quartz/content/notes/memory.md

title	aliases	tags
memory		cosc204

Computer memory is a series of switches (similar to the switchboard in a house). Each switch is identified by a number and is either on or off.

(High level) Programming languages allow us to name some of the locations using variables. this is easier than remembering the number of each "switch"

These switches are mostly located in RAM. But there are also switches within the CPU called registers

SRAM

Static ram is:

• made from flip flops.
• mostly used in the cpu cache or anywhere where only a small amout of memory is needed.
• comparatively expensive to DRAM

DRAM

Dynamic ram is:

• made from capacitors
• used where a large amount of memory is needed
• slower than SRAM
• inexpensive

Non volatile memory

This is often called ROM (read only memory)

• can also be called PROM, EPROM, EEPROM, FLASH (floating-gate flash cells not transistors )

Registers

• Registers are memory cells with names within the CPU.
• They hold data instructions or CPU status.

Special purpose registers

• program counter
  • stores address of current instruction
• accumulator
  • source of one of the operands
  • destination of the result
• status flags
  • individaul bits store information about results of operations
    • result of last instruction was negative, zero, or postive
    • carry from most recent arithmetic operation
    • overflow occurred during the last instruction