Memory Flashcards
What is primary memory ?
Lives in the system bus address space directly accessible from the CPU
What is secondary memory ?
Hard drives, Solid State Drives, All data must be transferred to the primary memory
What is tertiary memory ?
Recent versions of Offline storage
What is offline memory ?
Storage connected externally, via the I/O or manual insertion.
What is primary storage made up of ?
consists of many storage cells, each cell can hold 1 bit. Each memory location can hold 1 word (16 bits).
What are the three types of RAM?
RAM, Static RAM, Dynamic RAM
What is Static RAM ?
bits stored in flip flops, fast, retains state, complex instructions, high cost. Used in registers and cache
What is dynamic RAM ?
Bits stored in charge capacitors, slower than Static, discharges after some time, structurally simple, Low cost, used as the main bulk of the RAM
What is a memory controller ?
Maps system addresses to one RAM module
What is ECC RAM ?
Used for more confidence in RAM errors. Usually stores extra copies of data. Not commonly used as DRAM is good enough
What is LP-DDR RAM ?
Low power, can shut down parts of the RAM that are not in use. Used in phones and laptops
What is ROM ?
Limited number of write / erase cycles, non-volatile. used to store firmware
What is the Cache ?
small amount of fast memory between the CPU and the DRAM
What types of locality are there ?
Temporal locality – values tend to be accessed repeated at nearby time
Sequential locality – same sequences tend to be re-accessed
Spatial locality – memory addresses close to each other tend to be accessed together
What types of the cache are there ?
Instruction cache and data cache
What is the translation look aside buffer ?
A cache that stores the recent translations of virtual memory to physical memory
What is a memory tag ?
Addresses or IDs that describe what memory is located on the block
What is a block ?
sequence of bytes or bits
What is a dirty bit ?
Tracks whether the block has bit modified
What is hit / miss and vitcims ?
Hit / miss is whether the data is found or not
victim is the part of the cache which will be erased
What is a hash function ?
Used to map data of arbritrary size to fixed size positions
What makes up a hard disk ?
one or more rigid disks coated with magnetic material. magnetic heads mounted on moving arms for read / write.
platter spins at high speeds, each platter has tracks, each track into sections. data stored in the sectors.
What is RAID architecture ?
More reliable way of using hard disks. RAID 1 = copy data across multiple disks. RAID 5 = Split file across multiple disks
