Studying the history of disks is the beginning of the path to understanding the principles of operation of solid state drives. The first part of our series of articles "Introduction to SSD" will take a digression into history and allow you to visually understand the difference between the SSD and its closest competitor - HDD.
Despite the abundance of various devices for storing information, the popularity of HDD and SSD in our time is undeniable. The difference between these two types of drives is obvious to the average person: SSD is more expensive and faster, while HDD is cheaper and more spacious.
Special attention should be paid to the unit of storage capacity: historically, decimal prefixes, such as kilo- and mega-, in the context of information technology mean both the tenth and twentieth powers of two. To eliminate confusion, binary prefixes kibi-, mebi- and others were introduced. The difference between these set-top boxes becomes noticeable with increasing volume: buying a 240 gigabyte disk, you can store 223.5 gigabytes of information on it.
Immersion in history
The development of the first hard drive has been carried out since 1952 by IBM. On September 14, 1956, the final development result was announced - the IBM 350 Model 1. The drive contained 3.75 mebibytes of data with very immodest dimensions: 172 centimeters high, 152 centimeters long and 74 centimeters wide. Inside were 50 thin disks covered with pure iron, 610 mm (24 in) in diameter. The average disk search time was ~600 ms.
As time went on, IBM steadily improved the technology. In 1961 presented with a capacity of 18.75 megabytes with read heads on each plate. IN removable disk cartridges appeared, and since 1970, an error detection and correction system has been introduced into the IBM 3330. Three years later appeared known as "Winchester".
Winchester (from English Winchester rifle) - the general name for rifles and shotguns produced by the Winchester Repeating Arms Company in the USA in the second half of the XNUMXth century. These were one of the first repeating shotguns that gained immense popularity among buyers. They owe their name to the company's founder, Oliver Fisher Winchester.
The IBM 3340 consisted of two spindles of 30 MiB each, due to which engineers called this disc "30-30". This name was reminiscent of the Winchester Model 1894 rifle chambered in .30-30 Winchester, which led Kenneth Haughton, who led the development of the IBM 3340, to say "If it's 30-30, then it must be Winchester" ("If it's a 30-30, then it must be a Winchester."). Since then, "hard drives" have been called not only rifles, but also hard drives.
Three years later, the IBM 3350 "Madrid" came out with 14-inch platters and 25 ms access time.
The first SSD was created by Dataram in 1976. The Dataram BulkCore drive consisted of a chassis with eight 256 KiB RAM sticks. Compared to the first hard drive, BulkCore was tiny: 50,8 cm long, 48,26 cm wide and 40 cm high. At the same time, the data access time in this model was only 750 ns, which is 30000 times faster than that of the most modern HDD at that time.
In 1978, Shugart Technology was founded, which a year later changed its name to Seagate Technology in order to avoid conflicts with Shugart Associates. Two years later, Seagate launched the ST-506, the first hard drive for personal computers in a 5.25-inch form factor with a capacity of 5 MiB.
In addition to the appearance of Shugart Technology, 1978 was remembered for the release of the first Enterprise SSD from StorageTek. The StorageTek STC 4305 held 45 MiB of data. This SSD was designed as a replacement for the IBM 2305, was similar in size and cost an incredible $400.
In 1982, the SSD enters the personal computer market. Axlon is developing a RAM-chip SSD specifically for the Apple II called RAMDISK 320. Since the drive was created on the basis of volatile memory, a battery was included in the kit to maintain the safety of information. The battery capacity was enough for 3 hours of battery life in case of power failure.
A year later, Rodime will release the first 352 MiB RO10 hard drive in a 3.5-inch form factor that is familiar to the modern user. Despite being the first commercial drive in this form factor, Rodime hasn't really done anything innovative.
The first product in this form factor is the floppy drive introduced by Tandon and Shugart Associates. Moreover, Seagate and MiniScribe agreed to adopt the 3.5-inch industry standard, "leaving out" Rodime, which was waiting for the fate of the "patent troll" and a complete exit from the storage industry.
In 1980, Toshiba engineer Professor Fujio Masuoka filed a patent for a new kind of memory called NOR flash memory. Development took 4 years.
NOR memory is a classic 2D wire matrix, in which one cell is installed at the intersection of rows and columns (analogous to memory on magnetic cores).
In 1984, Professor Masuoka spoke about his invention at the International Electronics Developers Meeting, where Intel quickly appreciated the prospects of this development. Toshiba, where Professor Masuoka worked, didn't think Flash was anything special, so they agreed to Intel's request to make some prototypes to study.
Intel's interest in developing Fujio prompted Toshiba to assign five engineers to help the professor solve the problem of commercializing the invention. Intel, in turn, sent three hundred employees to create their own version of Flash-memory.
While Intel and Toshiba were developing flash drives, two important events occurred in 1986. First, SCSI, a set of agreements for interaction between computers and peripherals, has been officially standardized. Secondly, the AT Attachment (ATA) interface, known under the brand name Integrated Drive Electronics (IDE), has been developed, thanks to which the disk controller has moved inside the disk.
For three years, Fujio Mausoka worked on improving Flash memory technology and by 1987 had developed NAND memory.
NAND memory - the same NOR memory, organized in a three-dimensional array. The main difference is that the algorithm for accessing each cell has become more complex, the cell area has become smaller, and the total capacity has increased significantly.
A year later, Intel developed its own NOR-type Flash memory, and Digipro made a drive called Flashdisk on it. The first version of Flashdisk in the maximum configuration contained 16 MiB of data and cost less than $500
In the late 80's and early 90's, hard drive manufacturers competed to make drives smaller. In 1989, PrairieTek releases the 220 MiB PrairieTek 20 disk in a 2.5-inch form factor. Two years later, Integral Peripherals creates the Integral Peripherals 1820 "Mustang" disc with the same volume, but already 1.8 inches. A year later, Hewlett-Packard reduced the disk size to 1.3 inches.
Seagate stayed true to the 3.5-inch drive and bet on speed, with the release of its famous Barracuda in 1992, the first 7200 rpm hard drive. But Seagate wasn't going to stop there. In 1996, Seagate Cheetah drives reached 10000 rpm, and four years later, the X15 modification was spinning up to 15000 rpm.
In 2000, the ATA interface became known as PATA. The reason for this was the appearance of the Serial ATA (SATA) interface with more compact wires, hot-swap support and increased data transfer rates. Seagate took the lead here too, releasing the first hard drive with this interface in 2002.
Flash memory was initially very expensive to manufacture, but the cost dropped dramatically in the early 2000s. This was taken advantage of by Transcend, which in 2003 released SSDs ranging from 16 to 512 MiB. Three years later, Samsung and SanDisk joined mass production. In the same year, IBM sells its disk division to Hitachi.
Solid state drives were gaining momentum and there was an obvious problem: the SATA interface was slower than the SSDs themselves. To solve this problem, the NVM Express Workgroup began developing NVMe, a specification for protocols for accessing SSDs directly via the PCIe bus, bypassing the “intermediary” in the form of a SATA controller. This would allow access to data at the speed of the PCIe bus. Two years later, the first version of the specification was ready, and a year later the first NVMe drive appeared.
Differences between modern SSDs and HDDs
At the physical level, the difference between SSD and HDD is easily noticeable: there are no mechanical elements in the SSD, and information is stored in memory cells. The absence of moving elements leads to fast access to data in any part of memory, however, there is a limit on the number of rewriting cycles. Due to the limited number of rewriting cycles for each memory cell, there is a need for a balancing mechanism - leveling out the deterioration of cells by transferring data between cells. This job is done by the disk controller.
To perform balancing, the SSD controller needs to know which cells are occupied and which are free. Writing data to a cell, the controller is able to track itself, which cannot be said about deletion. As you know, operating systems (OS) do not erase data from the disk when the user deletes a file, but mark the corresponding memory areas as free. This solution eliminates the need to wait for a disk operation when using an HDD, but is completely unsuitable for SSD operation. The SSD disk controller works with bytes, not file systems, and therefore requires a separate file delete message.
This is how the TRIM command appeared (English - trim), with which the OS notifies the SSD disk controller about the release of a certain area of \uXNUMXb\uXNUMXbmemory. The TRIM command permanently erases data from the disk. Not all operating systems are aware of the need to send this command to SSDs, and hardware RAID controllers in disk array mode never send TRIM to disks.
To be continued ...
In the following parts, we will talk about form factors, connection interfaces, and the internal organization of solid state drives.
In our laboratory You can independently test modern HDD and SSD drives and draw your own conclusions.
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Do you think SSD can replace HDD?
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71.2%Yes, SSD is the future
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7.5%No, the era of magneto-optical HDD42 is ahead
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21.2%HDD + SSD118 hybrid variant will win
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Source: habr.com