# Dracula's Definitions of Computer Memory Sizes

=== by Bob Sutherland ===

## Modern Measuring Units for Computer Memory

Throughout my lifetime the field of Computer Science was very much in a state of flux as rapid advances were being made. As a result not everyone was going to be happy about using the traditional measuring units for computer memory size that I described on the previous page.

One group that would protest was the metric purists. They thought that it was pure blasphemy that we could take the prefixes of the International System of Units (SI) and apply them to powers of 2 and 1024 instead of using their sacred powers of 10 and 1000.

Another group that would protest was the inventors and manufacturers of computer memory storage devices such as CDs, DVDs, computer hard drives, computer memory sticks and flash drives. A CD has no wires so there is no logical reason to be using a system based on binary numbers when measuring a CD's memory capacity.

Finally there was the telecommunications industry who never accepted the byte as their main unit of computer memory size. They have always used bits as their main unit when measuring the speed of modems to transmit data over telephone lines, television cables and satellite signals.

The Joint Electron Device Engineering Council Solid State Technology Association (JEDEC), the International Electrotechnical Commission (IEC) and the International Organization for Standardization (ISO) are groups that have tried to create standard sets of computer memory unit names and letter symbols that they hoped everyone would adopt and follow. Unfortunately most people have probably never heard of these standardization committees and their decisions. As a result their suggested lists of computer memory unit names have just added confusion to the whole situation.

Here are the current lists of computer memory sizes. You will probably find that many large companies in the computer and telecommunications industries are using one of these lists. The problem then becomes trying to figure out which list they are using. Are the advertising and engineering departments within a company using the same list?

Metric version based on byte units
Unit NameSymbol
Bit is the smallest unit of computer memory size.
Byte = 8 bits
KilobytekB103 bytes10001 bytes= 1000 bytes
MegabyteMB106 bytes10002 bytes= 1000 kilobytes
GigabyteGB109 bytes10003 bytes= 1000 megabtyes
TerabyteTB1012 bytes10004 bytes= 1000 gigabytes
PetabytePB1015 bytes10005 bytes= 1000 terabytes
ExabyteEB1018 bytes10006 bytes= 1000 petabytes
ZettabyteZB1021 bytes10007 bytes= 1000 exabytes
YottabyteYB1024 bytes10008 bytes= 1000 zettabytes
Binary IEC version based on byte units
Unit NameSymbol
Bit is the smallest unit of computer memory size.
Byte = 8 bits
kibibyteKiB210 bytes10241 bytes= 1024 bytes
mebibyteMiB220 bytes10242 bytes= 1024 kibibytes
gibibyteGiB230 bytes10243 bytes= 1024 mebibytes
tebibyteTiB240 bytes10244 bytes= 1024 gibibytes
pebibytePiB250 bytes10245 bytes= 1024 tebibytes
exbibyteEiB260 bytes10246 bytes= 1024 pebibytes
zebibyteZiB270 bytes10247 bytes= 1024 exbibytes
yobibyteYiB280 bytes10248 bytes= 1024 zebibytes
Binary IEC version based on bit units
Unit NameSymbol
Bit is the smallest unit of computer memory size.
KibibitKibit210 bits10241 bits= 1024 bits
MebibitMibit220 bits10242 bits= 1024 kibibits
GibibitGibit230 bits10243 bits= 1024 mebibits
TebibitTibit240 bits10244 bits= 1024 gibibits
PebibitPibit250 bits10245 bits= 1024 tebibits
ExbibitEibit260 bits10246 bits= 1024 pebibits
ZebibitZibit270 bits10247 bits= 1024 exbibits
YobibitYibit280 bits10248 bits= 1024 zebibits
Metric version based on bit units
Unit NameSymbol
Bit is the smallest unit of computer memory size.
Kilobitkbit103 bits10001 bits= 1000 bits
MegabitMbit106 bits10002 bits= 1000 kilobits
GigabitGbit109 bits10003 bits= 1000 megabits
TerabitTbit1012 bits10004 bits= 1000 gigabits
PetabitPbit1015 bits10005 bits= 1000 terabits
ExabitEbit1018 bits10006 bits= 1000 petabits
ZettabitZbit1021 bits10007 bits= 1000 exabits
YottabitYbit1024 bits10008 bits= 1000 zettabits

## Exponent Charts

The Binary charts are based on wires and powers of two. They can also be expressed as powers of 1024.

The Metric charts use powers of 1000 rather than powers of 1024 to create alternative sets of computer memory size units.

Here are some exponent charts that will allow you to compare the difference in using powers of 1024 or powers of 1000.

Powers of 2 and 1024
2n1024mvalue
21010241= 1,024
22010242= 1,048,578
23010243= 1,073,741,824
24010244= 1,099,511,627,776
25010245= 1,125,899,906,842,624
26010246= 1,152,921,504,606,846,976
27010247= 1,180,591,620,717,411,303,424
28010248= 1,208,925,819,614,629,174,706,176
Powers of 10 and 1000
10n1000mnamevalue
10310001thousand= 1000
10610002million= 1,000,000
10910003billion= 1,000,000,000
101210004trillion= 1,000,000,000,000