Basics of Computer Memory

When someone refers to a computer’s memory, they could be referring to one of numerous different layers. If a computer just had a hard drive, it would run very slowly. That is why a computer is integrated with many different types of memory. In a general sense though, it refers to the hardware in a computer to store information.

You may have heard of someone refer to computer memory as RAM (random access memory). Main memory is referred to as RAM because instead of sequential access of memory, you access randomly at any location in memory. This can be misleading which often leads to confusion. For example, ROM (read-only memory) is also randomly accessible but is differentiated from RAM. RAM today refers to the main place the processer uses to run programs.

As technology has increased, RAM has been broken down into two sub categories: DRAM (dynamic random access memory) and SRAM (static random access memory). DRAM chips store memory dynamically which means that information can be written repeatedly at any time and data must be refreshed every few milliseconds. On the other hand, SRAM does not require refreshing which makes it faster overall. To further understand how memory operates, lets look at ROM, DRAM, and SRAM more to see why these types of physical memory are used today.



ROM

Read-only memory can either permanently or almost permanently store data. The reason it is called read-only is because it is difficult or impossible to write to. You may have also heard it referred as nonvolatile memory. This is because any data stored there will stay there, regardless if the power is off. These features allow for the perfect place to store a PC’s startup instructions. A lot of systems today use a type of ROM called electrically erasable programmable ROM (a type of flash memory).

DRAM

Dynamic RAM is the most common type of chip found in main memory. DRAM allows you to store lots of bits into a small chip. This makes having a large amount of memory affordable. Ironically, the main problem with DRAM is that it is dynamic. What this means is the contents on the chip are constantly changing with keystrokes and mouse swipes. If a system crash were to occur, the entire contents stored on a DRAM chip would be wiped. The other important aspect is that DRAM chips must constantly refresh data. Every time a refresh occurs, the processor must stop with its current tasks and refresh the data. This leads to a slower system. If you were to increase the time between refresh cycles, you would speed up your system but could cause soft memory errors. A soft error refers to a data error not cause by a damaged chip.

SRAM: Cache Memory

Static RAM is another type of memory. Unlike DRAM, it does not need constant refreshes on the data it stores. However, this causes storing memory in SRAM to be more expensive and less affordable for large amounts of it.