Memory and hard disks
There is often some confusion when people talk about memory and hard disks. These things simply get mixed up, although they are not the same.
- Memory is Random Access Memory (RAM) - a place where operating systems (such as Windows XP, Windows Vista, Ubuntu Linux) and programs keep their most used files temporarily while working. Memory is always completely erased when you turn off or restart your computer.
Memory size is usually from about 512 megabytes to 8 or more gigabytes.
Common memory types are SDRAM and DDR SDRAM.
You can check the total amount of RAM installed in your PC using keyboard shortcut Windows Key+Pause/Break. This opens System Properties window.
- Hard disk is Hard Disk Drive (HDD) - a place where your files (documents, pictures, videos, etc), plus operating system and program files are stored. Hard disk contents do not get erased when you restart or turn off your computer.
Hard disk sizes usually range between 80 gigabytes and 1 terabyte or more.
Common hard disk interface types are PATA (aka ATA), SATA, SAS and SCSI.
All hard disks have at least one partition (aka volume) - this is where your files are stored. When you open My Computer in Windows XP, Vista or 7, each usable hard disk partition is called "Local Disk" (unless a label has been set) and has a drive letter ("C:" to "Z:"; "A:" is reserved for floppy disk drives) assigned to it - for example, "Local Disk (C:)" or "Local Disk (D:)". If a label has been set for the drive, use Details view or open drive properties to see if the drive is Local Disk, Network Drive or Removable Drive. Details view also reveals drive sizes.
Here's Windows XP's My Computer in Details view, where Type column displays drive type.
To put it simple - memory (RAM) is a temporary and hard disk is a permanent place for files.
Let's illustrate hard disk and memory differences with a photo.
From the left is a desktop computer hard drive (PATA interface) and a common laptop computer hard drive (also PATA interface). Notice the size difference - laptop hard drive is much smaller to fit in a laptop or netbook. This often means that laptop hard drives are slower because they have to be small and energy-efficient.
From the top right there is a common desktop computer memory module (DDR2) and a common laptop computer memory module (also DDR2). Again, laptop memory module is only half the size and therefore often slower.
When someone asks you "How much free space you've got?" then it means how much free space your hard disk has. Never say something like "I've got 100 gigabytes of free memory". You've got 100 gigabytes of free disk space, not memory.
Why not use just hard disk for everything, what's the use of temporary memory?
Well, memory works hundreds to thousands of times faster than a hard disk, and it has no moving mechanical parts. Therefore it is better to keep most often used things in random access memory for very quick access.
This also means that the more RAM your computer has, the better it performs. Windows Vista and 7 users are able to take advantage of ReadyBoost service that speeds up computers using USB flash drives and memory cards - but the service is still not as good as adding more RAM.
Opening a computer case and adding or replacing memory modules or hard disks is a job for people who know what they are doing. If you are not common with these, do not try to do everything yourself - you might end up with a broken computer. Call a specialist instead.
You still need some information before buying memory modules or hard drives.
For memory modules, you need to know the name (type and speed), for example, DDR2-3200 or DDR3-10600 (aka PC2-3200 or PC3-10600) and whether there are any available memory slots in your computer.
For hard disk drives, you need to know interface type, for example SATA or PATA.
Luckily, there is a free program to help you with this - Speccy. Head to its download page and click the Download from Piriform.com link.
After downloading and launching the installer, Speccy setup starts by asking for the language. As English is fine, click OK.
Click Next in the absolutely useful Welcome screen:
As no one really reads (understands) a License Agreement, click I Agree: You can also grab several headache pills and really read it thoroughly before clicking... if you feel an unstoppable urge to do so.
Clear the Add Desktop Shortcut check box (you do not need Speccy that often!) and click Next:
Then, another useless offer appears - it might be free Google Toolbar, Google Chrome or anything else. Remember, you do not need all the software in the world on your computer and that too many programs tend to slow computers down!
Clear the Install the free Google Toolbar along with Speccy box (or any other check boxes) and then click Install:
After the setup is complete, click Finish. This will also run Speccy right away.
Oh yes, Windows Vista and 7 users will encounter a warm and caring touch of User Account Control before actually running Speccy. Click Continue or Yes in the dialog.
It takes a few seconds for Speccy to gather system information. After the process is complete, an overview appears.
To see information about memory modules, click RAM either on the left side or in the overview part.
You will then see detailed information about the memory modules and slots on your computer.
Memory slots section shows how many total, used and free memory module slots there are on your computer.
In the example below, there are no free memory slots. This means that adding memory requires purchasing two new memory modules. Why two? Because Memory type is DDR3 and all DDR memory modules work faster if they are installed in pairs of same size and speed (Dual Channel mode). So in this case, if you want to upgrade RAM size from 4 GB (2x 2 GB modules) to 8 GB, you should buy two identical 4 GB DDR3 modules. This affects only DDR, DDR2 and DDR3 memory types, SDRAM, EDO and other types of memory modules can also be added one module at a time.
If your computer has free memory slots, fill them with smaller modules instead (for example, additional two 2 GB DDR modules).
Memory type is DDR3 here. This is often called PC3, too. Respectively, DDR2 is called PC2 and DDR is called just PC - i.e PC3-6400, PC2-3200 or PC-1600.
Memory size is quite strangely 3952 MBytes (3.952 GB) in the example below. This really means that the computer has 4096 MB or 4 GB of memory installed and some memory is dedicated to a graphics card. Always round strange numbers up to find out the real amount of memory.
Please remember that 32-bit Windows XP, Vista and 7 are unable to use more memory than 4 GB, so there is no point in adding more RAM for those! Memory sizes over 4 gigabytes come handy only on 64-bit Windows. To see if you have 32- or 64-bit Windows, open Speccy Summary page from the top left.
DRAM Frequency is important for finding out the peak transfer rate (and module name) of memory. Computer shops label memory modules something like DDR3-8500 (or PC3-8500) and DDR2-6400 (PC2-6400). The frequency must be converted to the peak transfer rate to find the correct modules easily. See the conversion tables in the article for this. Nevermind if tables have specified numbers a little different - 532 MHz here still means 533 MHz.
Next items, CL, tRCD, tRP and tRAS have also a lot to do with memory speed, but let's not get more technical than this, right? Simply, the lower the numbers are, the faster the memory modules work.
DDR3 SDRAM Frequencies and corresponding Module Names:
400 MHz = PC3-6400
533 MHz = PC3-8500
667 MHz = PC3-10600
800 MHz = PC3-12800
933 MHz = PC3-14900
1066 MHz = PC3-17000
DDR2 SDRAM Frequencies and corresponding Module Names:
200 MHz = PC2-3200
266 MHz = PC2-4200 or PC2-4300
333 MHz = PC2-5300 or PC2-5400
400 MHz = PC2-6400
533 MHz = PC2-8500 or PC2-8600
DDR SDRAM Frequencies and corresponding Module Names:
200 MHz = PC-1600
266 MHz = PC-2100
333 MHz = PC-2700
400 MHz = PC-3200
To sum up - following the same example, you need to buy two 4GB modules with names PC3-8500 or DDR3-8500.
Whew, was that too technical? Consult some IT specialist if the lines above made no sense.
If you add more memory to your computer, you might need to adjust page file size in Windows. By default, Windows resizes paging file itself, but many users set the file to a fixed size to avoid possible fragmentation and performance issues.
To find out which interface type your hard disk has, click Hard Disk on the left.
Here, only two lines are really important - Interface and SATA (or PATA) type. In the following example, the SATA type is SATA-II. For SCSI, there is no SCSI type line shown. That's all you need to say in the shop - for example, SATA-II hard disk drive. Also specify if you need the hard disk drive for laptop or desktop computer. And specify the needed size (the Real size field), too!