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Kilo, Mega, Giga: What Are These Computer Terms?

Updated on May 06, 2016

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What are all these terms?

It recently occurred to me that there are a literal ton of terms used in selling and marketing computers. These terms may not mean much to the vast majority of computer purchasers, but they are important.

So I thought I'd address these computer and Internet terms.They are terms that can actually be applied to many technical sciences, not just computing.

Why is Watt or Hertz capitalized in abbreviations and why are other terms not capitalized? What is a Watt? What is a Hertz? Check the end of this article for an answer. Maybe you too could become part of the library of terminology.

And why should you care if a drive is SSD or not; that a disc drive is SATA or PATA. I hope to answer these questions and more.

Kilo Mega Giga. What are these?

Some of the following terms are capitalized because the same letters are used for both directions of the scale. For example a lowercase "m" is used for micro because it's a fractional unit. Uppercase "M" is used if it's a multiplier.

These terms have their roots in a language rather than in the name of a specific person. They are Greek (literally) for units of measure. The units are very generic and can be applied to a number of other terms for a combined term.

Here are the "order of magnitude" terms and what they mean. Some are no longer in common use;

  • deca to the power of ten (101)
  • hecto to the power of one hundred (102)
  • Kilo to the power of one thousand (103)
  • Mega to the power of one million (106)
  • Giga to the power of one billion (109)
  • Tera to the power of one trillion (1012)
  • Peta to the power of one quadrillion (1015)
  • Exa to the power of one quintillion (1018)
  • Zetta to the power of one sextillion (1021)
  • Yotta to the power of one septillion (1024)

Rules are that orders of magnitude are capitalized above hecto.

By combining these terms with other units of measure you end up with a very handy multiplier in word form.

So for example if we wanted to know how fast a computer ran (it's clock speed) we might say that it runs at 2 GigaHertz or 2GHz. Or if we wanted to know how much power the computer consumed we might say it ran on 100 milli-watts or 100mW*.

So to put this into perspective a really fast computer would have the following parameters. It would have a Core 2 Duo processor (Core Duo was the processor prior to the Core 2 Duo). It would operate at or above 2.0GHz. That's GigaHertz. It would have a hard disc at or above 80GB. That's GigaBytes and have at least 2GB of memory operating at or above 667MHz, that's MegaHertz.

It will be a while before Tera starts being used, but likely sooner than any of us expect...including myself. Of course when this happens we'll be seeing numbers like 1TB, for TeraByte.

Microsoft recently upgraded the accessible performance of flash drives or solid state device(s) (SSD) by allowing a file size upper limit in the ExaByte (EB) range. This upgrade in file size upper limit is implemented in the Windows Vista Service Pack 1 released on February 4, 2008.

It will likely be decades (if ever) before we see Peta used with clock speed, but if we do it will be recorded as PHz or PetaHertz. I say "if ever" because quite frankly a processor that gets into these speed ranges will likely be nothing like the processors we see today which are based on semiconductor technology. A processor this fast would have to be based on an entirely different type of technology.

I would hazard to guess that a PetaHertz computer would operate on an atomic or sub-atomic level.

Going in the opposite direction you end up with terms that represent fractional units rather than multipliers. These units are represented by lower case letters. So, for example, "M" would be Mega, but "m" would be milli.

Here are the fractional units from largest to smallest.

  • deci one tenth (0.1)
  • centi one hundredth (0.01)
  • milli one thousandth (0.001)
  • micro one millionth (0.000001)
  • nano one billionth (0.000000001)
  • pico one trillionth (0.000000000001)
  • femto one quadrillionth (0.00000000000001)
  • atto one quintillionth (0.00000000000000001)
  • zepto one sextillionth (0.00000000000000000001)
  • yocto one septillionth (0.0000000000000000000001)

*milli is going in the opposite direction. Milli is one thousandth.

High numbers are good except when...

Generally speaking when talking about computer performance statistics, high numbers are better.

A computer with a 2.0GHz processor is faster than a computer with a 1.8GHz processor. Memory that operates at 667MHz is better than memory that operates at 500MHz. A computer with a 10 base T 1000 network connection is faster than a computer with a 10 base T 100 network connection. I think you get the general idea.

The exception to this rule is disc or memory access speed. In this area lower numbers are better as the less time to write or access a file or folder the faster the better. Interestingly manufacturers do not publish access speed figures very often.

So, using the scale for fractional units (above) a disc drive that can access data in the micro-seconds is going to be faster than one that can access data in the milli-seconds.


PATA & SATA are abbreviations for describing how information storage devices are connected to a computer system. In no way to these two terms define how fast a disc drive works or how much information one can contain. Rather these terms define how data is moved from a drive to (say) memory.

The "P" in PATA stands for parallel; the "S" in SATA for serial. The ATA in both cases is an abbreviation for the same thing.

ATA stands for Advanced Technology Attachment. Since the disc drive is "attached" to the computer via "advanced technology." Because there was only one original ATA interface (being was parallel) PATA and SATA did not come into common usage (as terms) until 2003 when a serial interface version was developed.

Parallel interfaces have a distance limit. This is due to the fact that so many data lines (sixteen and up) are required send and receive data simultaneously. In early versions there were sixteen and then up to twenty-eight data lines that could communicate to and from the drive simultaneously. The problem with so many independent wires being used is that they tend to become radio-antenna with length. They will quite literally pick up signals from outside (radio, TV, cell phone) and this in turn can corrupt signals meant to be confined to the cabling and in turn stored on the disc drive. I don't know about you, but I don't want someone's cell phone conversation mixed up with a letter I'm writing or a video I'm storing.

This is why there is a distance limit. This limit is anywhere from eighteen to thirty-six inches (three feet max) depending on the application. Clearly if the cabling is used in an enclosed metal cabinet greater lengths are unimportant and really unnecessary, but if the cabling must extend between one device and another, with an external drive for example, then length and potential corruption becomes an important consideration.

An attempt was made to extend this distance by providing a ground wire for every signal wire (which helps dampen signal problems), but this doubled the number of wires that had to be accounted for at both the cable ends. This is why ribbon cable looks like ribbon rather than wire.

Serial ATA does away with this problem and lengthens the distance signals can be sent over the wire. This was only possible with faster disc controller devices since the number of signal lines was reduced from sixteen (or more) to four (with seven wires total).

Advantages of SATA are;

  • Longer cable lengths permitted.
  • Higher data transfer rates than PATA
  • More efficient cooling inside the computer enclosure due to thinner cabling. Thin cables block less airflow than ribbon cabling.
  • The ability to queue data streams and write to disc when ready.

The first generation SATA interfaces were no faster than the PATA standard they replaced, but the current generation SATA interface doubled that speed. There is now a SATA standard in the works that will once again double the last speed increase. This next generation of SATA may not be that noticeable until it is joined with faster disc controllers, processors, and memory. Three other technologies that continue to evolve.

I won't go into the PATA pin specifications here; there are just too many, but the SATA pin-out (what each pin does) is;

  • Pins 1 through 3 data
  • Pins 4 through 6 ground for data

  • Pins 7 through 9 five (5) volts (power).
  • Pin 10 ground

  • Pin 11 spin-up signal (tells the processor when the disc are rotating at operational speed.
  • Pin 12 ground
  • Pins 13 through 15 twelve (12) volts (power).

A side note on Parallel vs Serial

The parallel vs serial path of progress has already played out in another area of the computer world; your printer.

Two decades ago there were two ways to connect a printer to your computer. Via a parallel cable or a serial cable. Then as now, or rather recently, parallel was the preferred method of connecting a printer because the signal processing was fast and with a fast enough printer you could get reams of printouts quickly. The drawback, of course, was your printer had to be very close to the computer. There was a literal length limit on how long a parallel cable you could buy for your printer.

Serial was not nearly as fast with signals, but with a serial cable you could have your computer in one room and the printer in another. Considering how noisy those early printers were (they used pin hammers against ink ribbon to make characters*) this was not a bad thing at all. You could put your printer in a room, close the door, and only visit it when you needed to retrieve the printout.

Then as now the serial interface got faster and the parallel cable went the way of the dinosaur.

Your USB cable is really a serial cable. The "S" stands for serial from Universal Serial Bus.

* It sounded like someone cutting sheet metal with a circular saw when it ran.

Why are Watt and Hertz Capitalized?

James Watt: Was a Scottish inventor and engineer who produced one of the first successfully viable steam engines. By no means did he invent the first one, but he did build the first practical, marketable steam engine.

He targeted sales of his engines to farmers and others who worked in agriculture. He also coined the term "horsepower." This wasn't just a frivolous application of a new term. He wanted his potential steam engine customers to be able to easily relate what his engines could do to the common prime mover of the day; the horse.

In fact, Watt got it wrong. By his measure of a horse's power they are not as strong as he gave them credit for. This way his "horsepower" engines actually did better than the actual horse. Or, as some have said, he under promised and over-delivered.

The reason the "W" of Watt is capitalized is out of respect for Mr. Watt.

Heinrich Hertz: The term Hertz refers to the a measure of frequency or "a measurement of the number of times that a repeated event occurs per unit of time." Usually this unit of measurement is applied in seconds, microseconds, and so on.

The reason the "H" of "Hz" is capitalized is again a mark of respect for the person who came up with a standard unit of measure, like Watt, that has a lasting place in terminology.

Could you be the next James Watt or Heinrich Hertz? Why not!


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  • aqeel husssain 8 years ago

    i m happy to see that it is very help for students as well as for all people who keep interest in computers

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