Bfh-sts: Created page with "= Memory: From Relays to DRAM = This page traces the evolution of memory technology: how information was stored, from mechanical relays to modern transistor-based RAM. It explains why each step was necessary and what trade-offs were involved. == What Is Memory? == In computer science, '''memory''' is any container that holds a pattern (0/1) until it is changed. * Everyday example: a light switch. The switch remembers its position until flipped. * In computers: voltag..."

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Created page with "= Memory: From Relays to DRAM = This page traces the evolution of memory technology: how information was stored, from mechanical relays to modern transistor-based RAM. It explains why each step was necessary and what trade-offs were involved. == What Is Memory? == In computer science, '''memory''' is any container that holds a pattern (0/1) until it is changed. * Everyday example: a light switch. The switch remembers its position until flipped. * In computers: voltag..."

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= Memory: From Relays to DRAM =
This page traces the evolution of memory technology: how information was stored, from mechanical relays to modern transistor-based RAM.
It explains why each step was necessary and what trade-offs were involved.

== What Is Memory? ==
In computer science, '''memory''' is any container that holds a pattern (0/1) until it is changed.

* Everyday example: a light switch. The switch remembers its position until flipped.
* In computers: voltage (electrical charge) represents a bit.
* Memory is essential → without it, a CPU would have no place to store instructions or data.

== Early Physical Memory ==
Before electronics, patterns were stored in physical form:

* Punch cards – holes punched into paper represent bits. Once punched, they stay.
* Delay lines – sound waves or torsion pulses in a medium (wire, mercury tube) hold information briefly.
* Drum memory – rotating magnetic drum; data stored on the surface, accessible once per rotation.

:Limitation → access was sequential or slow. Not true “random access.”

== Relays: Electrically Controlled Switches ==
* A relay = coil + mechanical contacts.
* Electricity controls whether the contacts are open or closed.
* Multiple relays can:
* Store bits,
* Perform logic (AND, OR, NOT),
* Form early computers (e.g., Zuse Z3 in 1941).

:Advantages → electrical control, reusable, programmable.
:Drawbacks → mechanical movement = slow (few Hz), wear-out over time.

== Vacuum Tubes: Purely Electronic Switches ==
* Tubes switch or amplify signals without moving parts.
* Much faster than relays.
* Enabled the first electronic computers (ENIAC, 1940s).

:Advantages → high speed.
:Drawbacks → expensive, power-hungry, unreliable for main memory.

== Magnetic Core Memory ==
* Small ferrite rings (cores) store bits by magnetizing clockwise or counter-clockwise.
* Non-volatile (keeps information without power).
* Widely used 1955–1965; even in spacecraft until the 1980s (radiation resistant).

:Advantages → reliable, non-volatile.
:Drawbacks → bulky, expensive compared to semiconductors.

== Transistors: The Turning Point ==
* Replaced tubes in the 1950s.
* Tiny, cheap, low power.
* Today’s memories are based on field-effect transistors (FETs).

:Key effect → allowed integration of thousands → billions of transistors on a single chip.

== Memory Cells ==
A memory cell stores a single bit. There are two main designs:

=== Static RAM (SRAM) ===
* Uses 6 transistors (6T cell).
* Stable latch stores one bit indefinitely (as long as powered).
* Fast (nanoseconds), but:
* Large (takes space),
* Power-hungry,
* Expensive.

:Used mainly for caches (L1/L2/L3).

=== Dynamic RAM (DRAM) ===
* One transistor + capacitor (1T1C).
* Stores charge as “1”, absence as “0”.
* Needs refresh (capacitor leaks in nanoseconds).
* Slower than SRAM, but:
* Very dense,
* Much cheaper.

:Used for main memory (MB → GB → TB).

=== Black-box model of a cell ===
* Select line chooses the cell.
* Read/Write line decides the operation.
* Data in/out carries the bit.

== Scaling Up Over Time ==
* 1963: first integrated memory cell.
* Early 1970s: SN7489 chip, 64 bits.
* 1986: first 1-Mbit DRAM chip.
* 2018: 128-Gbit SDRAM.
* Continuous miniaturization (Moore’s Law) → exponential growth.

== Case Study: How Much RAM Do We Need? ==
* Atari 2600 (1980): only 128 bytes RAM.
* Entire game logic + graphics + sound fit into 4 KB ROM cartridges.
* Clever programming (reusing data, procedural graphics) made this possible.

== Summary ==
* Memory evolved from physical storage to electronic semiconductors.
* Each step traded cost, speed, density, and reliability.
* Modern computers use a hierarchy:
* SRAM caches (fast, small, expensive),
* DRAM main memory (slower, large, cheap),
* Non-volatile storage (SSDs, HDDs).

[[Category:Hardware and Operating Systems]]

Memory: From Relays to DRAM - Revision history