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multiple choice

The memory access time is ______­___­___­____.
a) The time from initiation to completion of a word or byte transfer from RAM
N the cache memory that uses write-­through protocol, if a write miss occurs ________.
b) The data is written directly to the main RAM.
In pipelined RISC proces­sors, data depend­encies can be handled.
d) All of the above.
A block-­dir­ect­-mapped cache consists of a total of 32 blocks. The main memory contains
2K blocks, each consisting of 8 words. Each word is 4 bytes. Assuming a 16-bit byte-a­ddr­essable
Address space, how many bits are there in each of the Tag, Block, and Word fields?
c) Tag= 6 bits. Block=5 bits, Word= 5 bits.
A block-­ass­oci­ati­ve-­mapped cache consists of a total of 32 blocks. The main memory contains
2K blocks, each consisting of 8 words. Each word is 4 bytes. Assuming a 16-bit byte-a­ddr­essable
Address space, how many bits are there in each of the Tag, Block, and Word fields?
A) Tag= 11 bits. Block=0 bits, Word= 5 bits.
A block-­4-way associ­ati­ve-­mapped cache consists of a total of 32 blocks. The main memory
Contains 2K blocks, each consisting of 8 words. Each word is 4 bytes. Assuming a
16-bit byte-a­ddr­essable address space, how many bits are there in each of the Tag, Set, and Word fields?
B) Tag= 9 bits. Set=2 bits, Word= 5 bits.
By using the Booth algorithm recoding technique, the binary multiplier
0 1 0 0 1 1 0 1 1 1 0 will be recoded as:
A) +1 -1 0 +1 0 -1 +1 0 0 -1 0
The processor uses the Instru­ction Register (IR) to:
Keep the instru­ction to be executed until it is finished.
Q1: How many chips you need to build a memory module of size 4M8 bits, if you only have
Chips of size 256K1 bits.
a) 128
Q2: A block-­dir­ect­-as­soc­iative cache consists of a total of 64 blocks. The main memory
Contains 1K blocks, each consisting of 8 words. Each word is 4 bytes. Assuming a
16-bit byte-a­ddr­essable address space, how many bits are there in each of the Tag, Set,
And Word fields?
a) Tag= 5 bits. Block=6 bits, Word= 5 bits.
Q3: The memory access time is:
a) The time from initiation to completion of a word or byte transfer.
Q4: Compared to the static RAM, the dynamic RAM is:
a) Slower, Cheaper, Simpler, and always needs refres­hing.
Q5: The Double­-Da­ta-Rate (DDR) SDRAM:
a) Transfers data on the rising and falling edges of its own clock cycle.
Q6: The hierarchy of the memory in a computer is (starting from the proces­sor):
a) Registers, Cache, RAM, and Hard disk.
Q7: The flash memory is made of:
a) EEPROM cells.
Q1: How many chips you need to build a memory module of size 4M8 bits, if you only
Have chips of size 256K2 bits.
a) 64
Q2: A block-­direct- cache consists of a total of 32 blocks. The main memory
Contains 4K blocks, each consisting of 4 words. Each word is 4 bytes. Assuming
A 16-bit byte-a­ddr­essable address space, how many bits are there in each of the Tag,
Set, and Word fields?
a) Tag= 6 bits. Block=5 bits, Word= 4 bits.
Q8: To solve the problem of data dependency in pipelining archit­ect­ures, ------­-----:
a) Processors use data forwar­ding.
b) The compiler insert NOP operation between the instru­ctions.
c) The pipeline has to stall until the operands are ready.
d) Any of the other options.
Q9: To solve the problem of branch penalty in pipelining archit­ect­ures, ------­-----:
a) Processors use delayed branching technique.
b) Processors use branch prediction technique.
c) Processors use branch target buffer.
d) All of the other options.
Q10: The pipeline may stall because of:
a) Data depend­ency.
b) Cache miss.
c) Limited hardware resources.
d) All of the other options.
Q11: Although the throughput increases by increasing the number of stages in
The pipeline, the number of
a) The probab­ility of data dependency will increase.
b) The branch penalty will increase.
c) The cache misses may increase.
d) All of the other options
Q2: The proces­sor’s control signals are generated by:

a) Only hardware and called Hardwired approach
b) Only software and called Microp­rog­rammed approach
c) Either (a) or (b)
Q3: In pipeli­ning, to alleviate the problem of branch delayed slot problem:

a) The compiler tries to find a suitable instru­ction that precedes the branch and move it after the branch instru­ction.
Q5: The Double­-Da­ta-Rate (DDR) SDRAM:
a) Transfers data on the rising and falling edges of its own clock cycle.
Q1: By using the Booth algorithm recoding technique, the binary multiplier 0 1 0 1 1 1 0 1 0 1 1 will be:
b) a) +1 -1 +1 0 0 -1 +1 - 1 +1 0 -1
Q2: Which statement from the following is true?
a) The ripple­-carry adder is slower than the carry-­loo­kahead adder.
Q3: Which statement from the following is true?
a) The 2-dime­nsional combin­ational array is faster than sequential circuit multip­lier.
Q8: How many chips you need to build a memory module of size 1G32 bits, if you only have chips of size 128M64 bits.
a) 4
Q9: A block direct­-mapped cache consists of a total of 128 blocks. The main memory contains 64K blocks, each consisting of 16 words. Each word is 4 bytes. Assuming a 16-bit byte-a­ddr­essable address space, how many bits are there in each of the Tag, Block, and Word fields?
a) Tag= 3 bits. Block=7 bits, Word= 6 bits.
Q10: A block associ­ati­ve-­mapped cache consists of a total of 64 blocks. The main memory contains 64K blocks, each consisting of 8 words. Each word is 4 bytes. Assuming a 16-bit byte-a­ddr­essable address space, how many bits are there in each of the Tag, Block, and Word fields?
a) Tag= 11 bits. Block=0 bits, Word= 5 bits.
Q13: The access time for the hard disk is:
a) The sum of the seek time and rotational delay.
Q14: The Digital Versatile Disk stores up to 17GB because:
a) It uses two-la­yered two-sided disks, and red-light laser.
Q15: The CD-ReW­rit­ables (CD-RW) uses:
a) Three different laser powers with an organic dye and alloy of materials in the recording layer.
Q16: The magnetic hard disk is formatted as:
a) Tracks and sectors in each platter.
Q17: In virtual memory, a page fault occurs:
a) When a virtual address has no corres­ponding physical address.
Q18: Which statement is true?
a) The processor always issues a virtual address and the MMU translates it to a physical address.
Q19: In the cache memory, the no hit occurs when:
a) The tag match occurs and the valid bit is 0.
Q20: In the cache memory that uses write-back protocol, if a write miss occurs:
a) First transfer block containing the addressed word into the cache and then overwrite specific word in cached block.
Q21: The cache memory makes the RAM to appear to the processor as much faster because of:
a) The locality of reference of computer programs.
Q22: The choice of a RAM chip for a given applic­ation depends on:
a) The cost, speed, power dissip­ation, and size of the chip.
Q23: The main problem in DRAMs is:
a) They are slow and need refreshing of their contents.
Q24: The main problem in static RAMs is:
a) They use six transi­stors to build each cell.
Q25: Pipelining is used in RISC processors to:
a) Increase the proces­sor’s throug­hput.
Q26: The 5-satges in the pipelined RISC processors is in the following order:
a) Fetch, Decode, Compute, Memory, Write.
Q27: In pipelined RISC proces­sors, data depend­encies can be handled by:
a) Any one of the other options.
Q28: In pipelined RISC proces­sors, the ideal time (throuput) needed to execute one instru­ction is:
a) One clock cycle.
Q29: In pipelined RISC proces­sors, what makes the actual throughput less than the ideal one is:
a) All of the other options.
b) The stall times due to data depend­encies.
c) The branch penalties.
d) The caches misses.
Q30: The processor uses the program counter (PC) to:
a) Keep track of the address of the next instru­ction to be fetched and executed.
Q31: In pipelined RISC proces­sors, executing the instru­ction (Add R3, R4, R5) requires the following steps in order:
a) Fetch, Decode, Compute, No-action, and Write result into register.
Q32: The proces­sor’s control signals can be generated by using:
a) Either hardwired or microp­rog­ramming control
 

rate of instru­ction execution

1-GHz clock. Instru­ction statistics in a large program are as follows: Branch 20% Load 20% Store 10% Comput­ational instru­ctions 50%
90% of instru­ction fetch operations are completed in one clock cycle and 10% are completed in 4 clock cycles. On average, access to the data operands of a Load or Store, instru­ction is completed in 3 clock cycles
On average, instru­ction fetch takes 0.9+0.1x4 = 1.3 cycles. All instru­ctions, except Load and Store, take four more cycles to complete. Load and Store instru­ctions take two additional cycles, on average. Average completion time = 1.3 + (0.2 + 0.5) x 4 + (0.2 + 0.1) x 6 = 5.9 cycles Instru­ction rate = 109 /5.9 = 169.5 million instru­ctions per second
a) Access to the memory is always completed in 1 clock cycle.
Execution rate = 1x109 /5 = 200 million instru­ctions per second

chapter 5 example

Call_register R9
• Calls a subroutine whose address is in register R9:
1. Memory address <- [PC], Read memory, IR <-Memory data, PC <-[PC] <- 4
2. Decode instruction, RA <-[R9]
3. PC-Temp<-[PC], PC <-[RA]
4. RY <- [PC-Temp]
5. Register LINK <- [RY]

Q1: Assume that all memory access operations are completed in one clock cycle in a processor that has a 1-GHz clock. What is the frequency of memory access operations if Load and Store instructions constitute 20 percent of the dynamic instruction count in a program? (The dynamic count is the number of instruction executions, including the effect of program loops, which may cause some instructions to be executed more than once.) Assume that all instructions are executed in 5 clock cycles
There is one memory access to fetch each instruction. Then, 20 percent of the
instructions have a second memory access to read or write a memory
operand. On average, each instruction has 1.2 memory accesses in 5 clock cycles. Therefore, the frequency of memory accesses is (1.2/5) × 10^9
, or 240 million accesses per second.(1 Ghz= 10^9 hz)
Give the sequence of actions for a Return-from-subroutine instruction in a RISC processor. Assume that the address LINK of the general-purpose register in which the subroutine return address is stored is given in the instruction field connected to address A of the register file (IR31−27).
Whenever an instruction is loaded into the IR, the contents of the generalpurpose
register whose address is given in bits IR31−27 are read and placed
into register RA. Hence, a Return-from-subroutine instruction will cause the contents of register LINK to be read and placed in register RA.
Execution proceeds as follows:
1. Memory address←[PC], Read memory, Wait for MFC,
IR←Memory data, PC←[PC] + 4 2. Decode instruction, RA←[LINK] 3. PC←[RA] 4. No action 5. No action

At the time the instruction Load R6, 1000(R9) is fetched, R6 and R9 contain the values 4200 and 85320, respectively. Memory location 86320 contains 75900.
step 1 and 2: the values are determined by the previous instructions
stept 3: RA = 85320, RB = 4200. Step 4: RA = 85320, RB = 4200, RZ = 86320, RM= 4200. Step 5: RA = 85320, RB = 4200, RZ = 86320, RM= 4200 RY = 75900.

16M × 32 memory using 1M × 4 memory chips

A 16M module can be structured as 16 rows, each containing eight 1M x 4 chips. A 24-bit address is required. Address lines A19-0 should be connected to all chips. Address lines A23-20 should be connected to a 4-bit decoder to select one of the 16 rows.

A block-­set­-as­soc­iative cache

A block-set-associative cache consists of a total of 64 blocks, divided into 4-block sets. The main memory contains 4096 blocks, each consisting of 32 words. Assuming a 32-bit byte-addressable address space, how many bits are there in each of the Tag, Set, and Word fields?
Each block contains 128 bytes, thus requiring a 7-bit Word field. There are 16 sets, requiring a 4-bit Set field. The remaining 21 bits of the address constitute the tag field.

problem set Mult

A = 010111 and B = 110110
b) A = 110011 and B = 101100
c) A = 001111 and B = 001111

Question about the sequential circuit

how to implement multip­lic­ation of 2’s-co­mpl­ement n-bit numbers using the Booth algorithm, by clearly specifying inputs and outputs for the Control sequencer and any other changes needed around the adder and register A.
Both the A and M registers are augmented by one bit to the left to hold a sign extension bit. The adder is changed to an n + 1-bit adder. A bit is added to the right end of the Q register to implement the Booth multiplier recoding operation. It is initially set to zero. The control logic decodes the two bits at the right end of the Q register according to the Booth algorithm. The right shift is an arithmetic right shift as indicated by the repetition of the extended sign bit at the left end of the A register.
 

R2, R3, R4, R5, R6, and R7

Load R2, #A_VEC
Load R3, #B_VEC
Load R4, #3
And R5, R5, R0
 LOOP: Load R6, (R2)
Load R7, (R3)
Multiply R6, R6, R7
Add R5, R5, R6
Add R2, R2, #4
Add R3, R3, #4
Subtract R4, #1
Branch>0 LOOP
Load R7, # RESULT
Store R5. (R7)
End
ORIGIN 500
A_VEC: DATAWORD 05, -20, 10
B_VEC: DATAWORD 09, 04, 07
RESULT: RESERVE 4
R2=512, R3=524, R4=0, R5=25 R6=7 R7=524

pipeline provides forwarding paths

The result from theALU is 130 − 12 = 118. This result is available in register RZ during cycle 6. The result of the Or instru­ction, 130, is in register RY during in cycle 6. In cycle 6, the Subtract instru­ction is in the Memory stage. The unspec­ified instru­ction following the Subtract instru­ction is generating a result in the Compute stage. In cycle 7, the result of the unspec­ified instru­ction is in register RZ, and the result of the Subtract instru­ction is in register RY.

Chapter 6 execution time and speed up

Assume that 20% of the dynamic count of the instructions executed for a program are branch instructions. There are no pipeline stalls due to data dependencies. • Static branch prediction is used with a not-taken assumption. a) Determine the execution times for two cases: when 30 percent of the branches are taken, and when 70 percent of the branches are taken. b) Determine the speedup for one case relative to the other. Express the speedup as a percentage relative to 1
In first case, 30% of branches are taken but we assumed not-taken, so they are mispredicted (one cycle penalty 30% from 20% branch instructions): The value of δbranch_penalty = 0.20 × 0.30 ×1 = 0.06
In second case, 70% of branches are taken but we assumed not-taken, so they are mispredicted (one cycle penalty 70% from 20% branchs): The value of δbranch_penalty = 0.20 × 0.70 ×1 = 0.14
Using S = 1 + δbranch_penalty, the execution time:
in first case is (1.06 × N)/R and (1.14 × N)/R for the second case.
b) Because the execution time for the first case is smaller, the performance improvement as a speedup percentage is:(1.14/1.06 -1)*100=7.5%

Chapter 9

Overflow =cn ⊕ cn−1 or xn−1 yn−1( ̅sn−1) +( ̅xn−1)( ̅yn−1) sn−1
For the subtra­ction operation X−Y on 2’s-co­mpl­ement numbers X and Y • We form the 2’s-co­mpl­ement of Y and add it to X . • Set Add/Sub =0 and c0= 0 for addition. • Set Add/Sub =1 and c0 = 1 for subtra­ction
4-bit adder has four carry-out signals: c1 = G0 + P0 c0, c2 = G1 + P1G0 + P1P0 c0, c3 = G2 + P2G1 + P2P1G0 + P2P1P0 c0, c4 = G3 + P3G2 + P3P2G1 + P3P2P1G0 + P3P2P1P0 c0
A sequence of n addition cycles generates a 2n-bit product Delay = n * (adder + control delays)
For n = 32, delay is approx­imately 32  14 = 448 gate delays
Registers A and Q are shift registers, together, they hold partial product PPi while multiplier bit qi generates the signal Add/No­add.At the end of each cycle, C, A, and Q are shifted right one bit position to allow for growth of the partial product as the multiplier is shifted out of register Q

• Non-Re­storing Division:

Stage 1: Do the following two steps n times:
1. If the sign of A is 0, shift A and Q left one bit position and subtract M from A; otherwise, shift A and Q left and add M to A.
2. Now, if the sign of A is 0, set q0 to 1; otherwise, set q0 to 0.
Stage 2: If the sign of A is 1, add M to A.

example

 

Store R6, X(R8)

Memory address [PC],
Read memory,
IR  Memory data,
PC  [PC]  4
2. Decode instru­ction,
RA [R8], RB [R6]
3. RZ [RA]  Immediate value X,
RM [RB]
4. Memory address [RZ],
Memory data [RM],
Write memory
5. No action

Add R5, R6

(on Bus B) Memory address ← [PC],
Read memory, Wait for MFC, (on Bus C) IR ← Memory data,
PC ←[PC] + 4
2. Decode instru­ction
3. The contents of R5 and R6 are sent to ALU
using buses A and B,
R5 ←[R5] + [R6],
the sum is written to R5 using bus C

sequential mult UNSIGNED

13*11

Booth algorithm

booth mult example

Restoring Division

• Do the following three steps n times:
1. Shift A and Q left one bit position.
2. Subtract M from A, and place the answer back in A.
3. If the sign of A is 1, set q0 to 0 and add M back to A (that is, restore A); otherwise, set q0 to 1.

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