CS: Primary memory

Volatile memory

Loses data if power is turned off

Non-volatile memory

Retains data if power is turned off

Data transfer rate

Rate at which data is moved to and from a storage location

Latency

Time taken between initiating a request for a byte or word in memory, and the byte/word arriving at the processor

Three types of memory

Primary, secondary, offline

Primary memory

Directly accessible by processor, fixed within the computer, fast access speed (low latency)

What kind of memory is ROM

Primary, permanent, non-volatile memory. Bootstrap instructions. Hardwired firmware, as original ROM had soldered circuitry that could not be changed

Last thing ROM is used for

Load the OS into RAM. Then the system is controlled by the OS

SRAM vs DRAM price

DRAM is cheaper because it uses only one capacitor and one transistor per bit.

SRAM vs DRAM latency

SRAM is faster

RAM/’Main memory’

Primary, temporary, volatile memory. ‘Working memory,’ holding data and instructions currently in use. OS moved to RAM after boot-up. Two types: DRAM and SRAM

ROM location

Motherboard, often on opposite side to CPU

EEPROM

Electronically Erasable Programmable ROM. Used by more modern computers. Can be updated by users - this is called flashing.

POST

Power on self test. Part of system boot-up

BIOS

Basic input output system. Checked as one of the POST tests

Examples of volatile memory

Registers, cache, RAM

DRAM location

Not in CPU but close. Used in main memory (RAM)

SRAM location

Used in the L1 cache and CPU

DRAM

Dynamic. Have to constantly refresh power to retain data as capacitors discharge.

Random access

Memory locations take same amount of time to be reached and can be read in any order

SRAM

Static because power doesn’t need constant refreshing, since it uses memory cells known as flip flops. Doesn’t use capacitors

DRAM vs SRAM uses

DRAM used in main memory. SRAM often used in cache memory

SRAM vs DRAM space

DRAM uses less space than SRAM

L1 Cache

Holds the section of the instructions and data currently in use that will be processed imminently.

L1 Cache location

Inside the CPU

What might be held in an L1 cache?

Small parts of an image. Short text file. Small music file

Registers

High speed storage areas, found mainly in the CPU, to be very close to the processor. Holds data or instructions temporarily, while they are waiting to be processed

What could be stored in a register?

single item memory cells so one address, one instruction or one item of data

General purpose computer

A computer used for many different applications

Embedded computer

Relatively small computer system embedded into a device. Performs one or more specialised tasks.

Embedded computer ROM

Memory is mostly ROM, containing firmware - software to run the device. This includes factory settings, start-up routines, and set routines

Examples of factory settings

Radio frequency, spin speed

Examples of set routines

Take off, landing, pre-wash, spin

Embedded computer RAM

Only a few KB. Holds data for processing, e.g. user’s inputs, selections, etc.

General purpose computer ROM

Tiny amount of ROM. Holds bootstrap loader which contains start-up instructions, carrying out the POST and BIOS routine before loading the OS into RAM

General purpose computer RAM

Often 4-12 GB. Holds data and instructions currently in use, e.g. OS, apps currently in use, data being processed

Types of memory, from slowest to fastest and cheapest to most expensive

Off-line storage (tape drives etc)

Hard disk

RAM

Cache

Registers