It used to simple to answer the question, “how fast is my computer?” You just looked at how many megahertz (MHz) a computer had. But these days computers have multiple cores, 64-bit processors, alternative types of RAM, fancy hard drives, and giant caches. Figuring out your computer’s speed relative to other computers requires a degree in calculus.
I can’t change that, but I can tell you how each part of your computer contributes to its total overall speed so you can make a rough estimate of your computer’s true speed.
Doing Math Billions Of Times A Second
In a normal computer, the chief indicator of overall speed is the speed of your Computer Processing Unit (CPU), which is usually indicated in megahertz (MHz) or gigahertz (GHz). Hertz is a term that means “per second.” Mega means million and giga means billion, so here are the technical definitions of MHz and GHz:
- Megahertz: millions of times per second
- Gigahertz: billions of times per second
So what exactly in your computer is happening millions or billions of times per second? Computer scientist call it a cycle.
During each cycle, your CPU can do one thing or one predefined set of things, called an operation or an op. For example it can add (combine) one plus one and get the answer, two. It can also do a whole bunch of other things, but almost all of them are very simple.
Yet, doing simple things millions or billions of times a second adds up quickly. It takes thousands of simple operations for your computer to open the Start menu, but even 10,000 operations takes a 2 GHz CPU only 1/20,000th of a second.
But don’t be fooled: computers with higher CPU speeds—called clock speeds—aren’t necessarily faster than other computers. There are other things that speed up your computer because your CPU doesn’t work alone.
How Memory Affects Your Computer
CPUs work at incredible speeds, but they’re worthless unless you can give them useful work. That’s where computer memory applies.
There are three types of computer memory on your computer, although we typically only use the term “memory” for one of them. They are:
- Cached memory: this is memory that sits on or near the CPU so the CPU can access it quickly. It typically runs at the same speed as the CPU.
- Random Access Memory (RAM) which is what we usually call “computer memory”. This sits further away from the CPU and runs at a speed half to four times as slow as the CPU. However, you can usually have hundreds or thousands of times as much RAM as you can have cache.
- Persistent memory, this is the data stored on your hard drive. Even the best hard drives run millions of times slower than your CPU.
How your computer combines these three types of memory can help you answer the question, “how fast is my computer?”
When considering speed, each of these different memory types counts differently.
- The more cache you have, the faster your computer will be (up until a point). Typical cache sizes go from 8 megabytes to 128 megabytes. Unfortunately, you can’t add more cache to your computer without buying a new CPU.
- RAM counts twice towards your speed. First there’s the speed of your RAM, usually measured in MHz. The closer the speed of your RAM to the speed of your processor, the more efficient your computer can be and the less it matters how many megabytes are in your CPU cache. Second, there’s the amount of RAM you have—the more RAM you have, the more data you can keep in RAM instead of on a slow hard drive. See how to upgrade your Computer memory.
- Persistent memory, hard drives, are best tracked by their seek time and throughput. Seek time is how fast they can move from one part of the drive to the next. Throughput is the maximum amount of data they can transfer at a time. Standard magnetic hard drives have relatively high seek times (bad) and high throughput (good). Newer solid state drives have practically zero seek time (great!) but variable throughput depending on device quality and situations.
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Two Other CPU Features Which Affect Your Speed
You’ve probably heard about CPU cores and 64-bit computing. In some cases, these can give you an amazing speed boost, but it many cases they fall far short of their potential. Let’s look at the good news first.
Your computer thinks in bits—a single switch which can be either on or off. Computer scientists represent it as a zero (off) or a one (on).
(Nifty fact: look at the power button on your computer. It probably looks like a zero with a one sticking out of it—that’s the ISO symbol for “on/off”. The ISO symbol for “on” is a one and the symbol for “off” is, you guessed it, a zero.)
Of course, there’s not much you can do with just one bit, so your computer thinks in multiple bits at a time. Really old computers used to think in 8 bits at a time. Then they got to 16 bits and finally 32 bits. That’s where the Personal Computer (PC) revolution took off and we got stuck at 32 bits for a long time.
The problem is that software written for a 32-bit processor won’t run automatically on a processor with more bits. But finally Intel and AMD worked around that problem earlier this decade and we started to get 64-bit processors.
Now 64 bits might sound like a minor improvement, but it’s more than that in a sense. You can think of the number of bits as the number of digits a number can have. Is 1000 twice as large as 10 because it has twice as many digits? Of course not. So neither is 64 bits twice as large as 32 bits. It’s actually a billion times a billion times as large.
That’s the great news—and you can see why people really pushed for 64-bit computers. The bad news is that people—and even computers—rarely need to do math with numbers so large that we don’t even have words for them, so 99% of the time your computer doesn’t use its extra bits.
The good news in the bad news is that there are a few applications, mostly scientific and database-oriented, which can use those extra digits to get extra speed.
The other part of your CPU which looks great on paper but which isn’t necessarily so is multiple cores. In theory, each core is its own CPU, so every time your double your cores, you double your speed.
The bad news is that most programs aren’t very good at taking advantage of multiple CPUs. In order to use multiple CPUs, you need to split your work up into chunks—and then you can’t continue until all of the chunks come back. It’s kind of like going to a restaurant with a large group when you’re hungry—you can’t politely order until everyone is ready, and the longer you wait to order, the longer it takes to get your meal.
Multiple cores still do help a lot, but unless you have a several separate programs running at the same time, you’ll never get four times as much speed from four times as many cores.
A few other things can affect your computer, such as its temperature (cooler is better) and its bus speed (measured in MHz, faster is better), but the elements covered above will answer 99% of the question, “how fast is my computer?”