Internal hard disks Speed: Very fast! The speed of a hard disk is often quoted as "average access time" speed, measured in milliseconds. The smaller this number the faster the disk. There are different types of disk, and commonly used types are known as EIDE and SCSI drives. SCSI is better for large network servers while EIDE drives are often better for desktop computers.In 2009 SATA drives became common, they're faster than the EIDE drives. All these Hard Drives now look like being replaced by Solid State Hard Drves ( Similar to memory sticks in principle but with large capacities.) Hard Drive capacities in 2009 are now getting into the Tetrabyte (1000 Gigabyte) Gigabyte is equivalent to 1024 Megabytes. Hard disk costs are falling rapidly and normally represent the cheapest way of storing data.
External hard disks Speed: Normally slower that internal disks, but more expensive versions offer the same performance as internal hard disks.Capacity: Same as internal disks.Cost: More expensive than internal disks.
USB sticks (memory sticks) Speed: Very slow!Capacity: Normally 1.44 Mbytes.Cost: Now hard to get hold of - redundant system.
CD-ROM Disks Speed: Much slower than hard disks. The original CD-ROM speciation is now given a value of 1x speed, and later, faster CD-ROMs are quoted as a multiple of this value. Thus, a 50x CD-ROM is 50 times as fast as the original 1x speed CD-ROM specification.Capacity: Around 650 Mbytes.
CDRW -
the record and playback of these units is becoming
much faster- 2002 - a typical unit for under £50 is 40x12x48 where
40 is the max write speed for CDR ( these can be recorded on only once)
12 is the max speed for writing on CDRW (Re- recordable CDs) and 48 is
the read speed.
DVD Drives Speed: Much faster than CD-ROM drives but not as fast as hard disks.Capacity: up to 17 Gbytes.Cost: Slightly higher than CD-ROM drives. DVDRW are now the latest addition to the range
Internal hard disks are located inside your main computer unit, while external hard disks are joined to the main computer unit via a lead that you plug into the back of your computer unit.
Tape Storage- used mainly for backups -they have a large storage capacity but access to the individual data is slow and not area seek specific as in the disks which perform file location at high speed.
2009 - USB Memory Sticks (A type of flash memory) are now in common usage. They're produced in ever increasing capacities in 2009 1Gb to 32Gb increasing. They're very fast for storage and files are easily erased and replaced.