SciFact: Advances in Data Storage for Personal Computers

In the beginning was the paper tape,

and it was horrible. Tape punches were noisy, tape readers were slow (about 10 characters per second, or 100 bits per second), paper tape was fragile and prone to disintegrate even without being abused. And yet it was vastly better than toggling a program in on the front panel, 8 or (if you were one of the privileged few) 16 bits at a time; you could use an actual keyboard to punch a tape! A contemporary, used on mainframes and minicomputers, was the punched card stack. Using standard Hollerith code, a fair amount of data, up to 80 characters, could be stored on a single card, and the cardstock was less fragile than paper tape. Woe unto the poor intern who accidentally spilled a tray of carefully-sorted cards, however! Reading them in the correct sequence was critical to the success of a program. To this end, entire machines, larger than a large chest freezer, were dedicated to doing nothing except sorting cards. The only effective size limit on storing data on punched tape or cards was the size of the room where you kept them; but since 64 k (that’s right, kilobytes, not megabytes or gigabytes) of computer memory was still an incredible amount of RAM, individual tapes and cards stacks remained fairly small.

Soon after came magnetic tape and cards. The magnetic cards were used by mainframes and minis again; huge tape drives began to appear for mass storage of data on those machines. By this time, the “glass teletype” (CRT terminal, with full keyboard) had become affordable enough that many PC owners had their own, and some clever fellows figured out how to store data on cassette tapes using an audio code. A plethora of methods were in use at first, but the Kansas City Standard soon triumphed over all others around 1975, and before long you could swap tapes with your friends and have a reasonable expectation that you could read one another’s data most of the time. Floppy disk drives were available by this time, but at over $1000 each, they were not found attached to many PCs. The KCS tapes could read and write data at 300 baud; a later variation increased the speed to 1200 baud. At the time, “baud” was effectively the same as “bits per second.” For contrast, a modern dial-up modem can connect at up to 51.5 kbps (thousand bits per second), or almost 172 times as fast, and a “slow” DSL connection at 128 kbps is over 425 times as fast. Consumer fiber optic and cable modem connections routinely achieve 5 megabits per second (5 million bps) and higher, which is over 16 thousand times as fast as the original KCS tapes. A standard 120-minute tape (60 minutes per side) could hold a whopping 1.08 megabits, or about 108 kilobytes of data at 300 bps.

The next generation of PCs to come along, and the first to be really accessible to anyone other than the hobbyist, started with the Commodore PET, which had a built-in cassette drive, followed soon after by the Commodore 64 and Atari 800 series PCs. These powerful 8-bit machines had a “serial bus” connector, the ancient precursor to today’s USB ports, and were able to be connected to tape drives and the first widely-affordable (at somewhere under $1000) floppy disk drives. The floppy drives themselves were about the same size and weight of a modern small form factor PC like the Dell Optiplex SX280, and were able to store a whopping 90 kilobytes on each side. Like vinyl record albums, both sides could be used (if the disk manufacturer had coated both sides with magnetic media, and if the “write-enable hole” existed for both sides). The Commodore drives can been seen in this article at the C64 Wiki; they were limited in speed to about 300 bytes/second, or 3k bps (only 10 times the speed of the KCS tapes), due to a design flaw in the original serial chip. User modifications came along later that cranked the speed up to about 10K bytes/second. The Atari serial bus was capable of 19.2Kbps without modification, a full 64 times the speed of the KCS tapes, and more than 6 times the speed of the C64 floppy drives. Atari 8-bit users frequently taunted their C64-using friends over this speed difference, but in truth, both sets of users normally started a program load from disk and went to get a beverage while they waited for the load to complete.

Hard disk drives (HDD) were introduced by IBM in 1956 (Source: Wikipedia) but remained out of the average consumer’s reach due to price until after 1980, when Seagate Technology introduced the ST-506, the first 5.25-inch hard drives, with a formatted capacity of 5 megabytes. Aside from speed considerations (which are seriously important by the time you get into millions of bytes of data), the ST-506 had more than 27 times the storage space of a double-sided 5.25-inch floppy disk, and fit into the same width drive bay, although it was twice as high (“full height” indicated a drive that was almost 3.5 inches tall; floppy drives were half-height). Seagate was known at the time for making “bulletproof” hardware, and the ST-506, weighing in at a hefty 2.1 kg (4.6 pounds), lived up to the reputation. Any number of them are to this day being used as doorstops; they are half the size of a cinder block, and nearly as durable (as long as you don’t want to use them for data storage any more).

Advances continued through a number of iterations of smaller floppy drives; standard 3.5-inch drives, at first single sided and later double-sided, but without the need to flip the disk over like the original 5.25-inch disks; “Super floppies” with capacities up to 120 megabytes (compared to the double-sided double-density 1.44 MB 3.5-inch floppy, or the ST-506 with a capacity of 5 MB) appeared, and removable cartridge hard drives made an appearance.

In 1985, the CD-ROM (“compact disk-read only memory”) made the scene (Source: US Byte) and for the first time, consumers were able to get 650 megabytes of data on a single removable (and fairly tough) disk. Speed was tolerable; the first CD drives had a data transfer rate of about 0.15 MB/s. This is called “1X.” Most current drives read data at 48X, or 7.2 MB/s or even faster. This is 240,000 times as fast as the Kansas City Standard! If we had made similar speed advances in privately-owned automobiles, your family car would now be capable of cruising at 1.2 million miles per hour or more; you could drive to the Moon in fifteen minutes.

An incremental improvement in the same laser technology that gave us the CD-ROM also brought us the DVD-ROM, with a capacity of up to 11 gigabytes of data on a single disk.

About 1980, Dr. Fujio Masuoka invented “flash” memory – erasable memory chips that required no power to maintain their data (Source: Wiwkipedia. Initially very expensive and with small data capacities, by the end of the 1980s, every PC contained the BIOS (Basic Input/Output System) in flash chips and the BIOS could be updated without replacing the chips. By the mid-nineties, a number of formats of removable memory cards were beginning to appear on he consumer market; first CompactFlash, then SmartMedia, and soon after Sony’s proprietary MemoryStick, and the now nearly-ubiquitous SecureDigital. Along the way, the Universal Serial Bus (USB) was introduced, and flash chip makers quickly saw the potential for their low-power non-volatile memory; the USB memory stick was a natural invention.

Now, in mid-2009, some 34 years after the introduction of the Kansas City Standard, it’s rare to find someone who doesn’t have at least one computer or a flash-based memory device such as an MP3 player. We are now seeing the beginning of a new sort of revolution in computer data storage: The entire operating system on a removable flash device. Below are two photos of the latest version of the Ubuntu Linux operating system on an SDHC card, 4 gigabytes capacity; that is 4 billion bytes! Less than one-quarter of the card is used for the OS, leaving 3 gigabytes for applications such as OpenOffice and data, such as photos and music.

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Compare the size of the card with my hand in the first photo; SD cards generally measure 32 mm × 24 mm × 2.1 mm. The Seagate ST-506 measured 82.55 mm x 146.05 mm x 203.2 mm, or more than 325,000 times the volume fo the flash card, with only 1/800 the storage capacity. Additionally, the ST-506 required almost 60 watts of power at startup, and typically over 21 watts during normal operation; the flash card requires a maximum of 126 milliwatts, or to put it another way, the ST-506 requires more than 475 times the power of the SD card. You could comfortably read by the light of an old-style 60-watt incandescent bulb; you wouldn’t even notice the bulb in a dark room if it were limited to 126 milliwatts. Even smaller SD cards exist; the mini SD and micro SD card standards exist. SDHC (SD High Capacity) cards are “officially” limited to 32 gigabytes of storage, but the format could theoretically be extended up to 2 terabytes.

Speed comparisons: SD cards routinely achieve 900 kilobytes per second transfer rates, and upwards (cards rated up to 300X, or 45 megabytes per second, are available). That means the slowest SD card will never be slower than 30,000 times the speed of the KCS tape, or roughly twice as fast as the ST-506, which has a maximum transfer rate of 500 kilobytes per send, and is in practice much slower.

Where will we go in the future of computer data storage? I don’t know, but it will be exciting to see! You can count on three things: higher capacity, lower power, and lower cost.

Fun reading for computer history buffs: Binary Dinosaurs

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