Q.1 What are the key properties of semiconductor memory?

Ans: They exhibit two stable (or semistable) states, which can be used to represent binary 1 and 0; they are capable of being written into (at least once), to set the state; they are capable of being read to sense the state.

Q.2 What are two senses in which the term random-access memory is used?

Ans: (1) A memory in which individual words of memory are directly accessed through wired-in addressing logic. (2) Semiconductor main memory in which it is possible both to read data from the memory and to write new data into the memory easily and rapidly.

Q.3 What is the difference between DRAM and SRAM in terms of application?

Ans: SRAM is used for cache memory (both on and off chip), and DRAM is used for main memory.

Q.4 What is the difference between DRAM and SRAM in terms of characteristics such as speed, size, and cost?

Ans: SRAMs generally have faster access times than DRAMs. DRAMS are less expensive and smaller than SRAMs.

Q.5 Explain why one type of RAM is considered to be analog and the other digital.

Ans: DRAM cell is essentially an analog device using a capacitor; the capacitor can store any charge value within a range; a threshold value determines whether the charge is interpreted as 1 or 0. A SRAM cell is a digital devicein which binary values are stored using traditional flip-flop logic-gate configurations.

Q.6 What are some applications for ROM?

Ans: Microprogrammed control unit memory; library subroutines for frequently wanted functions; system programs; function tables.

Q.7 What are the differences among EPROM, EEPROM, and flash memory?

Ans: EPROM is read and written electrically; before a write operation, all the storage cells must be erased to the same initial state by exposure of the packaged chip to ultraviolet radiation. Erasure is performed by shining an intense ultraviolet light through a window that is designed into the memory chip. EEPROM is a read mostly memory that can be written into at any time without erasing prior contents; only the byte or bytes addressed are updated. Flash memory is intermediate between EPROM and EEPROM in both cost and functionality. Like EEPROM, flash memory uses an electrical erasing technology. An entire flash memory can be erased in one or a few seconds, which is much faster than EPROM. In addition, it is possible to erase just blocks of memory rather than an entire chip. However, flash memory does not provide byte-level erasure. Like EPROM, flash memory uses only one transistor per bit, and so achieves the high density (compared with EEPROM) of EPROM.

Q.8 What is a parity bit?

Ans: A bit appended to an array of binary digits to make the sum of all the binary digits, including the parity bit, always odd (odd parity) or always even (even parity).

Q.9 How is the syndrome for the Hamming code interpreted?

Ans: A syndrome is created by the XOR of the code in a word with a calculated version of that code. Each bit of the syndrome is 0 or 1 according to if there is or is not a match in that bit position for the two inputs. If the syndrome contains all 0s, no error has been detected. If the syndrome contains one and only one bit set to 1, then an error has occurred in one of the 4 check bits. No correction is needed. If the syndrome contains more than one bit set to 1, then the numerical value of the syndrome indicates the position of the data bit in error. This data bit is inverted for correction.

Q.10 How does SDRAM differ from ordinary DRAM?

Ans: Unlike the traditional DRAM, which is asynchronous, the SDRAM exchanges data with the processor synchronized to an external clock signal and running at the full speed of the processor/memory bus without imposing wait states.