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Posted on Apr 27, 2010 in Backup, Planning A Backup | 0 comments

Understanding backup and computer storage

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If you’ve been struggling to understand our articles on backup and particularly full disk backup, this page will help you understand the concepts a little better.

Memory sticks

RAM sticks, fast enough for primary storage

Primary Vs Secondary storage

Computers use two different types of storage when running Windows or any other modern operating system. When people talk about how much ‘memory’ your computer has, they are referring to RAM (random access memory). RAM is primary storage. Primary storage is used for the programs and data the computer is currently working on. Secondary storage includes hard drives, CD and DVD ROM discs, USB drives, floppy disks and ROM (read only memory) chips.

Why do computers need two types of storage? RAM is very fast to access and therefore ideal for primary storage. However, when the power is turned off all the contents of RAM are lost. RAM is also much more expensive than any secondary storage media. Secondary storage simply is not fast enough to store information that the computer is currently processing however.

Role reversals

Amiga RAM disk

Because of the speed of RAM compared to hard drives, some innovative hardware has in the past toyed with the idea of using RAM as a secondary storage medium. The once popular Amiga line of desktop computers let users use any free RAM as if it was an attached disk drive. Of course the contents of the disk were destroyed when the power was turned off.

More recently, the Gigabyte i-RAM expansion card used RAM chips and a battery backup to create a blazingly fast hard drive.

Sometimes things go the other way around too. You may have heard of virtual memory. This is an area on your hard drive that is used as if it were primary storage. Windows intelligently uses this space as a last resort if it runs short of memory since accessing it will dramatically slow down the computer.

Memory (RAM) and hard disk capacity are typically measured in Gigabytes. A Gigabyte (often written GB) is 8,589,934,592 bits (although confusingly, some manufactures measure them slightly differently). In real world terms, that is about an hour of standard definition video or 114 minutes of uncompressed CD audio (remember the audio you listen to on your Mp3 player is compressed). To buy 1 GB of RAM will cost you at least $20 in March 2010, by comparison you could buy a hard drive of around 80 GB for around the same price.

So, you now understand the two types of storage in your computer. When you first turn your computer on the primary storage is blank. Luckily your computers processor knows where to look for its first instruction. It then reads from a ROM chip which tells it how to load Windows (or whichever operating system is stored on your hard drive). Without the hard drive, there’s not much you can do with your computer which is why it is important to have some kind of disaster recovery plan and that is where disk backup programs can help.

Jargon busters

It is hard to talk about backup software without using some technical terms. Below, we will try to explain any terms which you may not be familiar with:-

AES – Short for Advanced Encryption Standard. AES is a tried and tested encryption standard that is trusted by governments and big businesses. Backup programs which offer AES encryption can protect potentially sensitive information stored in the backups they create, assuming the AES encryption is implemented correctly.

Bootable USB flash drive – For computers that do not have a CD or DVD ROM it is possible to use a USB flash drive/pen drive as an alternative (see also Rescue CD).

Boot/booting – The process in which your computer starts an operating system when you first turn it on. This could be Windows or the operating system on a rescue CD or USB flash drive. The term is derived from bootstrap which, according to Wikipedia, “began as a metaphor derived from pull straps sewn onto the backs of leather boots with which a person could pull on their boots without outside help”.

Chkdsk – This is a standard Windows program which checks the contents of disks attached to your computer for consistency and for errors. Click here to view a tutorial on Chkdsk.

CRC – Abbreviation of Cyclic Redundancy Check. A method of testing computer data to detect changes or corruption that happened during transmission or copying.

Disk imaging – The process of copying all the information from a hard drive (or other secondary storage medium) into a file or files which can be stored as a backup.

Disk sector editor – A tool which can inspect and edit the contents of hard drive sectors, rarely used outside of computer research laboratories.

File level backup – Refers to backing up individual files or folders rather than the whole hard drive.

Hot Swap – Storage devices that can be hot-swapped can be safely removed from the computer system without first powering it down.

Imaging – See Disk imaging.

Incremental imaging – Software which performs incremental imaging will save only the information that has changed since the last image backup was created. This can significantly reduce the amout of storage space required for regular image backups.

Master boot record – A crucial piece of information on a hard drive or other secondary storage medium which tells the computer how to load the operating system on the disk. Often abbreviated as MBR.

MBR – See Master boot record.

Mount image file/mounting an image file – Because it is often inconvenient to record an image file back to a physical hard drive, many backup packages support mounting an image file. When an image file is mounted, the backup software makes it available to Windows Explorer just as if it were a real hard drive attached to the computer. The user can then explore and search the contents of the image file and extract files and folders as necessary. Note that it is not normally possible to write to the mounted image file. (See also Disk imaging)

Partition – Storage space on hard drives can be partitioned or split into different sections. These sections, although on the same physical hard drive, appear as distinct devices when using Windows. Care must be taken when choosing a backup destination as storing a backup copy of a drive onto a partition on the same physical drive will not provide protection against hard drive failure.

Rescue CD – Rescue CD’s are used when Windows cannot be started for whatever reason. Instead of booting from your computers hard drive, the rescue CD is used instead. This will start a custom operating system that allows the user to restore from a hard drive image or perform diagnostic tasks.

SATA – Short for Serial ATA, this is a technology used for connecting hard drives and other secondary storage devices to a computer.

Shadow copy – A software technology that allows files that are currently in use to be backed up, allowing backup to proceed even when the computer is in use.

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