A solid-state drive (SSD) (also known as a solid-state disk  orelectronic disk, though it contains no actual “disk” of any kind, nor motors to “drive” the disks) is a data storage device using integrated circuitassemblies as memory to store data persistently. SSD technology uses electronic interfaces compatible with traditional block input/output (I/O) hard disk drives, thus permitting simple replacement in common applications.Also, new I/O interfaces like SATA Express are created to keep up with speed advancements in SSD technology.
SSDs have no moving mechanical components. This distinguishes them from traditional electromechanical magnetic disks such as hard disk drives(HDDs) or floppy disks, which contain spinning disks and movable read/write heads. Compared with electromechanical disks, SSDs are typically more resistant to physical shock, run silently, have lower access time, and lesslatency. However, while the price of SSDs has continued to decline in 2012, SSDs are still about 7 to 8 times more expensive per unit of storage than HDDs.
For applications requiring fast access, but not necessarily data persistence after power loss, SSDs may be constructed from random-access memory (RAM). Such devices may employ separate power sources, such as batteries, to maintain data after power loss.
Hybrid drives or solid state hybrid drives (SSHD) combine the features of SSDs and HDDs in the same unit, containing a large hard disk drive and an SSD cache to improve performance of frequently accessed data
Flash memory developed from EEPROM (electrically erasable programmable read-only memory). There are two main types of flash memory, which are named after the NAND and NOR logic gates. The internal characteristics of the individual flash memory cells exhibit characteristics similar to those of the corresponding gates.
Whereas EEPROMs had to be completely erased before being rewritten, NAND type flash memory may be written and read in blocks (or pages) which are generally much smaller than the entire device. The NOR type allows a single machine word (byte) to be written or read independently.
The NAND type is primarily used in main memory, memory cards, USB flash drives, solid-state drives, and similar products, for general storage and transfer of data. The NOR type, which allows true random access and therefore direct code execution, is used as a replacement for the olderEPROM and as an alternative to certain kinds of ROM applications, whereas NOR flash memory may emulate ROM primarily at the machine code level; many digital designs need ROM (or PLA) structures for other uses, often at significantly higher speeds than (economical) flash memory may achieve. NAND or NOR flash memory is also often used to store configuration data in numerous digital products, a task previously made possible by EEPROMs or battery-powered static RAM.
Dynamic random-access memory (DRAM) is a type of random-access memory that stores each bit of data in a separate capacitor within anintegrated circuit. The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. Since capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory.
The advantage of DRAM is its structural simplicity: only one transistor and a capacitor are required per bit, compared to four or six transistors in SRAM. This allows DRAM to reach very high densities. Unlike flash memory, DRAM is volatile memory (vs. non-volatile memory), since it loses its data quickly when power is removed. The transistors and capacitors used are extremely small; billions can fit on a single memory chip
Static random-access memory (SRAM) is a type of semiconductormemory that uses bistable latching circuitry to store each bit. The termstatic differentiates it from dynamic RAM (DRAM) which must be periodicallyrefreshed. SRAM exhibits data remanence, but it is still volatile in the conventional sense that data is eventually lost when the memory is not powered.
SRAM is also used in personal computers, workstations, routers and peripheral equipment: CPU register files, internalCPU caches and external burst mode SRAM caches, hard disk buffers, router buffers, etc. LCD screens and printersalso normally employ static RAM to hold the image displayed (or to be printed).
The traditional spinning hard drive (HDD) is the basic nonvolatile storage on a computer. That is, it doesn’t “go away” like the data on the system memory when you turn the system off. Hard drives are essentially metal platters with a magnetic coating. That coating stores your data, whether that data consists weather reports from the last century, a high-definition copy of the Star Wars trilogy, or your digital music collection. A read/write head on an arm accesses the data while the platters are spinning in a hard drive enclosure.
An SSD does much the same job functionally (saving your data while the system is off, booting your system, etc.) as an HDD, but instead of a magnetic coating on top of platters, the data is stored on interconnected flash memory chips that retain the data even when there’s no power present. The chips can either be permanently installed on the system’s motherboard (like on some small laptops and netbooks), on a PCI/PCIe card (in some high-end workstations), or in a box that’s sized, shaped, and wired to slot in for a laptop or desktop’s hard drive (common on everything else). These flash memory chips differ from the flash memory in USB thumb drives in the type and speed of the memory. That’s the subject of a totally separate technical treatise, but suffice it to say that the flash memory in SSDs is faster and more reliable than the flash memory in USB thumb drives. SSDs are consequently more expensive than USB thumb drives for the same capacities.
The internal cable interface has changed from Serial to IDE to SCSI to SATA over the years, but it essentially does the same thing: connects the hard drive to the PC’s motherboard so your data can be processed. Today’s 2.5- and 3.5-inch drives use SATA interfaces almost exclusively (at least on most PCs and Macs). Capacities have grown from multiple megabytes to multiple terabytes, an increase of millions fold. Current 3.5-inch HDDs max out at 4TB, with 2.5-inch drives at 2TB max.
Fragmentation: Because of their rotary-like recording surfaces, HDD surfaces work best with larger files that are laid down in contiguous blocks. That way, the drive head can start and end its read in one continuous motion. When hard drives start to fill up, large files can become scattered around the disk platter, which is otherwise known as fragmentation. While read/write algorithms have improved where the effect in minimized, the fact of the matter is that HDDs can become fragmented, while SSDs don’t care where the data is stored on its chips, since there’s no physical read head. SSDs are inherently faster.
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In computing, DDR3 SDRAM, an abbreviation for double data rate type three synchronous dynamic random access memory is a modern type of dynamic random access memory (DRAM) with a high bandwidth (“double data rate“) interface, and has been in use since 2007. It is the higher-speed successor to DDR and DDR2 and predecessor to DDR4 synchronous dynamic random access memory (SDRAM) chips. DDR3 SDRAM is neither forward nor backward compatible with any earlier type of random access memory (RAM) due to different signaling voltages, timings, and other factors.
The primary benefit of DDR3 SDRAM over its immediate predecessor, DDR2 SDRAM, is its ability to transfer data at twice the rate (eight times the speed of its internal memory arrays), enabling higher bandwidth or peak data rates. With two transfers per cycle of a quadrupled clock signal, a 64-bit wide DDR3 module may achieve a transfer rate of up to 64 times the memory clock speed megahertz (MHz) in megabytes per second (MB/s). With data being transferred 64 bits at a time per memory module, DDR3 SDRAM gives a transfer rate of (memory clock rate) × 4 (for bus clock multiplier) × 2 (for data rate) × 64 (number of bits transferred) / 8 (number of bits/byte). Thus with a memory clock frequency of 100 MHz, DDR3 SDRAM gives a maximum transfer rate of 6400 MB/s. In addition, the DDR3 standard permits DRAM chip capacities of up to 8 Gbit.