The CPU inside a computer works with the help of an electric current. When the electric current is high, we interpret it as “1” and when the current is low, we interpret it as “0”. For example, for a computer, the digit 10 is 1010.
So, if you want your computer to multiply 10 by 10, this binary number will become pretty huge.
Due to the limited memory resources within a CPU, which require a considerable number of 0s and 1s, the computer is generally always in need of space to store and retrieve these bits.
Although the CPU has its own memory called cache, it is pretty limited in terms of size and is also quite expensive. A much smaller memory space for the CPU is called Registers, but it is even smaller in terms of space.
We install a type of memory called Random Access Memory (RAM), also known as DRAM, in our computer. The cache memory acts as an intermediary between the CPU and RAM. Therefore, if the data is flowing out from the total register and then into cache storage, it would automatically go to RAM. RAM works in tandem with the CPU as temporary storage. However, it is a volatile memory that loses data once the power is cut off.
Then, if data needs to be stored permanently, we use computer storage, such as hard drives and SSDs.
How does Computer memory work?
Since the cache memory is always installed inside the CPU and we have no control over it, we will not discuss it here. Your computers also have ROM (Read-Only Memory), but this is a topic for another discussion. Today, we will discuss the RAM directly.
Random Access Memory (RAM) is a type of temporary (volatile) memory designed to work faster, but not for permanent storage purposes. The CPU can access it randomly, which is another reason it is so fast.
It is based on capacitor storage, which requires continuous charging or refreshing to retain the stored information. Capacitors are prone to current leakage, and the data is stored in the form of electric charge. Therefore, the status of these capacitors must be checked frequently, and appropriate high or low voltage must be applied to retain the charge and, consequently, the data.
The charged state of a capacitor is considered high (1) and discharged (0). When we combine Thousands, Millions, and even billions of these microscopic capacitors, we can create a random-access memory that is suitable for working alongside cache memory.
Imagine your CPU has a large calculation in hand, and there are thousands of steps with millions of bits and carries to re-collect and re-calculate. Perhaps the cache memory isn’t enough to store all the required data.
Now, the CPU will use the RAM to store those larger data sets and reuse them for calculations. You may have realized the second reason why this would slow down the processing. Yes, the distance between the data and the CPU has increased. However, RAM is significantly faster and more responsive than any of the fastest SSDs available.
How does computer storage work?
The process of using permanent storage devices by the CPU, i.e., hard drives or solid-state drives, is nearly identical for the host system. However, this is not the case with the devices themselves.
From the same example we took above, the calculations are now complete, and the CPU realizes that we have instructed it to create a text file with the result. It must be stored in a secure location so that it remains intact even when the system is turned off. Here comes the permanent storage of the computer in the picture.
The data will now be processed through the cache and RAM, and then written to storage.
If the primary storage drive is a hard drive, it would be sent to the HDD controller, which would write it bit by bit by switching the N and S sides on a magnetic platter. For retrieval, the controller would check these states with the help of the read/write head and return the data.
In the case of SSDs, the SSD controller takes the inputs and programs or writes the NAND Flash cells bit by bit, while also recording the location. For retrieval, it reads the data from the area and sends it back to the CPU.
Now, the distance between the origin and the target storage has increased even more. So, latency increases. Additionally, permanent storage devices are significantly slower than RAM. However, we are acquiring a larger storage space, which will hold the data in the long term, both internally and externally. So, we compromise the speed for this benefit. However, the modern SSDs are pretty fast and eliminate any chance of storage bottlenecks.
Difference between Computer Memory and Storage
There are several key differences between computer memory and storage that we should address in our article.
| Aspect | Computer Memory (RAM) | Storage (Hard Drive, SSD) |
|---|---|---|
| Definition | Temporary data storage used by the CPU | Permanent data storage for long-term use |
| Type of Data | Volatile: Data is lost when power is turned off | Non-volatile: Data is retained even when power is off |
| Access Speed | Very fast, measured in nanoseconds | Slower than RAM, measured in milliseconds |
| Cost | More expensive per GB | Less expensive per GB |
| Capacity | Typically smaller capacity (GB to a few TB) | Larger capacity (from GBs to multiple TBs) |
| Function | Holds data and instructions that CPU actively uses | Stores operating system, applications, and user data |
| Primary Components | Made up of integrated circuits (ICs) | Consists of spinning disks or solid-state memory chips |
| Usage | Used for running programs, processes, and tasks | Used for storing files, documents, and applications |
| Physical Location | Located on the motherboard | Usually housed externally or internally in a computer |
| Persistence of Data | Data is lost when power is turned off | Data is retained even when power is turned off |
| Performance Impact | Can significantly impact system performance | Typically has less impact on system performance |
Purpose of Computer Memory
As the scale of computers increases, the data they have to work with is becoming larger and larger. To have 2 to 3 tabs of Google Chrome (Text) open at a time, you need around 300 MB of RAM. The more processing your system has to do, the more RAM it requires.
We can’t have that much cache inside our CPU, as it would make it too expensive and bulky. Therefore, we add temporary memory that holds the information the CPU is currently working on.
Therefore, we can consider the computer memory a slower extension of the cache. It is a larger pool, albeit with a compromise in speed.
It is designed not to retain data permanently, but to provide the CPU with the necessary resources to fulfill the demands of all the software that must run for our computers to function correctly.
Purpose of Computer Storage
Once the problem of storing large chunks of temporary data is solved, we need a secure location to store permanent data that remains intact when the system shuts down. Otherwise, we won’t be able to store our photos or videos on our computers.
For that, we use computer storage. Again, the data is stored in the form of bits, but the space has been increased. Now, we are talking in thousands of gigabytes. In 2024, the prominent permanent computer storage devices are Hard Drives and solid-state drives.
The primary purpose is to hold the OS and software data. These storage devices can release that data whenever required and load it onto the RAM. These drives also facilitate organization, backup, recovery, and data sharing.
They are also helpful for capacity expansion and storing big multimedia files.
Speed of Computer Memory
Generally, writing to and reading from computer memory (RAM) comprises four steps, i.e.
- Memory Addressing
- Address Decoding
- Row Activation
- Column Access
- Data Transfer
- Write Confirmation (In case of Writing)
Now, if we examine the DDR4 RAM, it takes approximately 10 to 15 clock cycles to complete either of these operations.
To compare, the L1 cache generally requires 1 to 2 clock cycles for the same. The L2 cache typically takes 5 to 15 clock cycles.
As the DDR (Double Data Rate) increases, so does the speed. However, due to fundamental design barriers, the RAM can never reach the speed of the cache.
Memory speed is typically denoted in megahertz (MHz) or gigahertz (GHz). For example, a memory module with a speed of 3200 MHz means that it can operate at a frequency of 3200 million clock cycles per second.
Speed of Computer Storage
The process of writing data on a computer storage device varies depending on the type of device. As we discussed above, HDD stores data mechanically on the magnetic platters. On the other hand, SSDs are based on transistor-based memory, which is exceptionally faster than HDDs.
Due to the mechanical components included and the inherently slower writing process, the maximum read/write speed of any hard drive is approximately 250 MB/s. This speed is directly proportional to the RPM at which the magnetic platter can rotate. However, hard drives are available at a lower price per GB.
The SSD technology, on the other hand, is rapidly improving. The Gen 5.0 drives are here, and SSDs like the Samsung 9100 Pro and WD Black SN8100 are achieving speeds beyond 10GB/s in sequential data read and write. Although the random and sequential read/write numbers will always be significantly apart, that is a discussion for another time.
Speed Comparison Between Computer Memory and Storage
Let’s take an example of a 3200MHz DDR4 RAM. The data rate will be:
3200MHz * 2 = 6200MT/s
Now, the RAM has a 64-bit bus width, which means it can handle 8 bytes in total.
The data transfer rate of this RAM will be 6400MT/s * 8 bytes = 51200 MB/s.
These are approximate numbers, but comparing this speed to the highest possible levels of SSDs, i.e., ~14,000 MB/s to date, reveals that it is pretty high.
RAM Bandwidth Calculator
Types of Computer Memory
1. Random Access Memory (RAM):
RAM is divided into several categories based on its usage and characteristics, including:
DRAM (Dynamic RAM): A Common type of RAM used in most computers. Requires periodic refreshing to maintain data.
SRAM (Static RAM): Faster and more expensive than DRAM, used in cache memory and registers within the CPU.
DDR SDRAM (Double Data Rate Synchronous Dynamic RAM): An advanced type of DRAM that offers higher data transfer rates.
SDRAM (Synchronous Dynamic RAM): Synchronized with the CPU’s system clock, allowing for faster data access.
2. Read-Only Memory (ROM):
ROM is non-volatile memory used to store firmware and permanent system instructions that the user can’t change.
Data such as boot-up instructions, basic system functions, BIOS, and other essential information is stored in this memory.
ROM is typically used to store critical system settings and firmware that control hardware components.
3. Cache Memory:
As we discussed earlier, cache memory is a small, high-speed memory located directly on or near the CPU.
It stores frequently accessed data and instructions to speed up CPU operations by reducing memory access latency.
Cache memory is divided into several levels (L1, L2, L3) based on proximity to the CPU and size.
4. Virtual Memory:
Virtual memory is a memory management technique used by operating systems to extend the available memory beyond physical RAM.
It utilizes a portion of the computer’s storage devices (e.g., hard drive, SSD) as temporary memory space to store data and swap it in and out of RAM as needed.
5. Registers:
Registers are the smallest and fastest type of memory used by the CPU to store data temporarily during processing.
They are built into the CPU and are used to hold data, instructions, and memory addresses during program execution.
Types of Computer Storage
Primary Storage:
Don’t get confused when I say RAM is the primary storage of your computer. This is just because it is the first storage that interacts with the CPU. It is temporary, but nonetheless.
Secondary Storage:
Hard Disk Drives (HDDs): Hard Drives are the mechanical drives that use magnetic material to store data in the form of changing magnetic orientations.
Solid-State Drives (SSDs): SSDs are modern storage devices that use either the SATA or PCIe interface for data transmission. Modern NVMe SSDs offer higher bandwidth, lower latency, and a highly scalable nature. With the help of NAND flash, they achieve very high data transfer rates.
Hybrid Drives (SSHDs): Combination storage devices that integrate both HDD and SSD technologies. SSHDs utilize an SSD cache to store frequently accessed data, thereby improving performance without compromising storage capacity.
External Storage Drives: Portable storage devices that connect to computers via USB, Thunderbolt, or other interfaces. These include external HDDs, SSDs, pen drives, and hybrid drives used for backup, file storage, and data transfer.
Network Attached Storage (NAS): These are specialized storage systems connected to a network, allowing multiple users to access and share files and data. NAS devices often contain multiple hard drives configured in RAID for data redundancy and enhanced performance.
Conclusion
This was a fundamental difference between computer memory and storage. Internally, computers are highly complex and require a solid understanding of both electronics and software. Nobody knows completely how a computer works. However, with the help of abstraction and articles like this, we gain a fair understanding of how these things work. If you enjoy this article, please leave a comment.
