Memory

Memory

Lets look at computer memory first.  The function of storage in a computer comes in many different sizes, types and shapes.  However there are two basic categories: short-term and long-term.  A typical computer contains numerous types of memory including RAM, ROM, virtual, cache, and various long-term storage devices.  Each type of computer memory serves a specific function and purpose.

Computer memory is measured in bytes.  A single byte is made up of a series of 1's and 0's normally traveling in pairs of eight.  These eight 0's and 1's are the way the computer communicates and stores information.  With each keystroke or character a byte of memory is used.  In another article you will learn more about bits and how the computer thinks.

Measuring Memory

Term/Byte	Abbreviation	Value
Bit	none	0 or 1
Byte	B	8 bits  -example: 00100101
Kilo	K, KB	1,024 bytes
Mega	M, MB, Meg	1,048,576 bytes (Million)
Giga	G, GB, Giga	1,073,741,824 bytes (Billion)
Tera	T, TB, Tera	1,099,511,628,000 bytes (Trillion)

Here is another way of looking at the measurement of memory:
Measuring Bytes

8 bits = 1 byte 1000 bytes = 1 kilobyte 1000 kilobytes = 1 megabyte 1000 megabytes = 1 gigabyte 1000 gigabytes = 1 terabyte

ROM
ROM, or read-only memory is permanent, long-term, nonvolatile memory.  Nonvolatile means is doesn't disappear when the computer is shut off.  It also can not be erased or changed in anyway.  However there are types of ROM called PROM that can be altered.  The P stands for programmable.  ROM's purpose is to store the basic input/output system (BIOS) that controls the start-up, or boot process.

RAM
RAM, or random-access memory unlike ROM works only when the computer is turned on.  This memory is vital to the computer because it controls the moment by moment processes of the computer.  The first thing that goes into RAM is the OS (operating system) which is most cases is Windows 95.  Next for the RAM might be a game, or the Internet browser, or some type of software that you want to use.

Early personal computer only needed about 64K of RAM.  Today that number is drastically higher.  With photos, sounds, and even movies going into RAM, the amount need is now in the millions.  The computer I am currently using has 80 MB or 80,000K of RAM.

Multitasking has put more demand on RAM in the past few years.  Multitasking is the ability to run more than one program at the same time.  For instance, many people like to run Netscape Communicator along with their word processing software.  This means you need lots of RAM to hold both programs.

Other types of temporary memory are cache (pronounced "cash") and virtual memory.  Both of these types of memory supplement the computer's primary RAM and perform the same function as RAM.

Storage Devices:

RAM and ROM may be very important parts of the computer; however, without storage devices like hard drives and disk drives your computer would not be near as useful.

Here are the most common forms of Storage Devices found on your home computer:
 

Thumb Drive or Memory Stick	Hard disk (drive) or HD
A device that in 1998 IBM introduced and has caught on very quickly as a great portable storage device.  It quickly replaced the floppy disk. This small device is extremely reliable and fits in the USB port on your computer.  It come in sizes ranging from 1 GB to 64 GB in size.	A stack of round metal platters called disks encased in a metal air tight shell.  They commonly range in sizes from 60  to 500 gigabytes (1000MB=1GB).  The hard drive's function is to store all the files, and software the computer will ever use.  Any file or software program used by RAM most likely will come from the disk drive.
CD-ROM (Compact disk, read-only memory)	DVD-ROM (digital video disk, read-only memory)
CD's function much like hard drive in that they store large amounts of memory.  What separates them is their mobility and optical storage technology.  Their storage capacity is also very limited compared to hard drives.  The can only hold up to approximately 650 MB of information.  The other big difference is that you have to have a special drive to write to CD's.  Otherwise they can only be read from.	DVD's are similar to CD in that they are written and read by laser.  Hard drives use magnetic currents store data.  However CD's and DVD's use light (laser) to write and read data on a disk.  These long and short pits are then stored or etched on the surface of the disk.  They can only be read by laser technology.  The new DVD technology increased the amount of memory a regular CD can hold.  DVD's can range in sizes from 4.34GB (1000MB=1GB)  to 7.95GB.