Random Access Memory

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RAM, also known as primary storage or main memory, is where the CPU and applications store information and instructions for future use. RAM is considered volatile memory. Volatile memory loses all its stored information when it is disconnected from its power source. In other words, when you turn off the computer, you lose all the information stored in RAM. For example, if you are entering data into a document and suddenly experience loss of power to the system, you will lose the information you have entered into the document unless it has been saved to a permanent storage location, such as the hard disk, CD-ROM, Zip disk, or floppy disk.

The CPU uses unique locations of RAM, called memory addresses, to store information. Memory addresses vary in size depending on how much RAM is available in the system. The CPU can store and retrieve information from specific memory addresses in a random or direct fashion.

RAM Speed

RAM access speed is measured in nanoseconds (ns, or billionths of a second). Older computers operated with RAM access speeds that ranged from 80ns to 120ns. Today it is common to find RAM access speeds of 50ns and faster. Memory speeds can vary greatly, depending on the type of memory being used. In fact, memory such as Synchronous Dynamic Random Access Memory (SDRAM) is measured in megahertz, not nanoseconds. You can determine the access speed of memory by looking at the last printed number on most DRAM chips; for example, BAC4G302H-05 means the access speed is 50ns. An important consideration when installing new memory in a system is to match the speed of the memory to the speed of the motherboard's bus.

Note 

For the test, it is important to remember that the RAM speed is faster in nanoseconds as the number decreases-that is, 6ns is faster than 10ns.

RAM Size

The smallest unit of information measured in a computer system is a bit. A bit is represented in electronic computer terms as a (binary) 0 or 1. There are 8 bits in 1 byte. (See Chapter 5 for more information on binary conversion.)

RAM size and storage capacity are measured in multiples of bytes known as megabytes, gigabytes, and terabytes. Table 4.1 will assist you with RAM units of measure.

Table 4.1: RAM Units and Sizes

Unite Measured	Size of Unit
Bit	Binary digit equal to 0 or 1
Byte	8 bits
Kilobyte	1024 bytes
Megabyte	1,048,576 bytes
Gigabyte	1,073,741,824 bytes
Terabyte	1,099,511,627,776 bytes

Some important considerations when purchasing memory or a new computer are what type of memory and how much memory will be needed. Specific types of memory serve different functions (memory types are discussed later in this chapter). For most home and office workstations, 128MB of RAM should be sufficient to support most of today's memory-hungry applications. High-end server computers require more memory to process, calculate, and serve applications to workstations. Server computers today generally have at least 1GB of RAM installed.

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