Memory Flashcards
What’s the primary memory?
System: registers, cache, main memory, virtual and directly accessed by CPU
What’s the secondary memory?
Hard-drives
Where must data be transferred to in secondary memory?
Main memory when needed
What’s off-line memory?
They back up process and transport data
How many bytes are in a bit?
8 bites
What’s computer memory?
Temporary storage area and it holds data and programs that CPU needs
What’s a pigeonhole analogy?
Back in WW1, pigeons were used to deliver letters across fronts
How much does a storage location hold?
One word, like an 8-bit computer, holds 8-bit words
Define ‘‘address’’
Using bytes to locate to memory and a single address can space between RAM and ROM
What’s the RAM?
Random Access Memory it’s assessed by CPU, it read and writes and it’s volatile memory where a state is lost as soon as power is cut
What’s a Static RAM?
It’s a fast, retaining state which has a high cost per bit and is used for registers, caches, buffers in I/O.
Where’s the SRAM?
RAM in embedded systems
What’s a Dynamic RAM?
Opposite to SRAM, which is slower, its bits are stored in capacitors as charges, low cost per bit and is used for large memory unit and it also needs refreshing because it discharges after some time
There are two types of DRAM, name them
SIMM and DIMM
What’s a SIMM?
A single inline memory module which had 32-bit bus width
What’s a DIMM?
A dual inline memory module which as 64-bit bus width and can store up to 32 GB.
What’s DDR and what does it do?
Double Data Rate, it transfers data on both rising and falling edges of the block signal and 2 signal per cycle compared to SDR.
Why do we need higher ‘‘confidence’’ in RAM?
Due to error-rates like we would need extra chips to handle the traffic on popular servers or government databases
What’s an LP-DDR RAM?
It’s used in mobile devices, LP stands for low power, its temperature is defined by refresh rate, it’s slower and smaller than regular DDR
Why use Virtual Memory?
We use it when the computer has little physical memory available, it’s slower than main memory.
What’s a ROM?
Read-Only Memory, it’s non-volatile and it’s used to start up your computer like BIOS.
What’s a cache?
A small amount of entire memory space is being accessed at any given time, values are accessed repeatedly
Temporal locality?
Values tend to be accessed repeated at nearby times
Sequential locality?
Same sequences tend to be re-accessed in same orders
Spatial locality?
Values nearby in memory tend to be accessed together
Level 1 Cache
Data cache to store data only
TLB
Translation lookaside buffer (TLB) cache for virtual memory
What’s a block in cache?
Copies of several contiguous words from memory
What’s a tag in cache?
Address or other ID describing which memory is copied in the block
What’s a dirty bit in cache?
Logging whether data was changed
What’s hit or miss?
Requested data is found not found, it consists of rate time and miss penalty
What’s a victim in cache?
Cached data to be thrown out to make room for new data
What’s a hash function?
It maps big data to smaller ones, usually not possible to recover original data
What’s a disadvantage of directed hash function?
That it can’t keep multiple uses of addresses in the cache if they share the same hash
What are there other mapping algorithms?
Full associative and hybrid
What’s a magnetic disk drive?
To read and write data to disk surfaces, platter spins at high speeds, 5400 RPM - 15000 RPM
What’s the meaning of Access Time?
It seeks time it takes for an arm to position itself over desired tracks
What impacts the data transfer?
The size of the data
What’s RAID?
Redundant Array of Independent Disks
What does RAID do?
Makes hard discs more resilient to failure
