What is computer memory what is computer secondary memory and memory versus(vs) storage|

What is computer memory

What is computer memory  what is computer secondary memory and memory versus(vs) storage| what is the difference memory and storage on a computer What is difference between main memory and cache memory?What is computer memory How many types of memory?what is computer memory?What is computer memory  what is computer secondary memory and memory versus(vs) storage| different between primary memory and secondary memory? examples of primary memory and secondary memory difference between primary memory secondary memory storage

What is a secondary memory?

Computer memory is very much like the short-term memory of your brain. it is where things are stored temporarily while the computer works on them. by far the most common version of memory is a (set of ) computer chips called random access memory, or  RAM  for short. A typical computer will have at least 64 MB  of  RAM  storage, in other words: 64*220*8 bits that can be on or off. the CPU  can store data in RAM  by changing the value of certain bits, and read the data back by examining the value of these bits.

(computer memory and works)

When a computer is at work, any data that it wants to work on is first copied into memory. this includes any programs that you are running, and any data that these programs are using. most software comes with a recommended minimum amount of RAM  that it needs for proper operation. if your computer has less than the recommended amount of RAM  the software may not fit into memory, and as a result will not run properly-or even at all. as a rule of thum you should  the RAM  requirements of the software you are planning to use, and buy double that amount to allow for some headroom. better still is to buy as much  RAM  as you can afford. as it is the easiest way to make sure your computer performs adequately with most applications.

(how computer memory works)

RAM is "volatile", meaning that information in it is maintained only as long as the chips are fed electrical power. its contents are erased when the power is switched off. therefore, when you turn off your computer all information in the RAM  is lost. any information that you want to keep should be store somewhere permanent, on something we call secondary memory/storage. (When contrasted with secondary storage, computer memory is often referred to as primary storage.) this is why you have to save your work to a hard drive or floppy disk before you switch off the computer.

computer memory can also come the form of ROM  (for read only memory). the difference between RAM  and ROM is that the contents of ROM  are fixed and cannot be changed by the CPU-or anybody else, for that matter. ROM is often used to store software that is final and need not be changed anymore, An example would be the software that  operates your mobile phone. the phone manufacturer buys components called PROM  (for "programmable" read-only memory) and store software on it to make the phone works as it is intended.

(primary memory)

When technology advance, it may be necessary to upgrade the software in ROM  form time to time. rather that replacing the ROM , people may use components called EPROM (for "erasable" programmable read-only memory) whose contents can be changed using some external agent, such as ultra-violet light.

modern computers make extensive use of memory to store all kinds of data. consequently the speed at which the RAM  operates is crucially important for the overall speed of the computer. a fast  CPU  will have to continually wait if it is equipped with slow memory-a chain is only as strong as it weakest link!

Secondary storage

Secondary storage is like your brain 's long-term memory. here is where all your data and programs are stored permanently. everything from the operating system to your word processor, the letters you wrote, your emails, your drawings, all this has to be stored on a secondary-storage medium such as a floppy disk, hard disk, or  CD-ROM  if you want the computer to remember it by the time you turn it back on.

(this is the secondary storage )

Now-a-days two type of secondary storage are popular: hard disc and CD-ROM s A CD-ROM is a plastic disc with microscopic pits pressed into it. to read the CD-ROM a laser beam is cast onto its surface. if there is no pit at that position of the disc, the laser beam is reflected by a metallic coating on the disc and captured  by a lens:a pit causes the laser beam to not be reflected. in other words, we have created an on/off situation (corresponding to the presence or absence of a pit at any given position on the disc), which can be utilized to store the value of  a single bit. this allows us to store data on a CD-ROM. A  standard CD-ROM  has a capacity of 650 MB.

A (recordable) CD-RW works in a similar fashion.  However it does not contain actual pits, but a reflective coating that can be melted by means of a powerful (writing) laser beam. melting the coating causes the disc to become no-reflective at that position. the process of reading a CD-RW  is identical to that used for a CD-ROM . A HARD DISC IS SIMILAR TO a CD-ROM, but it contains disks that are made of metal rather than plastic. bits are stored on a hard disc by means of tiny magnets. the capacity of a typical hard disc is 20 GB, because the magnetism applied to a hard disc can be erased if required, a hard disc can both read and write information. in addition hard disks are much faster than CD-ROMs , but unfortunately-you probably were expecting a catch by now they are also much more expensive.

(this is a CD-ROM Image)

A ROM is also long-term storage with fast access.a common device that could serve as fast and permanent storage is the EEPROM (for"electrically" erasable programmable read-only memory). instead of using ultra-voilet light to erase the contents like the EPROM, an electrical signal will do. EEPROM  is often called "flash" memory since they could be chabged   "in a flash" . such components are used in SIM  cards of mobiles phone, the octopus card, memory to store photos in digital cameras, etc at this time it is very expensive to make EEPROM  with large capacity (such as 512 MB and up) but, as it is with most hardwae devices, prices will drop and performance will improve in the future.

Memory  versus(vs) Storage

Both memory and secondary storage have relative advantages and disadvantages . the main advantages of RAM is that it is much faster than any kind of secondary memory/storage. and faster memory allows for faster computers. RAM  is so fast because it is an electronic memory, whereas hard disks and CD-ROMs store and access data by mechanical means. RAM  is approximately 1000 times as  fast a decent hard disk! the speed at which  secondary memory performs may not be as crucial to the overall speed of the computer, but a fast hard disc can make a computer 'feel' significantly faster.

also cost is an important factor.  RAM  and ROM  are much more expensive than secondary storage:a 20 GB  hard disc cells for less than HK$400, but for 20 GB RAM  you would have to pay in excess of HK$20,000! and CD-ROMs  are even cheaper than hard disc: to store 20 GB  on CD-ROMs  you would need to spend little more than  HK$40. LAST  but not least, as we have seen  RAM  is volatile whereas secondary storage is permanent.

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