Lecture 7: Memory Organisation Flashcards
What are the two ways data can be read in?
Little Endian and Big Endian.
Pros of Little Endian?
Conversion from 16bit to 32bit requires no arithmetic (Pad with 0s).
Pros of Big Endian?
More natural, sign is immediately apparent and strings and integers stored in same order.
Name three degrees of memory hierarchy. Describe them.
Register Memory: fastest, inside CPU, stores temp/partial results of calculations and not many.
Primary or main memory: includes RAM and cache, used for current data and code of executing programs,100x slower than registers.
Secondary memory: peripheral devices like HDDs and SSDs, for long term persistent data, 1000s of times slower than registers and often 1000s of times larger than secondary memory.
Name three degrees of memory hierarchy. Describe them.
Register Memory: fastest, inside CPU, stores temp/partial results of calculations and not many.
Primary or main memory: includes RAM and cache, used for current data and code of executing programs,100x slower than registers.
Secondary memory: peripheral devices like HDDs and SSDs, for long term persistent data, 1000s of times slower than registers and often 1000s of times larger than secondary memory.
Describe 4 different types of Primary Memory.
Dynamic RAM: volatile and temporarily stores programs.
Static RAM: faster, larger and more expensive than Dynamic RAM. Does not need to be refreshed and primarily used for cache memory.
Read Only Memory: uneditable and stores BIOS for booting OS.
Flash Style: used in USBs, cheap and non-volatile.
What are the two types of cache memory?
On-chip and off-chip.
Three types of secondary memory?
Magnetic Disks, Magnetic Tapes and Optical Disks.
What type of secondary memory might be most appropriate for backing up large amounts of data? Why?
Magnetic Tape. Cheap.
How does CD-ROM and DVD-ROM technology work? Which can store more?
Highpowered laser burns pits and lands into surface to write data. Laser is reflected off surface into sensor as it spins to read data. DVD-ROM can store more due to shorter light wavelength.
Two types of ways errors can occur?
Single bit and multibit (burst) errors.
What is Hamming Distance?
The # of bits that are different between two words.
For code with Hamming Distance, D, it can detect … errors and correct … errors.
Detect D-1 and correct (D-1)/2 errors.
Explain parity detection.
Adds an even or odd parity bit, 0 or 1, respectively, at the end of word. Hamming distance is 2 and so it can detect but not correct. It has 50% reliability.
How many parity bits do you need in a Hamming code to correct single bit errors?
Log2(n) + 1
