 20 odd years ago!) I used to be able to decipher packet streams on the fly when monitoring a connection !!! - no way now (LOL). So I agree - usually 9+ bits per packet (min)... Unless we are talking telex (whats that you ask? - Google it) where they used 6bits + 1 start & 1.5 stop bits......... and +/- 80 volt signals! - would give you a decent thump if you weren't careful.... Memories............... |
ManUFan (7602) | ||
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