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Welcome to GATE CSE Doubts, where you can ask questions and receive answers from other members of the community.
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A computer system with a word length of 32 bits has a 16 MB word- addressable main memory and a 64 KB, 4-way set associative cache memory with a block size of 256 bytes. Consider the following four physical addresses represented in hexadecimal notation.

A1 = 0x42C8A4,
A2 = 0x546888,
A3 = 0x6A289C,
A4 = 0x5E4880 

Which one of the following is TRUE ?

A

A1 and A4 are mapped to different cache sets.

B

A2 and A3 are mapped to the same cache set.

C

A3 and A4 are mapped to the same cache set.

D

A1 and A3 are mapped to the same cache set.

in CO & Architecture 5 points 12 views

1 Answer

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@swami_9

 

B. A2 and A3 are mapped to the same cache set...

 

 computer system with a word length of 32 bits has a 16 MB byte-addressable main memory and a 64 KB, 4-way set associative cache memory with a block size of 256 bytes....

The memory is already byte-addressable, so there is no use of word length but it is also mentioned that system has a word length of 32 bits. Word length is mentioned so that students get confused and waste their time and mess up their exam...

Approach should be finding number of bits in the set offset….

Set bits = log(CS/BS/k) = log(64K/256/4) = 6

Now see the addresses, the address that matters to us is C8, 68,28,48 First 6 bits from the LSB side are 001000, 101000, 101000, 001000 clearly A2 and A3 are mapped to same cache sets.....

 

https://gateoverflow.in/11046/associative-address-addressable-memory-cache-blocks-lines  

 

https://gateoverflow.in/333201/gate-cse-2020-question-30 

633 points
0
given 16MB word-addressable; i know the solution for byte addressable, i don’t know for word-addressable.
0

@swami_9

Byte addressable - To represent word in memory computer uses Bytes of code. i.e. called Byte Addressable Word Addressable- It represents ordered Byte in a word.

Memory is a storage component in the Computer used to store application programs.

The Memory Chip is divided into equal parts called as “CELLS”. Each Cell is uniquely identified by a binary number called as “ADDRESS”.

For example, the Memory Chip configuration is represented as ’64 K x 8′ as shown in the figure below...

 

The following information can be obtained from the memory chip representation shown above: 1. Data Space in the Chip = 64K X 8 2. Data Space in the Cell = 8 bits 3.

Address Space in the Chip = \log_{2} (64 K)=16 bits Now we can clearly state the difference between Byte Addressable Memory & Word Addressable Memory....

 

Byte Addressable Memory Word Addressable Memory When the data space in the cell = 8 bits then the corresponding address space is called as Byte Address.

When the data space in the cell = word length of CPU then the corresponding address space is called as Word Address....

 

Based on this data storage i.e. Bytewise storage, the memory chip configuration is named as Byte Addressable Memory.

Based on this data storage i.e. Wordwise storage, the memory chip configuration is named as Word Addressable Memory.

 

For eg. : 64K X 8 chip has 16 bit Address and cell size = 8 bits (1 Byte) which means that in this chip, data is stored byte by byte...

 

For eg. : For a 16-bit CPU, 64K X 16 chip has 16 bit Address & cell size = 16 bits (Word Length of CPU) which means that in this chip, data is stored word by word.…

 

NOTE :

i) The most important point to be noted is that in case of either of Byte Address or Word Address, the address size can be any number of bits (depends on the number of cells in the chip) but the cell size differs in each case.

ii)The default memory configuration in the Computer design is Byte Addressable ....

 

https://gateoverflow.in/29401/addressable-addressable-computer-architecture-difference  

 

https://stackoverflow.com/questions/2724449/difference-between-word-addressable-and-byte-addressable  

 

https://gateoverflow.in/283734/word-and-byte-addressable  

 

https://gateoverflow.in/289686/word-addressable-gate-2004  

 

https://gateoverflow.in/333201/gate-cse-2020-question-30  

 

https://www.youtube.com/watch?v=QOrAFDZABsM 

0

@swami_9

 

given 16MB word-addressable; i know the solution for byte addressable, i don’t know for word-addressable...

A word is consecutive bytes that cpu can fetch from main memory at a time. It can be 1 byte word, 2 bytes word or 4 bytes word. It depends on computer architecture. In a 32 bit machine word size is 4 bytes and in 64 bit machine word size is 8 bytes.

So, in word addressable cpu fetches one word at a time. But, in byte addressable cpu fetches exactly 1 byte at a time.

These are old computers like intel 8008,8085 etc. In a machine with 2 bytes word, address 0 points to wod 0 that is bytes 0–1, address 1 points to word 1 that is, bytes 2–3 and so on.

But in byte addressing address 0 is bytes 0, address 1 is bytes 1 and so on....

 

https://www.bncacademy.in/tutorial/byte-vs-word-addressable.html

...