Metric and Binary Quantities

Working with computers requires knowing some terminology referring to large quantities of data. You are probably familiar with metric prefixes such as "kilo-" and "mega-" in terms like kilogram and megawatt from science classes. However, computers use base 2, not base 10, so the metric prefixes don't quite fit when referring to common computer quantities.

Table 14.2, “Prefixes for larger quantities” shows a separate set of binary prefixes representing powers of 2 that are close to the powers of 10 used by the metric prefixes. They use the same first two letters as the metric prefix, followed by 'bi' (from binary).

Metric and binary prefixes are often confused and interchanged. This is not a problem where precision is not critical, such as in casual conversation, since they represent similar values. For example, it is often stated that a computer has 4 gigabytes (4 * 109 bytes) of RAM, when in fact it has 4 gibibytes (4 * 230 bytes).

In fact, using binary terms like gibibyte in casual conversation with non-technical people might make them think you've been drinking too much.

Table 14.2. Prefixes for larger quantities

Metric prefixAbbreviatedValueBinary prefixAbbreviatedValue
kilo-K-10^3kibi-Ki-2^10 (1,024)
mega-M-10^6mebi-Mi-2^20 (1,048,576)
giga-G-10^9gibi-Gi-2^30 (1,073,741,824)
tera-T-10^12tebi-Ti-2^40 (1,099,511,627,776)
peta-P-10^15pebi-Pi-2^50 (1.12589990684e+15)
exa-E-10^18exbi-Ei-2^60 (1.15292150461e+18)
zetta-Z-10^21zebi-Zi-2^70 (1.18059162072e+21)
yotta-Y-10^24yobi-Yi-2^80 (1.20892581961e+24)

The abbreviated forms of the binary prefixes are the same as the metric, but with an 'i' inserted. For example, 2 GB means 2 gigabytes, while 2 GiB means 2 gibibytes.



Be sure to thoroughly review the instructions in Section 2, “Practice Problem Instructions” before doing the practice problems below.
  1. You meet an attractive fashion designer at a party who seems impressed that you're a computer engineer, and proceeds to tell you that [s]he just bought a new laptop with "16 gigabytes" of memory. The correct response (assuming you want the conversation to continue) is:

    1. "Very cool. Does it help much with your design modeling?"
    2. "Since you're only a fashion designer, I'm not surprised that you would confuse gigabytes with gibibytes. RAM sizes are always a power of two, so you can never really have 16 gigabytes of RAM. Giga- is a metric unit. Don't feel bad, though, 'cuz smart people make the same mistake sometimes."
    3. "I personally would never buy a computer with less than 32. Modern operating systems and applications are memory pigs because the programmers are mostly idiots, but I don't have time to rewrite everything for them so I just fork over a few bucks for more hardware to work around their incompetence."
    4. Other (write your response here).