Every type of storage media has some kind of limit to how many times it can be written. This is not a problem that’s specific to SSDs, but is rather inherent in the way any sort of digital storage works. There are several mechanisms at play, both natural phenomena which cannot be circumvented and engineering trade-offs between cost, performance, power consumption and lifetime.
Unfortunately, there isn’t an ultimate answer for this question as it varies heavily depending on the implementation of the memory controller which controls communication with the NAND chips where data will ultimately end up being stored. However, I will try my best to provide a high-level overview!
No matter what type you use – hard disks, solid-state disks or even RAM – all storage devices are divided into blocks of a fixed size, which are essentially containers for the storage cells where your data are supposed to be. If you write data, these cells will get filled up with electrons – bits are 1s when they’re full and 0s if they’re empty.
Writing is done block-by-block, but reading can be done on smaller chunks called pages – typically 4KB or 8KB in modern drives (and only 2KB on some older ones). The reason why I mention this is that SSD writes happen on a granularity level of pages rather than blocks as hard disks do.
When a drive is new out of the box its NAND chips don’t have any physical limitations because no one has written to them before. However as soon as the first writes occur, the space on your drives gets marked with “defects” where data cannot be written anymore because it has been partially damaged – a process known as wear leveling.
Repairing these bad parts would be quite costly in terms of time and energy which is why manufacturers usually prefer to leave them alone and prevent further damage by limiting how many pages can be written to a single block.
It might sound simple but there are actually multiple ways in which this cap becomes active: from age or amount of write cycles performed on a chip to built-in hardware protection mechanisms. There’s no universal number that applies across all devices since different companies have different preferences when it comes to deciding what values they feel most comfortable with.
An easy way to see how this works in practice is to examine the ATA Secure Erase command which allows you to reset your SSDs so they’re in perfect working order again. This process is usually accompanied by a notification that says something along the lines of “this will only take 20 minutes, but ALL data on the drive will be lost!”.
It’s not really true that all your data are gone – it’s simply written over with 0s instead of 1s, but unless you’ve been extremely sloppy with RAID configurations or backups, everything is still there under the surface! However if you wanted to recover some files from before they were erased, it would require using special software or hardware equipment designed specifically for low-level disk recovery.
Why do ssd have limited writes?
The answer is that SSD has limited writes because of the way they are built. The underlying memory used for actual data storage is called NAND flash, which was first developed by Toshiba back in 1984.
SSD has limited writing because every type of storage media has some kind of limit to how many times it can be written. Any sort of digital storage works this way, but there are several mechanisms at play both natural phenomena and engineering trade-offs between cost, performance, power consumption, and lifetime.
Technicians or other people who want to erase their hard drives should use the Secure Erase feature which will write overall data with zeros across the entire drive! This does not mean though that all data are gone – simply written with 0s instead of 1s, but it is still more than enough to prevent data recovery.
The whole concept of hard disk storage devices was thought up following the idea that we could store information on a fixed medium and read and write information from and on this medium with the help of some mechanical and electrical components. That’s the reason why we can’t rewrite and/or delete and/or change (overwrite) existing data on a hard disk drive in one go, but rather in parts.