A Survey of Storage Options

42 Computer A Survey of Storage Options I f you were a personal computing enthusiast in 1984, you could buy an IBM PC for $5,000 to $6,000—about $8,000 to $9,500 in today's currency. For this you would get a 0.004-GHz 8-bit processor with 0.064 Mbytes of RAM, a 12-inch monochrome text-only display, a 0.16-Mbyte floppy drive, and no possibility of a hard drive. Compare that with a PC purchase today: a 2-GHz 32-bit processor with 2,000 Mbytes of RAM, a 128-Mbyte video graphics card, a 700-Mbyte CD-RW (and maybe a DVD-R), a 17-inch 1600 × 1200 display with 32 million colors—all for maybe $1,500. The old machine cost six times as much for 1/2000th of the processing power. The purchasing power gain over 18 years is 1,200,000 percent. Very few industries have shown such dramatic increases in value and function and simultaneous reductions in cost as the computer storage industry. The technology has evolved continuously over the past 50 years both across different media and within each one. We can categorize primary storage as volatile random access memory, which loses its data upon power loss, and nonvolatile memory, such as flash and read-only memories, in which data persists. Data transfer forms include floppy disks, CDs, DVDs, and flash memory cards. Fast random access forms include disk drives, flash memory, and the slower DVD-RAM. Data archive forms include tape, CD, and DVD. The two basic types of RAM are dynamic RAM and static RAM. IBM's Robert H. Dennard created the one-transistor, small-capacitor DRAM in 1966. In 1970, Fairchild Corp. invented the first 256-Kbyte SRAM; by 1972 it was the best-selling semiconductor memory chip in the world, superseding the magnetic core memories that computers had used since 1947. Both types of RAM are volatile—they lose their contents when the power shuts down. DRAM requires thousands of refreshes per second. SRAM is faster because it does not need to be refreshed. If all things were equal, main memory would use SRAM, since it is faster than DRAM and does not require refresh circuitry to protect data from corruption. However, SRAM is physically larger than DRAM and it costs considerably more, making it impractical for main memory, although it is still useful for relatively small caches. Asynchronous and synchronous DRAM. DRAM can be either asynchronous or synchronous. With an asyn-chronous interface, the processor must wait idly for the DRAM to complete its internal operations, …