A computer runs on two major types of memory: RAM and memory in the hard drive. The two are necessary to basic computer functions. RAM is short-term, temporary memory, while hard drive memory is long-term and can be permanent.
A hard drive is the storage capacity of the computer, or the long-term memory, and it is sometimes also called "disk space." The storage capacity is usually measured in gigabytes (GB) and is the place where files are saved when a user presses the "save" button on most applications. Inside of the hard drive is a metal disk that spins while a head writes the information onto it.
RAM is sometimes called "memory" for short which further complicates the issue. It is a computer chip that contributes to the speed of the computer, and it is typically measured in megabytes (MB) or gigabytes (GB), depending on the size of the chip. When a user chooses to open a file, the computer must put that information somewhere to be able to access it. It writes the file temporarily to the RAM for easy access, and this type of memory also temporarily saves files that are currently being worked on.
A major difference between RAM and memory on the hard drive is its permanence. Files stored in RAM are sent to the chip by little electrical charges that are necessary to keep the files intact. If the computer is turned off or crashes, the electrical charges stop and the files are lost. Hard drive memory is written onto the disk when a program is "saved," so these files are not lost in the case of a crash or power loss. Computer uses should save their work as it is being written, since every time this is done, the file is rewritten in its new form onto the hard disk.
Another major difference between these types of memory is that RAM can be often be upgraded. Computers have ports on the motherboard to plug RAM chips into, and in many cases, these chips can be easily removed and new ones plugged in. If a user has 32 MB of RAM in her computer divided between two chips, then she has two 16 MB chips. If she purchases two 64 MB chips instead, they can replace the old ones and give her 128 MB of RAM. This small and simple upgrade is relatively inexpensive and can make a huge difference in the speed and performance of a computer, although computers typically can only use certain types of RAM in specific amounts or configurations.
Computer owners typically want to know if they have enough RAM and memory to run a particular program. RAM will be significantly less in numbers than hard drive memory and is typically 128 MB - 1 GB. Since hard drive memory needs the capacity to hold significantly more files, the average capacities range from 1 - 400 GB. Individual programs will list the required RAM and disk space necessary for them to run effectively.