Types of Memory
CPUs need quick and easy access to large amounts of data in order to maximize their performance.
If the CPU cannot get to the data it needs, it literally stops and waits for it.
Modern CPUs running at speeds of about 1 higher can consume massive amounts of data -- potentially billions of bytes per second.
The problem that computer designers face is that memory that can keep up with a 1-gigahertz CPU is extremely expensive .
The cost problem has been solved by using expensive memory in small quantities and then backing it up with larger quantities of less expensive memory.
virtual memory .
Because storage space on a hard disk is so cheap and plentiful, it forms the final stage of a CPUs memory hierarchy, called virtual memory
System RAM
System RAM speed is controlled by bus width and bus speed. Bus width refers to the number of bits that can be sent to the CPU simultaneously, and bus speed refers to the number of times a group of bits can be sent each second. A bus cycle occurs every time data travels from memory to the CPU.
Simply changing the bus width from 16 bits to 32 bits and the speed from 66 MHz to 100 MHz allows for three times as much data (400 million bytes versus 132 million bytes) to pass through to the CPU every second.
A particular type of RAM, static random access memory (SRAM), is used primarily for cache.
SRAM uses multiple transistors, typically four to six, for each memory cell. It has an external gate array that switches, or flip-flops, between two states.
This means that it does not have to be continually refreshed like DRAM. Each cell will maintain its data as long as it has power.
Without the need for constant refreshing, SRAM can operate extremely quickly. But the complexity of each cell make it prohibitively expensive for use as standard RAM.
Today RAM is cheap. It's the temporary space the OS and the application use to really do the computing.
The programs you run AND the OS need space to exist when they run (since the don't RUN or execute on the hard drive).
New systems will usually have 128MegaBytes (mb) or 256Mb of RAM. Used systems may only have 32Mb or 64Mb.