Memory Interfacing · Computer Organization · GATE CSE

Marks 1

Let WB and WT be two set associative cache organizations that use LRU algorithm for cache block replacement. WB is a write back cache and WT is a write through cache. Which of the following statements is/are FALSE?

GATE CSE 2022

Consider a set-associative cache of size 2 KB (1 KB = 2¹⁰bytes) with cache block size of 64 bytes. Assume that the cache is byte-addressable and a 32-bit address is used for accessing the cache. If the width of the tag field is 22 bits, the associativity of the cache is _______

GATE CSE 2021 Set 2

Consider a computer system with a byte-addressable primary memory of size 2³² bytes. Assume the computer system has a direct-mapped cache of size 32 KB (1 KB = 2¹⁰ bytes), and each cache block is of size 64 bytes.

The size of the tag field is ______ bits.

GATE CSE 2021 Set 1

A direct mapped cache memory of 1 MB has a block ize of 256 bytes. The cache has an access time of 3 ns and a hit rate of 94%. During a cache miss, it takes 20 ns to bring the first word of a block from the main memory, while each subsequent word takes 5 ns. The word size is 64 bits. The average memory access time in ns (round off to 1 decimal place) is _____.

GATE CSE 2020

A certain processor uses a fully associative cache of size 16 kB. The cache block size is 16 bytes. Assume that the main memory is byte addressable and uses a 32-bit address. How many bits are required for the Tag and the Index fields resectively in the addresses generated by the processor?

GATE CSE 2019

The chip select logic for a certain DRAM chip in a memory system design is shown below. Assume that the memory system has 16 address lines denoted by A₁₅ to A₀. What is the range of addresses (in hexadecimal) of the memory system that can get enabled by the chip select (CS) signal?

GATE CSE 2019

A $$32$$-bit wide main memory unit with a capacity of $$1$$ $$GB$$ is built using $$256M\,\, \times \,\,4$$-bit $$DRAM$$ chips. The number of rows of memory cells in the $$DRAM$$ chip is $${2^{14}}.$$ The time taken to perform one refresh operation is $$50$$ nanoseconds. The refresh period is $$2$$ milliseconds. The percentage (rounded to the closest integer) of the time available for performing the memory read/write operations in the main memory unit is __________.

GATE CSE 2018

A processor can support a maximum memory of $$4$$ $$GB,$$ where the memory is word-addressable (a word consists of two bytes). The size of the address bus of the processor is at least ___________ bits.

GATE CSE 2016 Set 1

Consider a machine with a byte addressable main memory of $${2^{20}}$$ bytes, block size of $$16$$ bytes and a direct mapped cache having $${2^{12}}$$ cache lines. Let the addresses of two consecutive bytes in main memory be $${\left( {E201F} \right)_{16}}$$ and $${\left( {E2020} \right)_{16}}$$. What are the tag and cache line address (in $$hex$$) for main memory address $${\left( {E201F} \right)_{16}}$$?

GATE CSE 2015 Set 3

Assume that for a certain processor, a read request takes $$50$$ nanoseconds on a cache miss and $$5$$ nanoseconds on a cache hit. Suppose while running a program, it was observed that $$80\% $$ of the processor's read requests result in a cache hit. The average read access time in nanoseconds is __________.

GATE CSE 2015 Set 2

An access sequence of cache block addresses is of length $$N$$ and contains $$n$$ unique block address. The number of unique block addresses between two consecutive accesses to the same block address is bounded above by $$k.$$ What is the miss ratio if the access sequence is passed through a cache of associativity $$A\, \ge \,k$$ exercising least-recently-used replacement policy?

GATE CSE 2014 Set 1

In a $$k$$-way set associative cache, the cache is divided into $$v$$ sets, each of which consists of $$k$$ lines. The lines of a set are placed in sequence one after another. The lines in set $$s$$ are sequenced before the lines in set $$(s+1).$$ The main memory blocks are numbered $$0$$ onwards. The main memory block numbered $$j$$ must be mapped to any one of the cache lines from

GATE CSE 2013

The amount of $$ROM$$ needed to implement a $$4$$ bit multiplier is

GATE CSE 2012

A main memory unit with a capacity of $$4$$ megabytes is built using $$1M \times 1$$-bit $$DRAM$$ chips. Each $$DRAM$$ chip has $$1K$$ rows of cells with $$1K$$ cells in each row. The time taken for a single refresh operation is $$100$$ nanoseconds. The time required to perform one refresh operation on all the cells in the memory unit is

GATE CSE 2010

How many $$32k$$ x $$1$$ $$RAM$$ chips are needed to provide a memory capacity of $$256$$ $$K$$-bytes?

GATE CSE 2009

Consider a $$4$$-way set associative cache consisting of $$128$$ lines with a line size of $$64$$ words. The $$CPU$$ generates a $$20$$-bit address of a word in main memory. The numbers of bits in the TAG, LINE and WORD fields are respectively

GATE CSE 2007

Increasing the $$RAM$$ of a computer typically improves performance because

GATE CSE 2005

More than one word are put in one cache block to

GATE CSE 2001

The main memory of a computer has $$2$$ $$cm$$ blocks while the cache has $$2$$ $$c$$ blocks. If the cache uses the set associative mapping scheme with $$2$$ blocks per set, then block $$k$$ of the main memory maps to the set:

GATE CSE 1999

A $$ROM$$ is used to store the table for multiplication of two $$8$$ bit unsigned integers. The size of $$ROM$$ required is

GATE CSE 1996

The capacity of a memory unit is defined by the number of words multiplied by the number of bits/word. How many separate address and data lines are needed for a memory of $$4K$$ $$ \times $$ $$16?$$

GATE CSE 1995

A computer system has a $$4K$$ word cache organized in block set associative manner with $$4$$ blocks per set, $$64$$ words per block. The number of bits in the $$SET$$ and $$WORD$$ fields of the main memory address format is

GATE CSE 1995

A $$ROM$$ is used to store a truth table for a binary multiplier unit that will multiply two $$4$$ bit numbers. The size of the $$ROM$$ (number of words $$ \times $$ number of bits) that is required to accommodate the truth table is $$M$$ words $$ \times $$ $$N$$ bits. Write the values of $$M$$ and $$N$$.

GATE CSE 1995

Marks 2

Consider two set-associative cache memory architectures: WBC, which uses the write back policy, and WTC, which uses the write through policy. Both of them use the LRU (Least Recently Used) block replacement policy. The cache memory is connected to the main memory. Which of the following statements is/are TRUE?

GATE CSE 2024 Set 1

A given program has 25% load/store instructions. Suppose the ideal CPI (cycles per instruction) without any memory stalls is 2. The program exhibits 2% miss rate on instruction cache and 8% miss rate on data cache. The miss penalty is 100 cycles. The speedup (rounded off to two decimal places) achieved with a perfect cache (i.e., with NO data or instruction cache misses) is ______

GATE CSE 2024 Set 1

A 4 kilobyte (KB) byte-addressable memory is realized using four 1 KB memory blocks. Two input address lines (IA4 and IA3) are connected to the chip select (CS) port of these memory blocks through a decoder as shown in the figure. The remaining ten input address lines from IA11-IA0 are connected to the address port of these blocks. The chip select (CS) is active high.

The input memory address (IA11-IA0), in decimal, for the starting locations (Addr=0) of each block (indicated as X1, X2, X3, X4 in the figure) are among the options given below. Which one of the following options is CORRECT?

GATE CSE 2023

An 8-way set associative cache of size 64 KB (1 KB = 1024 bytes) is used in a system with 32-bit address. The address is sub-divided into TAG, INDEX, and BLOCK OFFSET.

The number of bits in the TAG is __________.

GATE CSE 2023

Consider a system with 2 KB direct mapped data cache with a block size of 64 bytes. The system has a physical address space of 64 KB and a word length of 16 bits. During the execution of a program, four data words P, Q, R, and S are accessed in that order 10 times (i.e., PQRSPQRS .....). Hence, there are 40 accesses to data cache altogether. Assume that the data cache is initially empty and no other data words are accessed by the program. The addresses of the first bytes of P, Q, R, and S are 0$$\times$$A248, 0$$\times$$C28A, 0$$\times$$CA8A, and 0$$\times$$A262, respectively. For the execution of the above program, which of the following statements is/are TRUE with respect to the data cache?

GATE CSE 2022

Assume a two-level inclusive cache hierarchy, L1 and L2, where L2 is the larger of the two. Consider the following statements.

S₁ : Read misses in a write through L1 cache do not result in writebacks of dirty lines to the L2.

S₂ : Write allocate policy must be used in conjunction with write through caches and no-write allocate policy is used with writeback caches.

Which of the following statements is correct?

GATE CSE 2021 Set 2

A 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. 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?

GATE CSE 2020

A certain processor deploys a single-level cache. The cache block size is 8 words and the word size is 4 bytes. The memory system uses a $60-\mathrm{MHz}$ clock. To service a cache miss, the memory controller first takes 1 cycle to accept the starting address of the block, it then takes 3 cycles to fetch all the eight words of the block, and finally transmits the words of the requested block at the rate of 1 word per cycle. The maximum bandwidth for the memory system when the program running on the processor issues a series of read operations is _________ $\times 10^6$ bytes $/ \mathrm{sec}$.

GATE CSE 2019

The size of the physical address space of a processor is $${2^P}$$ bytes. The word length is $${2^W}$$ bytes. The capacity of cache memory is $${2^N}$$ bytes. The size of each cache block is $${2^M}$$ words. For a $$K$$-way set-associative cache memory, the length (in number of bits) of the tag field is

GATE CSE 2018

The width of the physical address on a machine is $$40$$ bits. The width of the tag field in a $$512$$ $$KB$$ $$8$$-way set associative cache is _____________ bits.

GATE CSE 2016 Set 2

A file system uses an in-memory cache to cache disk blocks. The miss rate of the cache is shown in the figure. The latency to read a block from the cache is $$1$$ $$ms$$ and to read a block from the disk is $$10$$ $$ms.$$ Assume that the cost of checking whether a block exists in the cache is negligible. Available cache sizes are in multiples of $$10$$ $$MB.$$

The smallest cache size required to ensure an average read latency of less than $$6$$ $$ms$$ is _________ $$MB.$$

GATE CSE 2016 Set 2

In designing a computer’s cache system, the cache block (or cache line) size is an important parameter. Which one of the following statements is correct in this context?

GATE CSE 2014 Set 2

Consider a main memory system that consists of 8 memory modules attached to the system bus, which is one word wide. When a write request is made, the bus is occupied for $$100$$ nanoseconds ($$ns$$) by the data, address, and control signals. During the same $$100$$ $$ns$$, and for $$500$$ $$ns$$ thereafter, the addressed memory module executes one cycle accepting and storing the data. The (internal) operation of different memory modules may overlap in time, but only one request can be on the bus at any time. The maximum number of stores (of one word each) that can be initiated in $$1$$ millisecond is ____________.

GATE CSE 2014 Set 2

If the associativity of a processor cache is doubled while keeping the capacity and block size unchanged, which one of the following is guaranteed to be NOT affected?

GATE CSE 2014 Set 2

A $$4$$-way set-associative cache memory unit with a capacity of $$16KB$$ is built using a block size of $$8$$ words. The word length is $$32$$ bits. The size of the physical address space is $$4$$ $$GB.$$ The number of bit for the TAG field is ____________.

GATE CSE 2014 Set 2

The memory access time is $$1$$ nanosecond for a read operation with a hit in cache, $$5$$ nanoseconds for a read operation with a miss in cache, $$2$$ nanoseconds for a write operation with a hit in cache and $$10$$ nanoseconds for a write operation with a miss in cache. Execution of a sequence of instructions involves $$100$$ instruction fetch operations, $$60$$ memory operand read operations and $$40$$ memory operand write operations. The cache hit-ratio is $$0.9.$$ The average memory access time (in nanoseconds) in executing the sequence of instructions is___________________.

GATE CSE 2014 Set 3

A $$RAM$$ chip has a capacity of $$1024$$ words of $$8$$ bits each $$\left( {1K \times 8} \right).$$ The number of $$2 \times 4$$ decoders with enable line needed to construct a $$16K \times 16\,\,RAM$$ from $$1K \times 8\,\,RAM$$ is

GATE CSE 2013

A computer has a $$256$$ $$K$$ Byte, $$4$$-way set associative, write back data cache with block size of $$32$$ Bytes. The processor sends $$32$$ bit addresses to the cache controller. Each cache tag director $$y$$ entry contains, in addition to address tag, $$2$$ valid bits. $$1$$ modified bit and $$1$$ replacement bit.

The size of the cache tag directory is

GATE CSE 2012

The number of bit in the tag field of an address is

GATE CSE 2012

An $$8KB$$ direct-mapped write-back cache is organized as multiple blocks, each of size $$32$$-bytes. The processor generates $$32$$-bit addresses. The cache controller maintains the tag information for each cache block comprising of the following.
$$\,\,\,\,$$$$1$$ Valid bit
$$\,\,\,\,$$$$1$$ Modified bit

As many bits as the minimum needed to identify the memory block mapped in the cache.

What is the total size of memory needed at the cache controller to store meta-data (tags) for the cache?

GATE CSE 2011

A computer system has an $$L1$$ cache, an $$L2$$ cache, and a main memory unit connected as shown below. The block size in $$L1$$ cache is $$4$$ words. The block size in $$L2$$ cache is $$16$$ words. The memory access times are $$2$$ nanoseconds, $$20$$ nanoseconds and $$200$$ nanoseconds for $$L1$$ cache, $$L2$$ cache and main memory unit respectively.

When there is a miss in both $$L1$$ cache and $$L2$$ cache, first a block is transferred from main memory to $$L2$$ cache, and then a block is transferred from $$L2$$ cache to $$L1$$ cache.
What is the total time taken for these transfers?

GATE CSE 2010

When there is a miss in $$L1$$ cache and a hit in $$L2$$ cache, a block is transferred from $$L2$$ cache to $$L1$$ cache. What is the time taken for this transfer?

GATE CSE 2010

Consider a $$4$$-way set associative cache (initially empty) with total $$16$$ cache blocks. The main memory consists of $$256$$ blocks and the request for memory blocks is in the following order:
0, 255, 1, 4, 3, 8, 133, 159, 216, 129, 63, 8, 48, 32, 73, 92, 155.

Which one of the following memory block will NOT be in cache if $$LRU$$ replacement policy is used?

GATE CSE 2009

For inclusion to hold between two cache levels $$L1$$ and $$L2$$ in a multilevel cache hierarchy, which of the following are necessary?

$$1.$$ $$L1$$ must be a write-through cache
$$2.$$ $$L2$$ must be a write-through cache
$$3.$$ The associativity of $$L2$$ must be greater than that of $$L1$$
$$4.$$ The $$L2$$ cache must be at least as large as the $$L1$$ cache

GATE CSE 2008

Consider a machine with a byte addressable main memory of $${2^{16}}$$ bytes. Assume that a direct mapped data cache consisting of $$32$$ lines of $$64$$ bytes each is used in the system. $$A\,\,50 \times 50$$ two-dimensional array of bytes is stored in the main memory starting from memory location $$1100H.$$ Assume that the data cache is initially empty. The complete array is accessed twice. Assume that the contents of the data cache do not change in between the two accesses.

How many data cache misses will occur in total?

GATE CSE 2007

Which of the following lines of the data cache will be replaced by new blocks in accessing the array?

GATE CSE 2007

Consider two cache organization: The first one is $$32$$ $$KB$$ $$2$$-way set associate with $$32$$-byte block size. The second one is of the same size but direct mapped. The size of an address is $$32$$ bits in both cases. $$A$$ $$2$$-to-$$1$$ multiplexer has latency. of $$0.6$$ $$ns$$ while a $$k$$-bit comparator has a latency of $$k/10$$ $$ns.$$ The bit latency of the set associative organization is $${h_1}$$ while that of the direct mapped one is $${h_2}.$$

The value of $${h_1}$$ is

GATE CSE 2006

The value of $${h_2}$$ is

GATE CSE 2006

A $$CPU$$ has a cache with block size $$64$$ bytes. The main memory has $$k$$ banks, each bank being $$c$$ bytes wide. Consecutive $$c$$-byte chunks are mapped on consecutive banks with wrap-around. All the $$k$$ banks can be accessed in parallel, but two accesses to the same bank must be serialized. A cache block access may involve multiple iterations of parallel bank accesses depending on the amount of data obtained by accessing all the $$k$$ banks in parallel. Each iteration requires decoding the bank numbers to be accessed in parallel and this takes $$k/2$$ $$ns.$$ The latency of one bank access is $$80$$ $$ns.$$ If $$c=2$$ and $$k=24,$$ then latency of retrieving a cache block starting at address zero from main memory is

GATE CSE 2006

Consider a direct mapped cache of size $$32$$ $$KB$$ with block size $$32$$ bytes. The $$CPU$$ generates $$32$$ bit addresses. The number of bits needed for cache indexing and the number of tag bits are respectively

GATE CSE 2005

Consider a small two-way set-associative cache memory, consisting of four blocks. For choosing the block to be replaced, uses the least recently used $$(LRU)$$ scheme. The number of cache misses for the following sequence of blocks addresses is $$8,12,0,12,8$$

GATE CSE 2004

A block -set associative cache memory consists of $$128$$ blocks divided into four block sets. The main memory consists of $$16,384$$ blocks and each blocks contains $$256$$ eight bit words.

(i) How many bits are required for addressing the main memory?

(ii) How many bits are needed to represent the TAG, SET and WORD fields?

GATE CSE 1990

Marks 5

A $$CPU$$ has $$32$$-bit memory address and a $$256$$ $$KB$$ cache memory. The cache is organized as a $$4$$-way set associative cache with cache block size of $$16$$ bytes.

(a)$$\,\,\,\,$$ What is the number of sets in the cache?
(b)$$\,\,\,\,$$ What is the size (in bits) of the tag field per cache block?
(c)$$\,\,\,\,$$ What is the number and size of comparators required for tag matching?
(d)$$\,\,\,\,$$ How many address bits are required to find the byte offset within a cache block?
(e)$$\,\,\,\,$$ What is the total amount of extra memory (in bytes) required for the tag bits?

GATE CSE 2001

A computer system has a three level memory hierarchy, with access time and hit ratios as shown below:

GATE CSE 1996 Computer Organization - Memory Interfacing Question 24 English 1

GATE CSE 1996 Computer Organization - Memory Interfacing Question 24 English 2

GATE CSE 1996 Computer Organization - Memory Interfacing Question 24 English 3

(i) What should be the minimum size of level $$1$$ and $$2$$ memories to achieve an average access time of less than $$100$$ nsec?

(ii) What is the average access time achieved using the chosen sizes of level $$1$$ and level $$2$$ memories?

GATE CSE 1996