Stevens 1 Lemuel Stevens Kim Younger English 1213, Section 0680, Classification Essay 17 April 2006 A Different Side of Memory A common question many people ask is why computers and other devices need different types of memory? The answer is, as new technologies are introduced in an attempt to match the improvements in the Central Processing Unit (CPU) design, the speed of memory has to somewhat try to keep pace with the CPU, or the memory will become a bottleneck. Computers have gone through immense changes in design; out of giant air-conditioned rooms, into closets, onto desktops, and now are small enough to fit in the pockets of or on the laps of human beings (Null and Lobur 1). First and foremost, the most important component of the computer is its processor. It is considered the heart of the computer that does all the calculating and processing; but with all that calculating and processing, the computer would not be such a remarkable device if not for its amazing memory. Computer memory makes it possible to retain important information on a computer; such data can be used again and again and retrieved when a certain stored data is needed. Without the computer memory, the processor will have no facility where to store its important calculations and processes, thereby making them useless. Although there have been many improvements in CPU’s over the past few years, the race to keep pace with the CPU design has had varying effects on memory architecture, speed, and expense. Today, there are four main categories of memory architecture: Random Access Memory (RAM), Read Only Memory (ROM), Cache Memory, and Virtual Memory.
Stevens 2 RAM is somewhat of a secondary term. More specifically, it should be called read write memory, for that is what it is used for by the computer; to retrieve data and programs currently in use, and then to write data back to memory. It constitutes the working of area of the computer and is also termed main memory for its significant importance to the computer. RAM is the memory to which computer specifications refer; if a person buys a computer with 128 megabytes of memory, it has 128MB of RAM. Hence, the performance of a computer can be significantly improved by including more memory. If there is too little memory, more frequent access to a hard disk is required; this is not good as reading from a hard disk involves a longer time period than reading from RAM. Large main memory enables the system to store all the files needed for an application, hence, reducing the time needed to access files for any application. There is a major drawback to RAM: it is volatile which suggests that the current contents are lost when power is removed or different programs and data are entered. There are generally two types of integrated circuits used to build the bulk of RAM memory in today’s computers: SRAM (Static Random Access Memory), and DRAM (Dynamic Random Access Memory). “Dynamic Ram is constructed of tiny capacitors that leak electricity…[hence it] requires a recharge every few milliseconds to maintain its data” (Null and Lobur 234). Static RAM on the other hand, holds its contents for as long as power is available. Although SRAM may be more expensive than DRAM, DRAM is the better preferred because “more bits can be stored per chip, uses less power and generates less heat than SRAM” (Null and Lobur 234). For these reasons, both types of RAM are often used in combination: DRAM for main memory and, SRAM for cache memory, which is a small amount of super-fast memory located near to the processor for quick retrieval of data and programs.
Stevens 3 In addition to RAM, computers and other devices also make use of ROM (Read Only Memory). ROM is used to store critical information that maybe necessary to operate the operating system in the case of computers or the main processor in other devices. “ROM is not volatile,…always retains its data [, and…] is also used in embedded systems or any systems where the programming does not need to change. Examples of such devices are toys, automobiles, and calculators; these devices have a definite need to retain values even when they are shut off. One other important feature about ROM is that the data written to it cannot be overwritten by other programs or data, hence, the term read only memory. The software contained within ROM is the same for most machines and generally includes part of the BIOS (Basic Input/Output System) as well as special programs and data which have been installed during the process of the computer manufacture (Knott and Waites 91). Just as RAM has two types of chips, so does ROM; however, their definition is more of a categorical type rather than of speed or architectural type. PROM or programmable ROM chips are chips that allow a user to alter the data stored on them, while EPROM or Erasable PROM chips are chips that allow a user to erase the contents of the chip via “exposure to ultra-violet light and then [can] be replaced using a special EPROM programmer device” (Knott and Waites 92). Apart from ROM and RAM, computers today, require another type of memory that is essential for the operating system to run error free. Virtual memory is a common part of most operating systems on desktop computers, and it has become very common because it provides a big benefit for users at a very low cost. Although most computers today are capable of accessing up to 4GB of memory (equivalent of handling a 2 32 integer), operating systems still need access to some other type of memory capable of storing any data and or programs that the RAM in use cannot store. This generally happens whenever a user tries to run multiple software applications,
Stevens 4 and the amount of RAM on that computer, is insufficient for the RAM needed to run those applications simultaneously. If there were no such thing as virtual memory, then once a user filled up the available RAM his/her computer, then the computer would return an error message, forcing the user to take immediate actions. With virtual memory, computers look at RAM for areas that have not been used recently and copy them onto the hard disk. This frees up space in RAM to load the new application. Hence, it is safe to say that virtual memory is interdependent on RAM, and the more RAM a computer has, the more memory will be available for today’s memory-craving applications. Memory is as important to computers as it is to humans. It is organized as a hierarchy with the most important types at the top, and the least important at the bottom or at the very back. In the case of computers, larger memories are slower, and smaller memories are faster but more expensive. However, all types are required for today’s computers as according to Moore’s Law, which states that the density of transistors in an integrated circuit will double every year, one type alone will not be sufficient for handling the many tasks processors will be engaged in. After all memory is the mother of all wisdom. Why not supply devices with as much memory as it can possibly hold?
Stevens 5 Work Cited Knott, Geoffrey, and Knick, Waites. Computing Third Edition. Great Britain: Sunderland, 2002. Null, Linda, and Julia, Lobur. The Essentials of Computer Organization and Architecture. Great Britain: Lobur and Bartlett Pub Int’l, 2003.