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 | Introduction |
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| Types |
| Memory is also called RAM, or Random Access Memory. The main types of RAM are: 1) FPDRAM - Fast Page Dynamic RAM, 2) EDO - Extended Data Out, and 3) SDRAM - Synchronous Dynamic RAM. Fast Page RAM is the original type of RAM used in computers up until the Pentium. Typical memory access time was 100 ns (nanoseconds). EDO RAM was introduced with the Pentium class of computers, but was short-lived. The advantage of EDO RAM was that it had faster read / write (access) times than Fast Page RAM. Typical access times were 70, 60, and 50 ns. The smaller the number, the faster the access time, and the more desirable it is for fast computing. Not all computers that use EDO RAM could use the same speed of EDO RAM. Some computers could only use 70 ns chips. SDRAM was introduced with the Pentium II and has the fastest memory access times at 9 nsec. The three types of RAM are not compatible with all motherboards. Each motherboard can only use one specified type of RAM. The amount of RAM on any given motherboard is limited by the motherboard's memory controller, which is specified by the manufacturer. Putting more RAM on a motherboard means that only the maximum amount of memory the motherboards can use will be used. The rest of the memory will not be used. |
| Functionality |
| RAM is the memory in which the CPU uses to access and store binary data. Unlike stored memory, or storage, like a hard drive, RAM is volatile memory and not considered storage. That is, when you shut the computer off, the data stored in RAM is lost and must be reloaded from a storage device, such as ROM, a hard drive, or any other type of long term data storage device. To illustrate this principal, insert a floppy disk into the floppy drive and load a file into the computer. Do this by selecting the file and clicking 'Open', or by launching an application and then, from there,opening the file. Now eject the floppy disk and run the file. As you can see the data storage device was not needed to execute, or run, the file. This is possible because a copy of the binary file has been loaded into the RAM. The CPU accesses and stores its working data in the RAM. Only when a 'Save' command is executed, or ran, does the computer make a copy of the binary file in the RAM to a desired data storage peripheral. |
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| Data Transfer |
| Computer data is in binary form, which is a series of 1's and 0's. The smallest piece of data is called a bit (a 1 or a 0). The working data piece is 8 bits, which equals one byte. Information in memory is stored in arrays of bytes. These arrays are called shift registers. Shift registers are used throughout the computer architecture wherever data is stored or manipulated. The following applet shows how data is transferred between shift registers in any two parts of a computer. For example, data can be transferred between the memory and CPU. The two main ways data is moved is either serially or in parallel. Serial data transfer is usually piped through a single line one bit at a time from one register to another. Parallel data transfer requires a 'bus' or group of serial lines running from one register to another, which are paralleling one another. The difference is that, in parallel, in one clock pulse all bits from one register move into the other by piping each bit through its own path to the next register. In serial data transfer, data 'shifts' throughout the shift register until each bit is in its corresponding place. This takes eight clock pulses. An example of a serial line is a network. An example of parallel data transfer is found on the bus between the RAM and the CPU. |
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| 8 bit Shift Register
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RAM Guide
The Ultimate Memory Guide (Requires Acrobat Reader
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