Hard Disk Drive & Solid State Drive

Hard Disk Drive

Note: I merged two informational articles into a single page. I thought this was necessary because the relation between a HDD and SSD are very close.


A hard disk drive (HDD) is a storage device usually taking the form of a rectangular box typically inside a computer. It is used to store and retrieve data by using magnetic disk/platters coated with magnetic material. Unlike Random Access Memory, a HDD can keep its memory even when not supplied with power. Data storage/retrieval algorithms are very similar to RAM however, since data are stored/retrieved in any order, creating the problem of file fragmentation the user has to take care of ever so rarely. Data is stored on the rotating disks/platters and magnetic heads on an actuator arm that barely makes contact with the disk supplies and retrieves information that is needed.


The first hard drive was created by IBM in 1956 for a real-time transaction processing computer and developed for mainframe and minicomputers. The first IBM drive was the 350 RAMAC. It was the size of two refrigerators and stored 3.75 megabytes on a stack of 50 disks. In 1961, IBM introduced model 1311, which was the size of a washing machine and stored 2 megabytes on a removable disk pack. This was meant so that users could buy more packs and change them when needed. Later models of removable pack drives became the dominant storage medium in most computers and reached capacities of 300 megabytes in the 1980’s. Then non-removable HDDs were called ‘fixed disk drives’.

In 1973, IBM introduced a new type of HDD codenamed “Winchester”. Rather than not having the disk heads not withdrawn completely from the stack of disk platters when a drive is powered down, the heads allowed to land on a special area of the disk surface upon spin-down. This allowed the drive to take off again where the disk was later powered on, and heavily lowered the cost of the actuator mechanism.

Now into the late 1980’s, Hard Disk Drives became much more cheaper and were found on almost every single decent computer. During the beginning decade, they were found expensive and were sold as an extra component that the buyer can choose to have. Apple Macintosh computers was one of the first to include external hard disk drives, in which every Mac between 1986 to 1998 included a SCSI adapter on the back ports.

The hard drive truly became the main dominant secondary storage (any storage device for storing information that is not needed for a fully functioning system) for a general purpose computer since the early 1960’s. HDDs improved in terms of speed (revolutions per minute), data capacity (megabytes to gigabytes, and now terabytes), and reliability plus transfer speed (SATA 1, 2 and 3). Hard Drives are now the primary storage medium used in servers and personal computers. Although, a couple hundred companies have produced HDD in the past, the main manufacturers are notably Western Digital, Seagate and Toshiba.


The primary technicalities for a HDD are its storage capacity and performance. Capacity was once only in its megabytes when first introduced, but much larger than the floppy diskette. Capacity are usually in prefixes to the power of a 1000. Examples include 1 terabyte (TB) being a capacity of 1,000 gigabytes (or specifically, 1,024 gigabytes).Now, a standard hard drive to be found in a terabyte or more. Some of a HDD’s storage capacity are unusable to the user because of the file system/system swap being used by the operating system and the built in tables of a hard drive which allows technicians and data recovery specialists to recover deleted data that hasn’t been already written over yet.

Performance is specified by the time it takes to move the heads to a file (Average Access time) and the time for the file to move under its head (average latency, which is the physical rotational speed of the metallic platters, measured in Revolutions Per Minute) at which the speed of the file is transmitted (data transfer rate, measured by a SATA generation of 1 for 1.5 gigabits per second, 3 gigabits per second or 6 gigabits per second).

There are different from factors in Hard Drives, but the two most common ones used in modern day computers are 3.5-inch (for desktops) and 2.5-inch (for laptops). HDDs are connected to systems by an interface cable such as a SATA generation 1 (1.5 gigabits per second), 2 (3 gigabits per second) and 3 (6 gigabits per second). Cables also include USB commonly used for external hard drives and SAS (serial attached SCSI) cables used in older models.


A Vertex 2 Solid State Drive (SSD) by OCZ A SSD is an electronic disk, extremely similar to how flash memory works but are used in actual personal computers, competing against the high capacity Hard Disk Drive. Instead of using motors, platters or any physical moving components to store and retrieve data, the Solid State Drive uses flash memory (integrated circuits) to store and retrieve information. While USB flash drives have non-moving parts like the SSD used as a permanent drive inside a computer does, a USB drive is meant to be used on multiple computers, require less power and are much slower due to transfer rates with USB. Solid State Drives also uses no magnetic material to store data, opposing to Hard Drive platters and Floppy Disks. They still use similar algorithms that Hard Disk Drive uses, like being compatible with the same SATA generation 1, 2 or 3 cables.

Advantages to use a SSD are very plentiful. This includes greater durability to physical shock (due to no moving parts), runs much more silent (once again, no moving parts), very low access time and latency (did I say no moving parts?).

Disadvantages with SSDs includes a limited amount of writes, so transferring large mass amounts of files constantly might be a problem. They are also extremely expensive per gigabyte. An example includes a one terabyte hard disk drive costing 65$, while a 128 gigabyte Samsung 840 pro SSD (2014) costs 120$. This is roughly 6 to 8 times more expensive per unit of storage than a hard drive.


One of the earliest SSDs used in practical applications was used in the Psion MC 400 Mobile Computer. It had four slots just meant for Solid State Drives. The SSD wasn’t popular since it was seen very similar to RAM (it could not retain data), but manufacturers during the 90’s continued to improve the technology. In 1995, the company, M-Systems, created one of the first flash based Solid State Drives (non-volatile memory). They were not as fast as other DRAM drives applications, but replaced Hard Disk Drives to be used extensively in military and aerospace engineering due to their extreme durability, vibration, temperature ranges and reliability. SSDs also have the mean time between failures (MTBF) rates that a usual Hard Drive cannot come close to when paired with one.

Soon later, the SSDs began to make their way to public when manufacturers started producing cheaper, more faster drives. OCZ technologies in 2009 introduced a 1 terabyte SSD drive connecting to PCI-e slots on a motherboard that was meant to be used in Enterprise Computers. SSDs in current days are much more cheaper, more reliable than ever and provide enough capacity to hold to how much a Hard Disk Drive halved can hold.


At first, SSDs used DRAM type memory. Since 2010, SSDs after that now use NAND type flash memory. This is a specific type of memory that allows data to be retained even when powered off thus, non-volatile memory can be achieved. SSDs may be created by using multiple Random Access Memory Modules also. It was also created so that the price per bit could be much cheaper and more capacity could hold on a much smaller scale. NAND flash memory can be found literally on any electrical device that requires temporary, permanent or usable storage that doesn’t require physical moving parts.

Hybrid drives are computer secondary storage medium that incorporates a Hard Drive Disk along with the integrated circuits of a Solid State Drive. This allows large amounts of data to be stored on the actual Hard Disk portions of the drive, while data that are required to be accessed fast (the operating system) are stored on the Integrated Circuit portion of the drive.


Almost all modern SSDs comes with controllers to help bridge the NAND flash memory chip to the computer itself. It features its own processing unit to help execute firmware code for the primary functions of the SSD. Controllers can include:

  • Error-correcting code (ECC)
  • Wear Leveling
  • Read and write caching
  • Encryption

While NAND itself is much slower than actual DRAM modules, this was corrected by controllers. Different type of architectures also came out for different SSD drives. Multi Level Cell is a type of flash memory where more data can be stored per cell using the same number of transistors compared to other architectures. MLC NAND has four states per cell, so two bits per cell is possible. MLC was designed for low error rates, making it ideal for reliability and use in company enviornments. Single Level Cell is when memory are stored in individual memory cells made out of transistors. This has the advantage of faster write speeds, lower power consumption and higher cell endurance. Because SLC stores less data than MLC, it costs more per megabyte. SLC is mainly used in high-performance memory card because of the faster transfer speeds and longer life span.

Computers | Hardware

QR Code
QR Code hdd_and_ssd (generated for current page)