Iâ€™ll try to explain a bit better in laymanâ€™s terms for people who are unsure of how a write-back disk cache works and how SSD caching such as VeloSSD improves upon it.
VeloSSD works as a write-back disk cache, but instead of using RAM for the cache, it uses spare capacity on an SSD as its cache.
Hereâ€™s how a write-back disk cache works: When data is read multiple times from the hard disk, this data is stored in the cache such that when this data is accessed again, it reads many times quicker than directly from the hard disk. In the real world, this is like storing frequently accessed documents on your desk rather than in a filing cabinet.
When data is written to the hard disk, this is stored in the cache to allow the write operation to run many times quicker than writing directly to the hard disk. When the hard disk is idle, such as when the user is browsing the web or editing a document, the data stored in the cache is written to the hard disk in the background. In the read-world, this is placing documents for the filing cabinet on a corner of the desk and later placing them in the filing cabinet during a quiet period.
Windows uses unused RAM as a small disk cache, so even if you have very little running, Windows puts that spare RAM to use. For example, when an application is launched just after Windows has finished loading, it can take 5 to 10 seconds to appear. When this application is closed and reopened a few minutes later, it may appear to launch instantly. The reason it launches so quick the second time is that Windows has the applicationâ€™s data in the RAM cache. It is similar for file copy operations in that copying a folder of files for a second time appears to go a lot quicker than the first time.
However, once the PC is rebooted or another RAM/disk intensive application is used, the data in the RAM cache is lost and thus the application takes 5 to 10 seconds to launch again. By using an SSD has a huge disk cache (e.g. 64GB of SSD vs. 8GB of RAM), a much greater range of applications including the Windows start-up processes can be stored in the cache. Unlike a RAM cache, this data remains in the cache when the PC is powered off, rebooted or during heavy multi-tasking where most of the RAM is used.