Memory types (Cambridge International AS Computer Science)

RAM vs ROM

What is RAM?

• RAM (Random Access Memory) is primary storage that is directly connected to the CPU and holds the data and instructions that are currently in use
• RAM is volatile which means the contents of RAM are lost when the power is turned off
• For the CPU to access the data and instructions they must be copied from secondary storage
• RAM is very fast working memory, much faster than secondary storage
• RAM is read/write which means data can be read from and written to
• In comparison to ROM, it has a much larger capacity

What is ROM?

• ROM (Read Only Memory) is primary storage that holds the first instructions a computer needs to start up(Bootstrap)
• ROM contains the BIOS(Basic Input Output System)
• ROM is a small memory chip located on the computers motherboard
• ROM is fast memory, much faster than secondary storage but slower than RAM
• ROM is non-volatile which means the contents of ROM are not lost when the power is turned off
• ROM is read only which means data can only be read from
• In comparison to RAM, it has a much smaller capacity

Differences between RAM & ROM

SRAM vs DRAM

What is SRAM?

• SRAM (Static RAM) is a form of RAM that keeps data as long as power is on

• SRAM is made from flip-flops so there is no need for constant refreshing

• SRAM is used in places where speed is more important than storage size

• An example of where SRAM is used is:

  • Cache memory, where quick access to data is most important

• Very fast – faster than DRAM

• Uses less power, good for low-power devices

• Expensive to make

• Takes up more space – lower storage capacity compared to DRAM

What is DRAM?

• DRAM (Dynamic RAM) is a form of RAM that stores each bit in a tiny capacitor

• DRAM needs constant refreshing to keep the data

• DRAM is commonly used as:

  • Main memory (RAM), where larger amounts of cheaper storage is required

• Cheaper to produce than SRAM

• Higher capacity – can fit more memory in less space

• Slower than SRAM, needs time to refresh data

• Uses more power, especially during refreshing cycles

PROM vs EPROM vs EEPROM

What is PROM, EPROM & EEPROM?

• PROM, EPROM and EEPROM are all types of ROM that are programmed and reprogrammed in different ways
• Each type has a specific application in difference devices

Worked Example A computer has hardware and software.

The hardware includes different types of memory.

Complete the description of computer memory. [5]

*Random Access Memory (RAM) and Read Only Memory (ROM) are both examples of ......................................................................... memory. *

*One item that is stored in RAM is ......................................................................... . One item that is stored in ROM is ......................................................................... . RAM can be either Static RAM (SRAM) or Dynamic RAM (DRAM). *

SRAM uses transistors arranged as ......................................................................... . DRAM uses transistors and .....................

Final answer: Answer

*Random Access Memory (RAM) and Read Only Memory (ROM) are both examples of primary memory. *

One item that is stored in RAM is currently running software/data/part of the OS.

• One item that is stored in ROM is the start-up/boot-up instructions/BIOS. *

*RAM can be either Static RAM (SRAM) or Dynamic RAM (DRAM). *

*SRAM uses transistors arranged as flip-flops. *

DRAM uses transistors and capacitors.