Memory in Computers

Study Notes

A computer's processor has two main components: the Control Unit and the Arithmetic Logic Unit (ALU).
Every instruction follows a machine cycle: fetch, decode, execute, and store.
Executed instructions are stored in memory.
A system clock synchronizes all processor operations.

Memory holds instructions waiting to be executed, data needed for those instructions, and results of data processing.
Memory stores three basic categories: operating systems, applications, and data being processed.
Each byte of data in memory has a unique address.
Memory size is commonly measured in gigabytes (GB).

Various types of memory exist, categorized as internal (primary) or external (secondary).
Internal memory includes RAM and ROM, and different types of RAM, such as SRAM (static RAM) and DRAM (dynamic RAM), including types like SDRAM, DDR SDRAM, DDR2, DDR3, DDR4, and RDRAM. Different types of RAM have characteristics like speed, price and refresh requirements.
External memory includes storage devices and types such as optical discs, USB flash drives, memory cards, enterprise storage and cloud storage.
RAM is volatile, losing its content without power.
ROM is nonvolatile, preserving its content even without power.
Cache memory types (L1, L2, and L3) are high-speed memory that stores frequently used data and instructions, located closer to the processor. Faster access than RAM.

Memory access time is the time for the processor to read data or instructions from memory.
Memory access time is measured in milliseconds (ms), microseconds (µs), nanoseconds (ns), and picoseconds (ps).

RAM chips reside on memory modules, small circuit boards.
Motherboard slots hold memory modules.
SIMMs (Single Inline Memory Modules) have pins on both sides that connect, forming one set of contacts.
DIMMs (Dual Inline Memory Modules) have separate pins on opposite sides, forming two sets of contacts.

PROM (Programmable ROM): One-time programmable.
EPROM (Erasable PROM): Erasable and reusable, requiring UV light.
EEPROM (Electrically Erasable PROM): Erasable and reusable without UV light, entire blocks can be cleared in single operation. Programmable in-place.

Storage devices record or retrieve from storage media.
Storage capacity is the number of bytes a medium can hold.
Units used to measure storage include kilobytes (KB), megabytes (MB), gigabytes (GB), terabytes (TB), petabytes (PB), exabytes (EB), zettabytes (ZB), and yottabytes (YB).
Storage access time is the time it takes a storage device to locate an item on the medium.
Transfer rate is the speed of data and instruction transfer. Measurements include KBps, MBps, or GBps.

SSD uses flash memory for storage, managed by its own processor.
SSDs offer advantages like higher storage capacity and faster access, along with features such as less power consumption, lighter weight, and quieter operation.

Optical discs use lasers to write and read data. Flat, round, portable discs, with materials including metal, plastic, and lacquer.

USB flash drives (also called thumb drives or pen drives) are flash memory storage devices that plug into a USB port.

Enterprise storage refers to high-capacity storage solutions for businesses.
Network-attached storage (NAS), Storage area networks (SAN), and cloud storage are types of enterprise storage.

NAS is a file-level storage solution connecting to a network.
Facilitates file sharing and data backup. Suitable for small to mid-sized businesses.

SAN is a block-level storage solution connecting servers to a dedicated storage network.
Common in large enterprises.

Cloud storage is an online storage solution managed by service providers like AWS, Microsoft Azure, and Google Cloud.
Flexibility, scalability, and cost-efficiency are offered.