Hard disk RAM or ROM

Answer 1

ROM is memory that is inherently read-only; it can not be updated except in special circumstances. For example, a BIOS chip is either read-only (burned in at the factory with preset instructions), or is "locked" for writing except under special circumstances ("Flash BIOS"); either way, from an Operating System's perspective, this data can never be updated, and is thus "read only memory". Older ROMs could only be read from front to back (they had to be read into memory before execution), while newer ROMs (such as later video game cartridges) could be read from randomly, but never updated. Games that allowed saving to a cartridge did so in a special "Battery RAM" (battery powered random access memory) or "Flash ROM" area.

The next higher level of memory is called "WORM" (Write Once Read Many), and consists of devices that can, during normal operation, accept one update to its media, and once written, can never be updated again. There are a few special exceptions to this type of memory, one of which is "EEPROM" (Electronically Erasable Programmable Read Only Memory), which can be written to only once without erasing all of its contents, but can be completely erased and written to again. Note that this is practically the same as WORM, except that the slate can be cleared.

It is most important to note that you can not write data to any WORM technology; you must start at the first byte and proceed linearly to the last byte; and this can only be done after a "flash" occurs (older EEPROMs took this literally, as it required a flash of ultraviolet light to erase them). If the process is interrupted, you must erase the entire device and start over again. Tape drives operate much the same way, in that they must be read from start to finish, and any changes means the entire tape must be re-written. While these devices are certainly not true "ROMs", since they can be erased and re-written, they can not be randomly updated, and are therefore not "RAM" devices. DVD-R and CD-R are also examples of WORM technology.

This leads us to the next level of memory, called "RAM" (Random Access Memory). RAM has the unique property of being able to be read in any order, and can be updated in any order. While some ROMs can be read in any order, they certainly can not be written in any order, which is a classification of RAM (as the term implies, to "randomly access memory", where "random" is defined as "no particular order"). In the IT world, RAM usually means "system memory", which is where programs and data are stored for execution.

However, looking at the characteristics of hard drives, it becomes clear that, since they can be updated without regards to sequential order, without wiping the entire media, and can be read in any order that the user instructs it to without scanning the entire media, they could be considered "RAM" devices (albeit, very slow devices compared to the electronic chips that we actually call "RAM"). Hard drives are not usually called RAM devices, due to the confusion that would cause with actual system memory (DDRAM, SDRAM, SIMM, DIMM, cache, etc), but they are definitely not ROM devices, since that would render them about as useful as a high-density DVD-R disc; if you messed up a DVD-R, you had to throw it away, while you can easily remove or update any data on a hard drive.

Furthermore, one of the first hard disk drives to use magnetic tracks to store data was the "IBM RAMAC", which stood for "Random Access Memory and Control"; since then, all future designs of hard drives have worked off the same principle of being able to randomly read and write data to magnetic surfaces.