The primary difference between RAM and ROM is that RAM is a volatile form of memory and is used to store information that can be safely discarded when the computer turns off or loses power. On the other hand, ROM is a form of non-volatile memory primarily used to store very vital pieces of information permanently. Said information might include firmware, system software, etc. A particular type of ROM – Flash Memory is used in Mass Storage devices, such as thumb drives and SSDs, to store any sort of information, vital or otherwise, in a high volume yet compact package.
But what is volatile and non-volatile memory? Volatile memory is a type of memory that will lose the stored data if its power supply is terminated. On the other hand, non-volatile memory does not lose the data stored even if power is disconnected. In other words, volatile memory is temporary, while non-volatile memory is permanent. However, before we jump into what are the other differences between RAM and ROM, we take a glance at what is RAM and ROM.
RAM
RAM stands for Random Access Memory. The reference to the memory device in your computer, commonly known as the system memory, can be used interchangeably with RAM. It can be thought of as a two-way street with houses having a unique address. Each house stores a byte of information where each byte is composed of 8 bits. A bit can have one of two states – 0 or 1.
Electronically speaking, a capacitor and a transistor can make up a DRAM bit, where the transistor acts as a control mechanism. In contrast, the presence or absence of charge in the capacitor defines the state of the bit. Another type of RAM called the SRAM is way faster than DRAM and resides inside the microprocessor package. To thoroughly understand the differences mentioned later, or if you are looking for more information about DRAM and SRAM, we strongly recommend visiting our article discussing RAM in far more details.
ROM
ROM stands for Read-Only Memory, which, as mentioned previously, is a form of permanent memory, where traditionally data could only be read, not altered. However, modern ROM technology is far more forgiving, but we would assume that ROM cannot be altered for the sake of this article. ROMs come in varying flavours, but their most common utility is storing crucial pieces of information, which generally do not require frequent erasing or rewriting. Such information might include firmware, BIOS, etc.
ROM technology is also found in external storage solutions such as the CD-ROM or DVD-ROM. However, most common types of ROM cells have a limited write endurance, which means there is only a limited number of times the cell can be rewritten before it becomes permanently unusable. To find out more about ROM or why memory cells degrade, we strongly suggest checking out our article discussing ROM.
Perhaps the most common use of ROM technology is in SSDs, which operate using a memory technology called Flash memory. The primary factor separating flash from standard ROM technology is that flash has a remarkably high I/O performance, but just like any other EEPROM, it has a finite write endurance. Nevertheless, modern flash has matured enough to the point that it is not uncommon to find SSDs with endurance ratings in the hundreds, often thousands of terabytes.
Difference between RAM and ROM
The following table summarizes the most significant differences between RAM and ROM:
| Aspect | RAM | ROM |
| Persistence of stored data | Volatile | Non-volatile |
| Rewriteable | Data can be rewritten in the same memory cell any number of times | Data stored in ROM can be read but not altered |
| R/W performance | RAM is massively faster than ROM | ROM is slower than RAM |
| Role | Data/programs are always loaded into the RAM from the ROM before being executed | ROM permanently stores programs or data. Data is always loaded into the RAM before fulfilling its desired purpose |
| CPU accessibility | CPU can directly access the RAM | CPU cannot access the ROM |
| Memory size and capacity | Large size with more capacity | Relatively less size with lower capacity |
| Common underlying electronics | Flip-flops, transistors and capacitors | Floating gate MOSFETs |
| Endurance | RAM cells have practically infinite endurance | ROM cells generally have limited endurance |
| Used in | Cache memory, primary memory, buffers | Micro-controllers, Firmware, BIOS, etc. |
| Common utility | Temporarily stores instructions or data to be processed by the CPU, or caches frequently accessed data. | Stores instructions for bootstrapping, Hardware IDs, Programs in microcontrollers, etc. |
