Introduction
In the computing world, memory refers to the computer hardware devices used to store data and information for direct use in a computer; it has the same meaning with the term “primary storage” (Computer Memory, 2015). Computer memory, for example random-access memory (RAM), works at a high speed, as a differentiate from storage that provides slow-to-access program and data storage however offers higher capacities. The contents of the computer memory can be transferred to secondary storage through a memory management technique called “virtual memory” if necessary (Tyson, n.d.). The word “memory”, which mean “primary storage” or “main memory”, is often associated with addressable semiconductor memory (What are the differences between Primary and Secondary Memory?, n.d.). Semiconductor memory can be separated into two main kinds, which are volatile and non-volatile. Volatile memory refers to the primary storage, while non-volatile memory refers to secondary storage (What are the differences between Primary and Secondary Memory?, n.d.). Primary storage is a working storage of the computer and it is faster than secondary storage. However it has limited capacity and data is lost when power is switched off as it only holds data or when the computer is on (Computer Memory, 2015). Secondary storage on the other hand is slower than main memory as they store data and information permanently (Computer Memory, 2015) .
RAM
RAM is the primary storage which stands for random access memory (RAM) due to the random selection of memory locations . This type of memory performs both read and write operations on memory (Computer Memory, 2015). In RAM, information is located in a state of thousands of electronic circuits or capacitors. This composition allows RAM to access information speeds up to 3,200 megabytes per second. However, if there is a power failure happening in any systems during memory access, you will lose your data permanently. RAM is categorized into the following types: dynamic random-access memory (DRAM), static random-access memory (SRAM), and synchronous dynamic random-access memory (SDRAM).
DRAM
Dynamic random-access memory (DRAM) is one of the random-access memory that stores each bit of data in a separate capacitor within an integrated circuit (Rouse, n.d.) . The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1 (Rouse, n.d.) . It is widely used in digital electronics where low-cost and high-capacity memory is required. The main memory in modern computers is one of the largest applications for DRAM; and as the major memories of elements used in these computers. DRAM has the advantage of its structural simplicity which means only one transistor and a capacitor are required per bit, compared to four or six transistors in that of SRAM. This allows DRAM to reach very high densities (Rouse, n.d.) .
SRAM
Static random-access memory (static RAM or SRAM) is a type of semiconductor memory (Rouse, n.d.-c) . SRAM is different from DRAM which require computer user to refresh it periodically. SRAM is faster and more expensive than DRAM, it is typically used for CPU cache while DRAM is used for a computer’s main memory (Rouse, n.d.-c).
SDRAM
SDRAM is a change to improve the standard DRAM since it recovers information on the other hand between two arrangements of memory (Rouse, n.d.-c) . It is called “Synchronous” DRAM because the memory is synchronized with the clock speed that the computer’s CPU bus speed is advanced for (SDRAM, n.d.). The speed of SDRAM increases according to the processors bus speed. The speed of SDRAM is measured in Megahertz, which makes it simple to contrast the processor’s bus speed to the speed of the memory (SDRAM, n.d.)
Cache
Another form of memory is cache memory (pronounced cash). The speed of CPU is very high when compared to the access time of main memory. Therefore the performance of CPU will decrease because of the slow speed of main memory. To minimize the mismatch in operating speed, a small memory chip is attached between CPU and main memory whose access time is very close to the processing speed of CPU (Computer Memory, 2015) . Cache memories are accessed much faster than conventional RAM. It is used to store programs or data currently being imposed or not permanently data frequently used by the CPU. It is highly expensive to have a bigger size of cache memory and its size is normally kept small (Computer Memory, 2015) . Cache memory acts as a buffer between the CPU and main memory (Computer – Memory, n.d.). It is used to hold those parts of information and program which are constantly used by CPU. The parts of data and programs can be transferred from disk to cache memory using the operating system, where it is accessible to the CPU (Computer – Memory, n.d.). The cache memory is categorized into levels (Tyson, n.d.). For level 1, cache is part of the microprocessor, it can holds 8 to 256 KB. In level 2, cache is known as external cache, it can holds 64 kb to 2 MB. Up to level 3, cache is known as the motherboard. It comes on very high-end computers and can holds 2 to 8MB (Tyson, n.d.).
Hard Disks
Hard disks is a type of memory which is thin, rigid metal, glass, or ceramic platters covered with a substance that allows data to be held in the form of magnetized spots. This is where you store documents, music, games and other files while you are not using them. Hard drives work like a record as the inside of the hard disk there is a spinning platter, and an arm with a “head” that touches different parts of the platter to read from or write to them (Vertesi, n.d.). Information on a hard drive is stored in the polarity of tiny regions. Hard disks can store huge amounts of data, up to more than 2 terabytes. However, the reliance on mechanical motion causes it to be relatively slow and prone to failure. A modern hard disk can normally access stored information at approximately 70 megabytes per second (Vertesi, n.d.). Nowadays, hard disks become widely used and it is also the cheapest form of reading or writing memory. It provides large amounts of inexpensive, permanent storage as the storage in a hard discs is cheaper and plentiful, it forms the final stage of a CPUs memory hierarchy, called virtual memory.
Flash Memory
Flash memory is a type of non-volatile memory that can be electrically erased and reprogrammed in units called blocks (Rouse, n.d.-b). Toshiba introduced it in 1984, flash memory was developed from EEPROM (electrically erasable programmable read-only memory) (Rouse, n.d.-b). There are two main types of flash memory, called NAND and NOR logic gates. The individual flash memory cells exhibit internal characteristics similar to those of the corresponding gates. Whereas EPROMs had to be completely erased before being rewritten, NAND type flash memory may be written and read in blocks or pages which are generally much smaller than the entire device. NOR type flash allows a single machine word (byte) to be written, to an erased location or read independently (Rouse, n.d.-b). The NAND type is primarily used in memory cards, USB flash drives, solid-state drives that was produced in 2009 or later, and similar products, for general storage and transfer of data(Rouse, n.d.-b) . NAND or NOR flash memory is also often used to store configuration data in numerous digital products, a task previously made possible by EEPROM or battery-powered static RAM (Rouse, n.d.-b).
Optical Disc
Optical Disc is actually an electronic data storage medium that allows it to be read and written to using a low-powered beam. There are a couple types of optical discs which are ROM, R, RW, RAM,+AND-,DL and DS (Optical Disc Types. n.d.)
These various formats of optical discs can be overwhelming at first however there is a way to easily identify them. The most basic form of data-holding CD or DVD which is the one that can only be read is formally known as CD-ROM or DVD-ROM. ROM here stands for “read only memoryâ€. It’s also considered “non-writeable†(CD-ROM, n.d.)
Next, a CD-R,DVD-R or DVD+R may only be able to record or written on, but only once. The R here stands for “recordableâ€. This “write-once†process uses a light-sensitive dye recording layer to which information is irreversibly written by means of laser heating and altering it, this creates a pattern of marks mimicking those of a pre-recorded CD OR DVD. This is why the writing process is sometimes called “burning†(Rouse, n.d.-a)
A CD-RW,DVD-RW OR DVD+RW may be recorded (written on) many times. RW here stands for “rewriteableâ€. The rewriting process employs a metallic “phase-change†recording layer that can be repeatedly altered and restored by the writing laser to about 1000 times. CD or DVD drives capable of writing (as opposed to just reading) can write to either R or RW discs. ( Beal, n.d.)
Lastly, DVD-RAM which also uses phase-change technology however it can be rewritten about 100,000 times. With its hard sectors, random access capabilities and optional cartridge , DVD-RAM actually is more like a traditional hard drive storage media as opposed to DVD-RW and DVD+RW. ( Rouse, n.d.-d)
So what’s the difference between “+” and “-” for DVDs? Unfortunately, rival industry groups DVD Forum and DVD+RW Alliance could not agree on a data format. Fortunately, most computers now incorporate “dual-standard” DVD drives, which can handle either format. You’ll see them referenced as “DVD+/-RW” drives.
As noted, DVDs can use two sides to double recording capacities. An alternative approach to doubling is provided by “dual-layer” DVDs — DVD-R DL and DVD+R DL, depending on whether the – or + format is supported. These have two data-holding layers on a single side with a semi-reflective coating between. The focus of the laser is changed to access the shallow or deep layer. Such disks can hold about 8 gigabytes on a single side (and 16 gigabytes on double-sided DLs). CDs come only in the single-layer, single-side variety ( Fast Guide to CD/DVD, n.d.)
Virtual Memory
Virtual memory is a common part of most operating systems on desktop computers (Tyson, n.d.). The enormous benefits to users at a very low cost has resulted in virtual memory becoming common. Most computers today have something like 32 or 64 megabytes of RAM available for the CPU to use. However, the amount of RAM is insufficient in running all of the programs that most users expect to run at once. Virtual memory frees up space in RAM to load new applications but if the system is too heavily relied on a significant performance drop can be seen (Tyson, n.d.).
Conclusion
The computer memory is very important since it decides whether our data or information is being saved or not. Computer memory comes in different forms, size, and capacity to provide various functions to the computer users in order to make their life easy. The manufactures also made improvements periodically to make sure that their products match the desire of consumer. Technology helps human in many ways including the invention of computer memory like USB,CD and DVD and etc. People can use these memory to store information or data as a backup to ensure that their data will not be lost, corrupted or disappeared. Technology brings lots of advantage to this world and it also improves the lifestyle of individuals