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Mixing Memory Unit Messages

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One of my pet hates is developers messing up units of memory.  In general, the difference doesn't matter much, or you can work out what they meant to say, but it does annoy me when developers who should know better appear to be confused about what they are trying to say.

From Wikipedia's Byte page, here is a cheat sheet of units

"b" means bits
"B" means bytes
"k" or kilo- is standard prefix meaning 1000
"K" or "Ki", sometimes called kibi- is 1024
"m" or mill-, means 1/1000th
"M" or mega-, means 1000^2
"Mi" or mebi-, means 1024^2 

 Unit     Meaning      In bytes
mb    
milli-bits1/8000th of a byte
mB    
milli-bytes1/1000th of a byte
kb    
kilo-bits
125 bytes
kB    
kilo-bytes
1000 bytes
Kb or Kib    
kibi-bits
128 bytes
KB or KiB    
kibi-bytes
1024 bytes
Mb    
mega-bits
125,000 bytes
MB    
mega-bytes
1,000,000 bytes
Mib    
mebi-bits
131,072 bytes
MiB    
mebi-bytes
1,048,576 bytes


What annoys me is when professionals confuse these terms. 

In UNIX:

In top on Unix it states

KiB Mem:  32893900


but when I do "head -1 /proc/meminfo" it states

MemTotal:       32893900 kB

this is 2.4% less. 

I suspect top is correct as it is closer the amount of memory installed and they used "KiB" which lends credibility, but I can't be sure.

In the JVM

The default translation for "KBYTES" is "kbytes" but in Japanese and Chinese it is "KB" which is 2.4% more.

While the JVM appears to be using KiB or kibibytes every where, it refers to "KiB" only three times, but uses "kB" in twice, "Kb" in seven places, "KB" in 127 places and "kilobytes" in three cases.

Similarly "MiB" appears 4 times, "MB" in 87 places, "Mb" three times and "mb" three times.

Puzzle

Question: A computer program writes to memory at 49 mb/s, to disk at 50 mb/s and to the network at 100 mb/s. Which is it writing data at a higher rate to; the memory, the disk or the network?
Answer: It is probably writing to memory most and the network least.  This is because it might be read as "... to memory at 49 MiB/s, to disk at 50 MB/s and to the network at 100 Mb/s. " and one MiB/s is almost 8.4 Mb/s

Conclusion

If you don't know what units you have in mind and which ones you don't, it shouldn't be surprising if someone reading your output is confused as well.

I encourage everyone to use standard units in their code so when you see units you know exactly what they mean.

The Performance Zone is brought to you in partnership with AppDynamics.  See Gartner’s latest research on the application performance monitoring landscape and how APM suites are becoming more and more critical to the business.

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Published at DZone with permission of Peter Lawrey, DZone MVB. See the original article here.

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