In the early days of computers efficient, fast, and reliable
mechanisms for storing data were basically unknown and mostly had
to be invented from scratch.
Ideally the me…mory should involve a minimum of electronics, permit
random access anywhere in the same period of time, and require
little maintenance to prevent data corruption in operation at a
relatively low cost per memory location. However given the state of
electronics at the time, there were many aspects of these
requirements that conflicted.
Sequentially accessed memories are much simpler, reliable, and
lower cost than randomly accessed memories but access time is
variable and usually longer than randomly accessed memories.
Therefore many early computers used various types of sequentially
accessed memory: rotating capacitor drum dynamic memory, mercury
tank acoustic wave delay line dynamic memory, rotating multiple
fixed head magnetic drum memory, rotating multiple fixed head
single platter magnetic disk memory, magnetostrictive delay line
dynamic memory, etc.
The early randomly accessed memories were all based on vacuum
tubes: Williams-Kilburn tube (CRT) dynamic memory, various type of
"flood gun" CRT static memories, Selectron tube static memory, etc.
However these systems either had high maintenance costs or
manufacturing the special vacuum tubes (e.g. Selectron tubes)
The first truly practical randomly accessed memory system developed
used ferrite magnetic cores. This was not only static but also
nonvolatile memory, thus offering significant advantages over
earlier memories. Ferrite magnetic core memories rapidly replaced
all earlier computer memory systems (except in the very lowest cost
systems where very low cost sequentially accessed memories
continued in use), and dominated the computer main memory and
buffer memory markets for over 20 years.
Intel developed the semiconductor DRAM (i.e. the 1103) in 1970, a
randomly accessed solid state dynamic memory chip. By about 1975
various semiconductor DRAM chips had replaced all earlier computer
main memory types. The cost per bit was very low and has continued
to drop, while memory sizes have essentially grown exponentially
In terms of bulk storage (often offline, requiring operator action
to make it available to the computer), many early computers used
decks of punchcards or rolls of punched paper tape, but these were
slow and the paper could wear out over time becoming unreadable.
Magnetic tape was introduced on the UNIVAC i (i.e. nickel plated
bronze strip) in 1951 and IBM 701 (i.e. iron oxide coated cellulose
acetate strip) in 1952 which was much faster, higher data capacity,
and more reliable than the punchcard or paper tape storage.
IBM introduced the first movable head magnetic hard disk (i.e. the
IBM 350) in 1956, this has gone through many improvements since
then and in various forms now dominates most of bulk data storage
Photostore optical memory was the first bulk storage with a
capacity exceeding one billion bits, however it involved large
complex high maintenance mechanical systems to write and read the
small film cards the data was recorded on.
Digital CDs and DVDs have been used for ROM for several years, but
writable ones are also available.
Semiconductor Flash memories were introduced in the 1990s and
although originally only used as electronically reprogrammable ROM,
improved versions are now beginning to replace magnetic hard disks.
There are also many other things that have been tried as memories
over time, with varying degrees of success (and frequently
failure), but listing all of these would be far beyond the scope of
this site and would involve writing several books. Many of them are
"minor" variants on systems mentioned above. (MORE)