What Are the Different Types of PC Memory?
There are several different types of memory in your computer. The main memory in your computer is physical memory or Random Access Memory (RAM). You can read and write data to RAM and it is found on all computers. In addition, your computer has Read Only Memory (ROM) and cache memory. Virtual memory is found in operating systems and desktops, however, not all computers have virtual memory. Your computer also has storage memory or long term memory in the form of a hard drive, and may have a floppy disk drive.
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History of Computer Memory
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Magnetic drum storage first emerged in 1930 and evolved through the 1940 time frame. It is the predecessor to the hard disk drive. The development of integrated circuit technology began in 1959 when transistors were put onto silicon chips. A 1024-bit memory chip was produced in 1970 and a doubling of memory density on chips continues to this day.
Types of RAM and ROM
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There are three main types of RAM: Synchronous DRAM (SDRAM) runs at 133 MHz up to 180MHz, Double Data Rate SDRAM (DDR) doubles the data rate of SDRAM and Rambus DRAM (RDRAM) serial memory technology with double the data rate of SDRAM with a higher latency or amount of time it takes to get the data from memory.
Your computer has plain old ROM and may have special types of ROM such as: programmable chips that allow you to store a program and are not erasable or reusable, Erasable Programmable (EPROM), which can be erased by exposing it to ultraviolet light, and Electrically Erasable Programmable (EEPROM), which can be erased by exposing it to an electrical charge.
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Function of Memory
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RAM is composed of integrated circuits called chips. Each circuit has millions of storage locations called cells. Cells are made up of a transistor and a capacitor that work together with the assistance of memory controller circuitry to read and write data on your computer. The Central Processing Unit (CPU) on your computer is connected to the memory controller circuitry via wires that are called a BUS. This technology determines the speed data is transmitted between the CPU and the memory controller circuitry in your computer.
Basic ROM contains the critical instructions required to start your computer. ROM memory is stored on chips on your motherboard and cannot be changed, erased or removed. ROM is much slower than RAM.
If your computer RAM becomes full, virtual memory kicks in. Your operating system moves the data and program instructions from RAM to your hard drive and accesses them as needed. It does this via a paging file that is not considered part of your RAM. Virtual memory assists your short term memory in running efficiently.
There are two levels of cache that may be available to your CPU. Level 1, the primary cache, is a small amount of memory made available to support the Central Processing Unit (CPU). It allows easy and fast access to data the CPU uses consistently. Level 2, the secondary cache, resides on a memory card, and the amount of memory depends on the CPU in your computer. An integrated circuit on the motherboard controls the level 2 cache to reduce the time your CPU has to wait for data from main memory.
Misconceptions
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Since RAM stands for random access memory, there is a misconception that ROM is not Random Access. However, random access is defined as the ability to read any location in any order, and you can read from ROM in that manner, you just can't write to it.
Warning
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If you need to upgrade or purchase more memory be aware that there is a difference between laptop and desktop memory, usually the size. Generally, a laptop has 4 memory components, and a desktop has eight memory components.
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