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Definition: space/time


The following units of measure are used to define digital capacities and speeds. For measurements of a meter, see metric system. See binary values, NIST binary and long scale.

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                       10 to the
 Bits or Bytes         Power of:

 Kilo  (K)  Thousand       3
 Mega  (M)  Million        6
 Giga  (G)  Billion        9
 Tera  (T)  Trillion      12

 Bytes

 Peta  (P)  Quadrillion   15
 Exa   (E)  Quintillion   18
 Zetta (Z)  Sextillion    21
 Yotta (Y)  Septillion    24
 Bronto     Octillion     27
 Geop       Nonillion     30

 Storage Capacity Measured in:

 CPU word size        bits

 Disk/SSD/USB drive   bytes
 Memory (RAM)         bytes


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 Fractions of a second    10 to the
  Second                  Power of:

 Millisecond (ms) Thousandth     -3
 Microsecond (µs) Millionth      -6
 Nanosecond  (ns) Billionth      -9
 Picosecond  (ps) Trillionth    -12
 Femtosecond (fs) Quadrillionth -15
 Attosecond  (as) Quintillionth -18
 Zeptosecond (zs) Sextillionth  -21
 Yoctosecond (ys) Septillionth  -24


 Transmit/Transfer Measured in:

 Parallel bus/channel      bytes/sec
 Parallel disk drive       bytes/sec
 Memory (RAM)              bytes/sec

 Cellular data plan        bytes

 Serial bus/channel        bits/sec
 Serial disk drive         bits/sec
 Network & communications  bits/sec

 Disk access time          ms
 RAM access time           ns
 Machine cycle             µs, ns
 Instruction execution     µs, ns
 Transistor switching      ns, ps, fs


 CPU Speed - Clock Cycles Per Second
 See Hertz.

 kilohertz (kHz) thousand
 megahertz (MHz) million
 gigahertz (GHz) billion
 terahertz (THz) trillion