Key facts

  • In 1945, John von Neumann described the stored-program idea: instructions and data can both reside in memory, which became the basis of most modern co...
  • In 1947, the Williams-Kilburn tube demonstrated an early random-access electronic memory, showing that a machine could read and write stored bits quic...
  • In 1956, IBM introduced the IBM 350 disk storage unit with the RAMAC system, making magnetic disk storage a practical secondary-storage technology.
  • In 1968, Robert H. Dennard of IBM received a patent for one-transistor DRAM, the memory cell design that still underlies main memory chips.
  • In 1982, the Compact Disc became a commercial optical storage medium, using laser reading rather than magnetic heads.

Key Points at a Glance

  1. 1

    In 1945, John von Neumann described the stored-program idea: instructions and data can both reside in memory, which became the basis of most modern computers.

  2. 2

    In 1947, the Williams-Kilburn tube demonstrated an early random-access electronic memory, showing that a machine could read and write stored bits quickly.

  3. 3

    In 1956, IBM introduced the IBM 350 disk storage unit with the RAMAC system, making magnetic disk storage a practical secondary-storage technology.

  4. 4

    In 1968, Robert H. Dennard of IBM received a patent for one-transistor DRAM, the memory cell design that still underlies main memory chips.

  5. 5

    In 1982, the Compact Disc became a commercial optical storage medium, using laser reading rather than magnetic heads.

  6. 6

    In 1984, Fujio Masuoka at Toshiba presented flash memory, giving computers and devices non-volatile semiconductor storage.

  7. 7

    In 1996, the first Universal Serial Bus standard was released, helping make plug-and-play external storage devices common.

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Basic memory ideas and units

Computer memory stores data, instructions and intermediate results in binary form. The smallest unit is a bit, which can hold 0 or 1. Eight bits make one byte, and bytes are grouped into larger units such as kilobyte, megabyte, gigabyte and terabyte. In exam questions, remember that computer memory is often counted in powers of 2: 1 KB is commonly treated as 1024 bytes, 1 MB as 1024 KB, 1 GB as 1024 MB and 1 TB as 1024 GB. Storage companies may also use decimal marketing units, but objective papers usually test the binary ladder.

Two terms often confuse candidates: capacity and speed. Capacity means how much data a device can hold; speed means how fast it can read or write. Latency is the delay before data transfer begins, while bandwidth or data transfer rate is the amount moved per second. Volatile memory loses contents when power is switched off; non-volatile memory retains contents without power. Memory can also be random access, where any location can be reached directly, or sequential access, where data is reached in order.

Exam takeaway: memorise bit, nibble, byte, KB, MB, GB and TB, and separate capacity, latency, bandwidth, volatility and access method.

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