Explain HDD Cache and Disk Usage

[Roshen]

I have a 500GB Seagate HDD with a cache/buffer of 64MBs.
But when I use some softwares (7zip), Task Manager (Win 8.1- disk usage is 99%), it shows more than 64MBs (sometimes more than 100MBs).
.

• 
  Please explain me what this cache/buffer is.
  And why is it way more than the limit?

Thank you!

 

[aznricepuff]

The disk cache/buffer is dedicated flash memory located in the hard drive that buffers data that is being read from/written to the disk: https://en.wikipedia.org/wiki/Disk_buffer

What you are seeing in task manager is not related to your hdd's disk cache. You are probably reading how fast the hdd is reading/writing data in MB per second - this is data transfer speed. Manufacturers will usually list a disk's maximum read/write speeds as "read/write performance" or "read/write speed".

Meanwhile the disk cache is essentially a pool of RAM, so a "64 MB disk cache" means the cache size is 64 MB. There is no simple relationship between cache size and read/write performance, other that in general disks with larger caches tend to have better performance, all other things being equal.