Memory in a computer is the hardware integrated circuits that store information for immediate use in a computer. However, most forms of memory are temporary, meant to be written and rewritten over, and do not save data permanently. This means that if there is an outage of power, the data is lost.
Volatile memory
Volatile memory is a type of computer memory that requires power to maintain stored information. If the power is interrupted, the data is lost. Volatile memory is used for several different purposes, including primary storage, which is faster to access than mass storage like a hard disk drive.
Random-access memory (RAM) was first invented in the 1970s to store data and machine code currently being used by a computer. RAM allows data to be read or written in almost the same time regardless of the physical location of data inside the memory. RAMs greatest advantage is that it does not suffer from mechanical limitations like media rotation speeds or arm movement the way that hard disks or CDs do.
DRAM
Dynamic Random-Access Memory (DRAM) is a type of memory used for data or program code that a processor needs to function. DRAM uses pairs of one transistor and one capacitor, storing one bit in each pair, and is found in PCs, workstations, and servers. Random access allows the PC processor to access any part of the memory directly rather than having to proceed sequentially from a starting place. DRAMs biggest drawback is that it requires a new electronic charge every few milliseconds to compensate for leaking charge from the capacitor. DRAM is simple to design, fast, and low costing compared to other types of memory. However, it is volatile and consumes a lot of power.
SRAM
Static Random-Access Memory (SRAM) uses a cell of six transistors in a cross-coupled flip-flop configuration. SRAM’s biggest advantage over DRAM is that it retains data bits for as long as power is being supplied and does not need to be periodically refreshed. It is faster but more expensive than DRAM and is used primarily for cache memory.
Non-volatile memory
A type of computer memory that can retrieve stored information even after power has been cycled. Non-volatile memory comes in electrically addressed systems (read-only memory) and mechanically addressed systems like hard disks, optical disks, and magnetic tape. Electrically addressed systems are expensive and have limited capacity, but are fast, while mechanically addressed systems are cheap, but slow.
Read-only memory (ROM)
ROM is used in computers and electronic devices. Data stored in Read-only memory (ROM) cannot be electronically modified, only read, after manufacture. ROM is useful for storing software that rarely changes during a system’s life, which is often called firmware. Firmware is usually the low-level control of a device’s hardware, like a TV remote’s controls.
Programmable read-only memory (PROM)
Invented in 1956, PROM is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. The data in these bits is permanent and cannot be altered. PROM is used in digital electronic devices, usually to store low-level programs like firmware or microcode. The major difference between ROM and PROM is that ROM’s data is written during manufacture, while PROM’s data is written after manufacture.
Erasable programmable read-only memory (EPROM)
An array of floating gate transistors individually programmed by an electronic device; EPROM’s data can be erased by exposure to a strong ultraviolet light source. EPROM is distinguished by the transparent window of fused quartz on its package, through which the silicon chip is visible, which is what allows for exposure to the ultraviolet light.
Electrically erasable programmable read-only memory (EEPROM)
Non-volatile memory is used in computers, as well as in microcontrollers for smart cards and remote keyless systems, and other devices to store small amounts of data but allowing individual bytes to be erased and reprogrammed. Organized as arrays of floating-gate transistors, EEPROM can be programmed and erased in-circuit. However, EEPROM has a limited lifespan for erasing and reprogramming, up to one million operations in modern EEPROMs.
Flash memory
Solid-state non-volatile computer storage medium that can be electrically erased and reprogrammed. The greatest advantage flash memory has over EEPROM is that while EEPROM has to be erased and rewritten, flash memory can be written and read in blocks or pages. Found primarily in memory cards, USB flash drives, and solid-state drives.
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