The history of Storage

Storage

Storage persistently stores and retrieves data. Storage systems store data blocks than can be retrieved either as raw data or as files. Persistency in storage means that data stored on a storage device remains on it, even without supplied power.

Early storage systems

The earliest computers used no persistent storage system. When these first computers were switched on, using manual switches some instructions were loaded in main memory and executed. These instructions instructed the computer to load a program in main memory from a paper tape or from punched cards. Output was printed on paper. Data was stored on paper tape or punched cards, leading to typical batch processing systems, where the output from one step was fed as input into the next step.

Drum memory

Drum memory was one of the first magnetic storage systems. It was widely used in the 1950s and into the 1960s. For many computers, a drum formed the main working memory of the machine. Drums were so commonly used as computer’s main memory that these computers were often referred to as drum machines.

Drum memory consists of a large metal cylinder that was coated on the outside surface with a ferromagnetic recording material. It could be considered the precursor to the hard disk platter, but in the form of a drum rather than a flat disk. In most cases multiple rows of fixed read-write heads were placed along the long axis of the drum, one head for each track on the drum.

A difference between a drum as described and a modern disk is that on a drum the heads do not have to move to the track to access; the controller simply waits for the data to appear under the relevant head as the drum turns. In a disk drive the head takes a certain time, the seek time, to move into place, while the performance of a drum with fixed heads is determined almost entirely by the rotational speed.

Hard disks

A computer disk consists of a set of rotating disk platters and magnetic read/write heads mounted on a movable arm. This allows the read/write heads to reach any place on the disk.

The disk platters are covered with high density magnetic material that allows the storage of data by magnetizing the particles in two directions (representing 0's and 1's).

The first commercial digital disk storage device, was the IBM RAMAC 350 shipped in 1956. It could store a whopping 4.4 MB of data! It was composed of fifty 24-inch (61 cm) diameter disks. The system was 60 inches (152 cm) long, 68 inches (172 cm) high and 29 inches (74 cm) deep and it weighed over a ton.

IBM 1311 Disk Storage Drive was announced in 1962 as being the first disk drive with a removable disk pack. Each pack weighed about ten pounds, held six disks, and had a capacity of 2 MB.

In 1980 Seagate Technology created the first hard disk drive for microcomputers (called the ST506). The disk could store 5 MB, which was five times as much as a standard 5 ¼" floppy disk at that time. In the mean time drive systems had shrunk to fit in the space of a 5 ¼" floppy disk drive. Upon releasing its first product, Seagate quickly drew such big- name customers as Apple Computer and IBM. Within a few years, it had sold 4 million units, making Seagate the market leader for small size hard disk drives.

Since the introduction of the RAMAC 350 disk sizes shrunk and disk capacity raised every year. Storage predictions show the historic average disk size since 1980 and a projection for the next years.

This picture shows that the average disk capacity has followed a logarithmic increase in size for the last 30 years (be aware that the Y-axis is logarithmic instead of linear). Kryder's law states that "the density of information on hard drives has been growing at a rate, increasing by a factor of 1000 in 10.5 years, which corresponds to a doubling roughly every 13 months".

Floppy disks

In 1971 IBM invented the 8-inch floppy diskette. It quickly won widespread acceptance as a program and data-storage medium. Unlike hard drives, a user could easily transfer a floppy from one drive to another.

The 5 ¼" flexible disk drive and diskette were introduced by Shugart Associates in 1976. This was the result of a request by Wang Laboratories to produce a disk drive small enough to use with a desktop computer, since 8" floppy drives were considered too large for that purpose.

5 ¼" floppy drives were used in the first IBM PCs and their clones. A disk could store 360KB of data, which was more than enough at the time since the PCs only had 64KB of main memory. Since the original IBM PC did not include a hard disk drive, the 5 ¼" floppy was the only available persistent storage media (apart from the analogue tape connection of course).

Sony introduced and shipped the first 3.5" floppy drives and diskettes in 1981. These floppy disks became very popular as they had a reasonable capacity of 1.44 MB and a very attractive form factor. The hard cover also made the disks more robust than the previous 8" and 5 ¼" floppies. IBM started to use 3.5" floppy drives in their PS/2 line of products, after which many others followed. This effectively stopped the use of 5 ¼" floppies in just a few years.

Nowadays floppy drives are mostly replaced by USB based storage (flash disk drives).

Tape drives

Magnetic tape allows for inexpensive mass storage of information. The IBM 726, announced in 1952 was one of the first practical magnetic tape systems. The Model 726 could store 2 million digits per tape—an enormous amount at the time. The system used a unique ‘vacuum channel’ method of keeping a loop of tape circulating between two points allowing the tape drive to start and stop the tape in a split-second.

In 1984 IBM announced the 3480 cartridge tape system that was to replace the traditional reels of magnetic tape with a 4” x 5” (10 x 12 cm) cartridge that could store 200MB of data. Other computer makers began making 3480- compatible storage systems for several years after that, offering increased storage capacity in the same physical format.

In 1987 Exabyte and Sony introduced Helical scan tape drives. These tape drives used a rotating drum with multiple read/write heads spinning round the tape in a specific angle, a technology also used in Video Tape Recorders (VCRs).

This allowed for a much more efficient use of the overall surface of the physical tape, increasing the capacity of the tape. Due to the complex and delicate technology Helical drives were very expensive and were not widely used.

In 1984 DEC introduced the Digital Linear Tape (DLT) drive. DLT drives could store up to 20GB of data on a tape with a small form factor. The tape medium could be made small because the tape housing contained only one reel. The other reel was located in the DLT drive unit.

A variant with higher capacity is called Super DLT (SDLT), which can store up to 300GB.

Linear Tape Open (or LTO) is originally developed in the late 1990s as an open standards alternative to the proprietary magnetic tape formats that were available at the time. The standard form-factor of LTO technology goes by the name Ultrium, the original version of which was released in 2000 and could hold 100 GB of data in a single cartridge. The most recent version was released in 2010 and can hold 1.5 TB in the same size cartridge.

LTO cartridges look similar to DLT cartridges and have roughly the same size, but they are not interchangeable. Both (S)DLT and LTO are still in use today.

Optical storage

Data can be stored on an optically readable medium. The best known examples of this are the CD-ROM, DVD or Blu-ray disk. The medium is spinning and a small laser beam reads microscopic pits in the disk. The pits represent data (0's and 1's).

Laserdisc technology, using a transparent disc, was already invented in 1958. Laserdisc used a light source behind the rotating disk showing information on the disk to a transducer head that read it on the opposite side of the disk.

By 1969 Philips had developed a videodisc in reflective mode, which has great advantages over the transparent mode, since it could be read by a laser and could store a much higher density of information. MCA and Philips first publicly demonstrated the videodisc in 1972, which could be used to show video on a TV. Laserdisc was first available on the market in 1978, two years after the VHS VCR and four years before the CD, which is based on Laserdisc technology.

The 1985 “Yellow Book” standard developed by Sony and Philips adapted the CD format to hold any form of binary data. It led to the introduction of CD-ROMs, rewritable media like CD-RW, and many other formats.

When CD-ROMs were introduced they had more capacity than computer hard drives common at the time. The reverse is now true, where hard drive capacity far exceeds that of CDs, DVDs and Blu-ray disks.

CD-ROM drives were rated with a speed factor relative to music CDs (1× or 1- speed which gives a data transfer rate of 150 Kbit/s and would take about an hour to read a complete CD). Around 1997, 12× drives became common. Above 12× speed, there are problems with vibration and heat of CD-ROMs.

CD-ROMs and DVDs were mostly used to distribute software. Previously this was done using floppy disks, but the size of applications made this impractical at some point (Novell NetWare for instance shipped on 25 floppy disks that had to be loaded one-by-one, some needed to be loaded even multiple times for configuration reasons).

Nowadays rewritable DVDs are the standard (storing up to 4 GB of data on a single layer), soon to be replaced by Blu-ray disks, capable of storing 20GB.


This entry was posted on Zaterdag 23 Oktober 2010

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