Computer Memory Types Explained: Flash, SSD, RAM, EEPROM, HDD

If you’re buying or building a computer today, it will come with a hard drive (HDD), and it may include an upgraded solid-state drive (SSD) for program and media storage. You’ll also have a certain amount of some kind of RAM for short-term storage. You may hear confusing terms such as flash, EEPROM, and EPROM thrown around while you’re shopping. While you might have some vague idea of what each of these does - and know that some of these terms can mean the same thing depending on context - an overview of these features may help you choose the right computer. We’ll provide some clarity on where to use each type and their advantages. So let’s start with a common question; What is RAM?

Random Access Memory (RAM) - What is RAM?

Unlike the other types of media, manufacturers use Random Access Memory (RAM) to store programs and additional information temporarily. With RAM, that temporary storage means all stored data disappears when the device loses power. Your operating system and any currently-running programs utilize this type of storage, allowing this extremely fast - and relatively expensive per gigabyte - medium to speed up your computer use.

If your computer doesn’t have enough RAM to run a program, your system may substitute memory from your HDD or SSD as virtual memory. Using substitute memory will allow these programs to run, but you’ll see much slower performance.

Hard Drive (HDD)

Hard drives first entered the world stage in 1956, with the introduction of the RAMAC 305 system. With a capacity of 5MB (5 million bytes) of data, and cost roughly $50,000, this early drive evolved into the many TB (trillion byte) drives we see available today for under $100. A quick search reveals that you can purchase an 8TB drive for just over $200.

How HDD Works

Hard drives physically spin a platter into the correct position for the read head to move in and out on the platter’s diameter. Spinning the platter allows the read head to read the magnetic state of different positions and change them as needed. HDDs can read and write data in the range of 100s of megabytes (MB) per second when ordered sequentially, but you’ll see much slower access if data is physically scattered around the drive. This kind of access speed partially depends on how fast the platter can spin. You can find these drives with ratings of 5400, 7200RPM, and faster.

We’ve experienced a nearly unfathomable - by a factor of hundreds of millions - increase in the amount of storage space per dollar available in the last 60 years. These speeds also seem incredible if you consider what’s happening inside one of these devices. We’re now starting to see this medium give way to SSDs, which have important speed and reliability advantages.


EEPROM stands for Electrically Erasable Programmable Read-Only Memory.You might be wondering; How does EEPROM work?

- Instead of reading and writing information magnetically, EEPROM stores bits using semiconductor technology.

- EEPROM requires no moving parts, and like HDD storage, it can maintain its state through power cycles.

- EEPROM can endure many write cycles before failure some in the 10,000 range, and others up to 1,000,000 or more.

- EEPROM even serves as the basis for the flash memory used in SSD drives now available in data capacities of a terabyte or more.


You can find EEPROM in devices ranging from remote keyless access systems to microcontroller boards. While the “electrically erasable” part of EEPROMs name might seem like a throwaway phrase, don’t confuse this type of memory with“EPROM,” which stands for Erasable Programmable Read-Only Memory. EPROM chips, while non-volatile and reprogrammable, require UV light to erase a chip’s bits. They also require a higher voltage than we normally see while programming digital circuits. As a result, EPROM isn’t suitable for storing information that will change frequently.

Flash Memory vs SSDs

Flash memory is a type of EEPROM designed for high speed and memory density. As such, flash drives based on this technology can store many gigabytes of data on a USB stick smaller than your thumb, which is how they earned the name thumb drives.Taking this compact design even further, micro SD cards are roughly the size of a thumbnail and can commonly store tens or even hundreds of gigabytes of information. On a larger scale, you could cram even more data onto this type of memory, perhaps enough to act as a computer’s primary storage method. cards are roughly the size of a thumbnail and can commonly store tens or even hundreds of gigabytes of information. On a larger scale, you could cram even more data onto this type of memory, perhaps enough to act as a computer’s primary storage method.

SSD has slowly been catching up to HDD usage, especially in portable computing applications, and here’s why:

1. SSD drives don’t have to spin into position, which means they can randomly access data in a fraction of a millisecond.

2. They have I/O performance levels several times better than their HDD cousins.

3. Lower energy consumption and better reliability because of their lack of moving parts are also significant benefits of these drives.

Pros and Cons of SSD and HDD

The downside to SSD technology is that it costs more per gigabyte. However, in high-performance applications where speed is more important than the volume of data stored, this type of drive can be well worth the cost.

As this technology advances, we can expect SSD market share and capacities to continue to increase. Improvements in the speed and capacity of available RAM will continue as well. With evolution like these, computers may soon be able to handle applications we can only imagine today.

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