## Units

In computers, information is stored electronically as the binary digits 0 and 1, also referred to as 'off' and 'on' respectively.

• bit (1 b). One binary digit. The word "bit" is a contraction of 'binary' and 'digit'. The smallest unit of binary info.
• nibble (4 b = 0.5 B)
• byte (B = 2^3 b = 8 b). A byte is composed of 8 bits. A byte is equivalent to one ASCII character.
• word (16 b = 2 B). Size of a Unicode character in UTF-16.
• double word (32 b = 4 B). Size of Unicode character in UTF-32.
• quad word (64 b = 8 B).
• tenbyte (80 b = 10 B).
• paragraph (128 b = 16 B).
• page (32,768 b = 4,096 B). Assumes an ASCII text page at 8 b/character by 64 characters/line by 64 lines/page.

Beware that people get their bs and Bs mixed up! Except for shysters, most people should try to be consistent with using bits (b) when discussing rates and bytes (B) when discussing storage. Sometimes what is expressed in bits, actually refers to bpp (bits per pixel).

Since bits and bytes are binary, their multiples are also  expressed in binary powers: 2^10, 2^30, 2^40, 2^50, 2^60. While almost everyone is consistent about meaning binary powers for bits, there is a lot of inconsistency when it comes to bytes.

• The IEEE has suggested that small prefixes refer to decimal powers (EG: kb = 1000 b) and capital prefixes refer to binary powers (EG: Kb = 1024 b, while kb = 1000 b) but practically no one is consistent with this. EG: A "100 MB" disk by IEEE standards would be 100 MB = 100*2^20 B = 1.05E8 B = 1.05 mB, but the author of it may actually mean the smaller value of 100 mB = 100*10^6 B = 1.00E8 B = 95.4 MB. Also this sort of dilutes the purity of the SI prefixes.
• The IEC (International Electrotechnical Commission) with standard 60027 has suggested using binary power prefixes that are different from metric's decimal power prefixes. EG: A kilobinary has a prefix of "kibi", a symbol of "Ki", and means 2^10 or 1024. This is removes ambiguity for binary powers but when people use the metric prefixes we can't tell if they mean decimal or binary powers.

My solution would remove all ambiguity by using the IEC system but also add new prefixes for decimal powers. EG: "MiB" for binary and "MeB" for decimal! I think it's a brilliant idea that I came up with today [2004-07-31].

Multiple Prefix Metric Symbol GH Multiple Name Prefix Symbol 1e24 yotta Y Ye 280 ~ 1.21e24 yottabinary Yobi Yi 1e21 zetta Z Ze 270 ~ 1.18e21 zettabinary Zebi Zi 1e18 exa E Ee 260 ~ 1.15e18 exabinary exbi Ei 1e15 peta P Pe 250 ~ 1.13e15 petabinary pebi Pi 1e12 tera T Te 240 ~ 1.10e12 terabinary tebi Ti 1e09 giga G Ge 230 ~ 1.07e09 gigabinary gibi Gi 1e06 mega M Me 220 ~ 1.05e06 megabinary mebi Mi 1e03 kilo k --> K Ke 210 ~ 1.02e03 = 1024 kilobinary kibi Ki

Since this is my site, it shall be the law on this site henceforth. --> 2005-04-20: No way! My system was too annoying. Henceforth, my site will use SI prefixes (K, M, G, T, P, etc.) for binary units but the multiple will be binary powers instead of decimal. EG: When I say "4 MB", I mean "4 * 2^20 bytes" instead of "4e6 bytes".

For reference, here are common powers of 2:

Power Decimal Decimal
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
...
31
32
..
63
64
...
127
128
1.00e+0
2.00e+0
4.00e+0
8.00e+0
1.60e+1
3.20e+1
6.40e+1
1.28e+2
2.56e+2
5.12e+2
1.02e+3
2.04e+3
4.09e+3
8.19e+3
1.63e+4
3.27e+4
6.55e+4
1.31e+5
2.62e+5
5.24e+5
1.04e+6
...
2.14e+9
4.29e+9
...
9.22e+18
1.84e+19
...
1.70e+38
3.40e+38
1
2
4
8
16
32
64
128
256
512
1,024
2,048
4,096
8,192
16,384
32,768
65,536
131,072
262,144
524,288
1,048,576
...
2,147,483,648
4,294,967,296
...
9,223,372,036,854,775,808
18,446,744,073,709,551,616
...

## Common Sizes

• Data chunks and address size in DOS and Window 3.X (16 b)
• Data chunks and address size in Windows 95 and Windows NT (32 b)
• block in a sector in a track in a hard drive (512 KB)
• 3.5" HD (High Density) disk (1.44 MB)
• Iomega's Zip Drive 1 (100 MB)
• USB drives (aka USB sticks, key drives, pocket drives, memory sticks, etc.) (128 MB to 1 GB)
• Iomega's Zip Drive 2 (250 MB)
• MD (Mini Disk) (300 MB)
• CD, CD-R, CD-RW (650 MB)
• Iomega's Zip Drive 3 (750 MB)
• Hi-MD (1 GB)
• Iomega's Jaz Drive (1 or 2 GB)
• Castlewood's ORB Drive (2.2 GB)
• DVD-RAM (2.6-9.0 GB)
• DVD, DVD-R, DVD+R, DVD-RW, DVD+RW (4.7 GB)
• QIC Magnetic Tapes (40 MB to 10 GB)
• Iomega's Ditto Drive (2-10 GB)
• HD-DVD (15 GB or 30 GB if duql layer)
• Blu-ray DVD (25 GB or 50 GB if dual-layer)
• Iomega's REV Drive (35 GB or 90 GB compressed)
• DVD-R9, DVD+R9 (8.5 GB single side)
• HVDs (Holographic Versatile Disc) (1 TB)

## Common Rates

Rates are also commonly expressed in bits per second (bps or b/s), kbps (Kb/s), Mbps (Mb/s), and Gbps (Gb/s). Note that it is in BITS not BYTES.

• analog modem rates (1.2, 2.4 (1980s), 9.6 (early 1990s), 14.4, 28.8, 33.6, 56.6 Kb/s)
• POTS (Up to 56.6 Kb/s)
• frame relay (56 Kb/s to 45 Mb/s)
• DDS or DSO or ISDN (64 or 128 Kb/s)
• satellite modem (400 Kb/s)
• DSL (512 Kb/s to 8 Mb/s)
• Wi-Fi/802.11 (1-2 Mb/s at 2.4 GHz)
• DS1 or T1 (1.536 or 1.544 Mb/s)
• wireless microwave (1.544 Mb/s)
• 3G (384 Kb/s to 2 Mb/s)
• Bluetooth (1-2 Mb/s at 2.4 GHz)
• E-1, DS-1 Europe (2.048 Mb/s)
• ATA-1 = ATA = IDE (4 Mb/s)
• token ring networks (4-16 Mb/s)
• SCSI-1 (3.5-5 Mb/s)
• WiMax (3-6 Mb/s)
• DS2 or T2 (6.312 Mb/s)
• HSPA (1-7.2 Mb/s)
• E2 (8.448 Mb/s)
• Cat 3 (10 Mb/s)
• Ethernet networks (10 Mb/s)
• SCSI-2 = Fast SCSI = Fast Wide SCSI (10-20 Mb/s)
• Wi-Fi/802.11b (11 Mb/s at 2.4 GHz for 50 m)
• 4G (5-12 Mb/s)
• USB 1.1 (12 Mb/s)
• ATA-2 = EIDE = Fast ATA = Fast IDE/Ultra ATA (16.6 Mb/s)
• Cat 4 (20 Mb/s)
• SCSI-3 = Ultra SCSI = Ultra Wide SCSI (20-40 Mb/s)
• ATM (25-622 Mb/s)
• cable modem (512 Kb/s to 30 Mb/s; realistically download at 1.5 Mb/s and upload at 0.3 Mb/s or analog modem rates)
• ATA-4 = ATA/33 (33 Mb/s)
• E3 (34.368 Mb/s)
• Ultra2 SCSI = Ultra2 Wide SCSI (40-80 Mb/s)
• DS3 or T3 (44.736 Mb/s)
• OC-1/STS-1 (51.85 Mb/s)
• Wi-Fi/802.11a (25-54 Mb/s at 5 GHz for 30 m)
• Wi-Fi/802.11g (25-54 Mb/s at 2.4 GHz for 30m)
• ATA-5 = ATA/66 (66 Mb/s)
• WiMax/802.16 (70 Mb/s)
• FDDI (80 Mb/s)
• ATA-6 = ATA/100 (100 Mb/s)
• Cat 5 (100 Mb/s)
• CDDI (100 Mb/s)
• DQDB (100 Mb/s)
• FDDI (100 Mb/s)
• Fast Ethernet (100 Mb/s)
• ATA-7 = ATA/133 = PATA (133 Mb/s)
• OC-3/STS-3 (155.52 Mb/s)
• Ultra3 SCSI (160 Mb/s)
• Wi-Fi/802.11n (200-540 Mb/s at 2.5 or 5 GHz for 50 m)
• Ultra320 SCSI = Fast 320 (320 Mb/s)
• Firewire/Firewire 400/Apple IEEE 1394 (400 Mb/s)
• OC-9 (466.56 Mb/s)
• USB 2 (480 Mb/s)
• OC-12/STS-12 (622.08 Mb/s)
• Ultra640 SCSI
• Firewire 800/IEEE 1394b (800 Mb/s)
• OC-18 (933.12 Mb/s)
• 1 Gigabit Ethernet (1 Gb/s)
• OC-24 (1.244 Gb/s)
• SATA 1 = SATA/150 (1.5 Gb/s)
• OC-36 (1.866 Gb/s)
• SATA 3 = SATA/300 (3.0 Gb/s)
• OC-48/STS-48 (2.488 Gb/s)
• OC-96 (4.976 Gb/s)
• USB 3 (5 Gb/s)
• OC-192 (10 Gb/s)
• 10 Gigabit Ethernet (10 Gb/s)
• OC-255 (13.2 Gb/s)
• OC-256 (13.271 Gb/s)
• OC-768 (40 Gb/s)
• Thunderbolt (20-100 Gb/s for 3 m)

Page Modified: (Hand noted: 2007-10-24 04:49:49Z) (Auto noted: 2011-04-11 21:04:36Z)