This article is aimed at understanding how memory works and what to look for
when buying it. We also take a look at gaming performance on the Pentium 4 platform
and see how different factors such as latency, and frequency can affect it.
We also cover DDR and DDR-II memory.
What is Memory?
In its rawest form, memory is a simply a medium for temporary or permanent
storage of data. Memory is everywhere, in different sizes, styles, speed and
interfaces. Your processor for instance will contain at least two cache memory
areas, your graphics card has perhaps a 256MB frame buffer and most people will
carry a flash memory device of some sort with them, such as a mobile phone.
When assembling a computer, the two most prominent types or memory that we
need to know about, are the hard drive and the system memory. The hard drive
as covered here,
works with a system of spinning platters with the data stored in a magnetic
form. This is a non-volatile medium, so when the power is removed from the device,
the data stays exactly where it is.
The main system memory is used as a temporary storage space and is volatile.
This means that when the computer is switched off, all data is lost. This is
one of many reasons why giving Windows a reboot can solve issues, as everything
has to be reloaded.
In Windows, you may notice what is referred to as a swap file or virtual memory.
This is where the computer extends its system memory into an allocated space
on your hard drive. This is a last resort as the hard drive is much slower than
the system memory and can have a huge impact on performance. Similarly, the
Level 2 cache which is next up in the hierarchy from system memory is even faster
and comparatively more expensive.
How does memory work?
Data is stored in bits, which are the simplest form of data possible. They
make up the digital era that we are surrounded by. A bit is only ever a 1 or
0, sometimes written as on or off, high or low. Using a sequence of 8 bits,
you can make a byte. A byte can therefore give you an 8-Bit number, which is
2^8 or a range of 0-255. This number could represent anything from a colour
value in a picture, to an ASCII code for text. The normal rules then apply,
with 1024 bytes making a Kilobyte (KB), 1024 Kilobytes making a Megabyte (MB)
and 1024 Megabytes making a Gigabyte (GB).
Be sure not to confuse bits and bytes. For instance you might see something
written as 11Mb. Because of the lower case 'b', this means Megabit, not Megabyte - an easy trap to fall into.
Considering most memory modules are now 512MB, you can imagine there are a
lot of these 1bit cells. System memory is based on DRAM (Dynamic Random Access
Memory), which is cheaper to make than SRAM, which is mainly used in cache.
The further down the memory tier system you go, the slower and cheaper memory
gets, with hard drives being the cheapest per megabyte.
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