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A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks (platters) coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order and not only sequentially. HDDs are a type of non-volatile storage, retaining stored data even when powered off.
A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is also sometimes called a solid-state device or a solid-state disk, although SSDs lack the physical spinning disks and movable read-write heads used hard drives ("HDD") or floppy disks.
In computing, a computer bus operating with double data rate (DDR) transfers data on both the rising and falling edges of the clock signal. This is also known as double pumped, dual-pumped, and double transition. The term toggle mode is used in the context of NAND flash memory.
Names | Memory clock | I/O bus clock |
Transfer rate |
Theoretical bandwidth |
---|---|---|---|---|
DDR-200, PC-1600 | 100 MHz | 100 MHz | 0.2 GT/s | 1.6 GB/s |
DDR-400, PC-3200 | 200 MHz | 200 MHz | 0.4 GT/s | 3.2 GB/s |
DDR2-800, PC2-6400 | 200 MHz | 400 MHz | 0.8 GT/s | 6.4 GB/s |
DDR3-1600, PC3-12800 | 200 MHz | 800 MHz | 1.6 GT/s | 12.8 GB/s |
DDR4-2400, PC4-19200 | 300 MHz | 1200 MHz | 2.4 GT/s | 19.2 GB/s |
DDR4-3200, PC4-25600 | 400 MHz | 1600 MHz | 3.2 GT/s | 25.6 GB/s |