Hard disk is the main storage where your operating system and all other things (in short, everything) are stored, the processor cannot directly access the data on it.

RAM, the random access memory is the secondary memory where data from the hard disk are loaded. Data is kept transferred to and fro between hard disk and RAM during operation. The processor can access data only from here.

ROM, the read only memory stores data permanently, it can be read or copied, but cannot be written unto it.

Jedan od razloga zbog kojih je ROM još uvijek u upotrebi je brzina - magnetni diskovi su mnogo sporiji. Drugi je činjenica da se upravljački program potreban za rad diska ne može nalaziti na samom disku. Zato je BIOS još uvijek na ROM-u. Uz ovo, mrežne i grafičke karte neke svoje osnovne funkcije implementiraju preko softvera pohranjenog na ROM-u. Dalje, u posebno teškim radnim uvjetima (vibracije, veliko ubrzanje), gdje su diskovi neprimjenljivi zbog svoje osjetljivosti, ROM je nezamjenljiv.

-A ROM chip is used primarily in the start up process of a computer, whereas a RAM chip is used in the normal operations of a computer after starting up and loading the operating system.

-Writing data to a ROM chip is a slow process, whereas writing data to a RAM chip is a faster process.

-A RAM chip can store multiple gigabytes (GB) of data, up to 16 GB or more per chip. A ROM chip typically stores only several megabytes (MB) of data, up to 4 MB or more per chip.

One of the greatest sources of confusion for computer users is the difference between a computer’s memory and its storage space. The confusion is not entirely the users’ fault. Overlapping terminology contributes, as does poor word choice. I’ll try to reduce confusion by differentiating the terms as well as talking about their overlap.

Computers have two kinds of storage — temporary and permanent. A computer’s memory is used for temporary storage, while a computer’s hard drive is used for permanent storage. Whoever selected the term memory for temporary computer storage did the world a disservice since people tend to permanently store information in our memories. If I asked you to recall your first grade teacher’s name you could, most likely, tell me because that piece of information is stored in your memory, right? This is not how computers use their memory. A computer’s memory is also called RAM which is an acronym for Random Access Memory. A computer’s memory is where information is temporarily stored while it is being accessed or worked on. For example, if I’m updating my resume, then I double-click its icon to open it. This process of opening the file, copies it from its permanent home on the computer’s hard drive (aka hard disk drive or hard disk) into the computer’s memory. Once in memory, I can edit it. If the computer loses electrical power while I am updating my resume, the most recent changes I’d made are lost. This is because the information in a computer’s memory is only kept there while electrical power is supplied. To avoid losing my most recent changes, I need to save the file. The act of saving a file copies it back to the computer’s hard drive. The contents of a hard drive remain intact even if the computer is turned off or it loses electrical power some other way.

A simple analogy I use to help remember these terms is that memory is like your desk’s work space and your hard drive is like a filling cabinet. Your filing cabinet is typically large enough to store hundreds of file folders and thousands of pieces of paper. Your desktop work space is not large enough for all of these file folders and papers.

Both temporary computer storage (memory or RAM) and permanent computer storage (hard drives) are measured in bytes. These days they are measured specifically in gigabytes (GB). If you’d like to learn more about bytes and gigabytes, please read this previous Tech Tip. This overlap in measurement systems contributes to some of the confusion.

In early 2012, a new Mac might be equipped with 4 GB of memory and a hard drive whose storage capacity is 500 GB. The primary reason for this great disparity is cost. Memory, RAM, is much more expensive then hard drive storage space. Here’s a rough comparison. One GB of RAM costs about $8, while 1 GB of hard drive storage space costs about 10 cents.

Šta bi bila cache memorija, znam da se i ona uzima kao relevantna.