PCs are complicated machines, filled with dozens of smaller components, all working together. Anyone who has worked with PC hardware is familiar with the main specifications of drives, such as capacity, read/write speeds, and platter rotation speeds of hard drives. However, there is a lesser-known and often overlooked feature that affects the speed and performance of your storage drives. The feature is known as random access memory (RAM) or cache for hard disk drives (HDD) and dynamic random access memory for solid state drives (SSD). Let’s take a quick look at what HDD and SSD What are caches and how do they work?
What is hard drive cache?
The hard drive cache is often referred to as the disk buffer. With that name, its purpose becomes a little more transparent. It acts as a temporary memory space while the hard drive reads and writes data to the permanent storage on the platters.
You can think of a hard drive’s cache memory as RAM that is explicitly designed for the hard drive. Hard drives have built-in microcontrollers that govern and process data coming in and out, much like a CPU. The hard drive RAM works together with the microcontroller to store memory while processing.
You can also think of hard drive caching as similar to buffering related to streaming content. Everyone has faced streaming a video on a slow connection. The video player waits before or during playback to collect data to continue playing the video more smoothly as it progresses. Hard drive cache allows a hard drive to do the same thing by reading and writing data.
How does hard drive cache work?
As the hard drive reads and writes data, it extracts it from the platters. Very often, the hard drive works with the same data repeatedly, since the person using the computer usually works on one or two tasks at a time. The hard drive stores the data that you or your programs use most frequently and most recently in its cache, eliminating the need to extract it from the platters every time the data is needed. This action speeds up the performance of the unit.
Hard drives: reading from front and back
Typically, a hard drive doesn’t just collect the data it needs. It also reads the data around it. Hard drives are not efficient. Spinning platters and read/write heads are inherently limited by moving physical parts, which are much slower than SSDs without moving components. Therefore, hard drives try to compensate by guessing.
When a user or program requests data (reminds me of Tron), the hard drive reads that data and the surrounding data from the platter and buffers it all. Since there is a good chance that the surrounding data is similar, the unit assumes that the user or process will also request the surrounding data soon.
Hard drives: nightly data flow
There are many different steps to recover data from a hard drive. Each of them takes time and rarely synchronizes. Transferring data from the hard drive via SATA generally occurs faster than the HDD can read and write data to the platters. Disk buffering is often used to even out this data flow and make the process much smoother.
Hard drives: minimize waiting times when writing
Once again, hard drives are slow. They are probably the most time-consuming part of any computer due to their physically moving parts. Writing data is usually “painful” for the user.
Hard drives: the purpose of cache
Hard drive cache (RAM) helps speed up the data writing process by virtually fooling the rest of the computer. A hard drive will store data in its cache and begin writing it. Instead of waiting to write all the data to the platters, the HDD tells the computer that it has done so. The PC or Mac continues to send more data or moves on to other tasks, believing the process is complete. Either way, this allows the computer to continue to the next event.
However, data caching has a disadvantage. While the hard drive tries to keep its promise of writing data, you can lose it. If the computer turns off suddenly, all cached data will disappear. RAM/cache is volatile storage.
Speed up hard drives
A larger hard drive RAM (cache) does not mean faster drive performance directly in inpidual tasks. It’s not like it’s making the puck move faster. However, having a disk buffer allows a disk drive to multitask much more efficiently and is probably something you need.
It is rare for a unit to do only one thing or only interact with one process at a time. Disk-based hard drives remain well-known storage devices in modern PCs. However, SSDs are gradually replacing HDDs. Even with a single task, multiple programs may need to access the drive’s storage simultaneously. You may be working with two or more files, experiencing background tasks, or even receiving updates.
Servers are another space where it is essential to have some RAM on the hard drives. Server hard drives will always do several things. Think of a database behind a website. Every time a user completes an action that the website must store or record, the site accesses the information and writes it to the database. Every time someone visits that website, they read from the database. It would be strange if the drives that store that database did not perform multiple tasks simultaneously.
What is cache on SSDs?
SSDs are not as slow as physical hard drives, so do they also need some cache? In short, they do. While the RAM in hard drives behaves like the RAM in the PC or graphics processing unit (GPU), the cache in solid-state drives serves as DRAM. It is much faster and keeps up with SSDs.
Although SSDs are much faster than their disk-based counterparts, caching still offers advantages. Solid state drives still use it to regulate input/output and provide faster read and write access. Meanwhile, some SSDs do not have built-in DRAM. It saves energy consumption but forces units to compensate in other ways.
Another thing to keep in mind is that SSDs write in batches rather than sectors, so they have to load groups of data, add them from the cache, and then put them back in and move on to the next group of data. This is why DRAM cache is beneficial.
In general, cache does matter, even on SSDs. It’s not as important as the specs of the head unit, but you should consider it. If your hard drive is multitasking or running continuously, such as with a server, for development, or even for gaming, look for larger RAM sizes. You will see the greatest benefits from it. Home users looking for a storage drive for occasional use don’t have to worry about it as much, although multiple tabs in a browser along with a YouTube video and two spreadsheets, all while receiving updates, can slow things down. For SSDs, the waters are a little muddier, but DRAM is still worth considering in your decision process. However, other factors can easily overshadow it.
