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CSPP
Computer Systems & Professional Practise
| Question | Answer |
|---|---|
| What is the difference between RGB and CMY colour models? | RGB is additive: Adds red, green and blue to black. CMY is subtractive: Subtracts cyan, magenta and yellow from white. |
| What is the result of the following binary additions? a) 0 + 0, b) 1 + 0, c) 0 + 1, d) 1 + 1, e) 1 + 1 + 1 | a) 0, carry 0 b) 1, carry 0 c) 1, carry 0 d) 0, carry 1 e) 1, carry 1 |
| What is overflow? | When results of operations are higher than the bit amount of what can be represented. This could result in errors or lost bits. |
| Given a bit string, how would you multiply it by 16? | Shift it to the left 4 times. (2^4=16 ) |
| What is sign-and-magnitude? | A way of representing negative numbers in binary. The MSB (first bit) denotes the sign, with 1 = negative, 0 = positive. The remaining bits are the magnitude of the number. |
| Why isn’t sign-and-magnitude typically used? | It doesn’t let us define subtraction, e.g adding a positive and negative number together will not work. |
| What is Two’s complement? | A way of representing negative numbers in binary. The MSB represents the negated form of the original MSB. |
| How do you convert a negative from denary to two’s complement? | Convert it into it’s positive binary form, flip every bit, and add 1 to then umber, ignoring overflow. |
| What is fixed vs floating point numbers? | Fixed: Where a binary number has a fixed binary point Floating: The binary point is not fixed and moves around |
| How are floating point numbers represented? | A mantissa m, and exponent e. The exponent comes after the sign bit and before m. |
| How do you calculate a true exponent e given a bias b and offset exponent e*? | e = e* - b thus e* = e + b |
| What is an offset exponent? | Used instead of two’s complement so that the representations of negative numbers are ordered earlier than the representations of positive numbers. |
| What is IEEE 754? | A standard for floating point arithmetic. Consists of a sign bit, biased exponent, a mantissa with a hidden bit, and special values like infinity and NaN. |
| In logic circuits, what do the following symbols represent? 1) . 2) + 3) Ā 4) ⊕ | 1) AND 2) OR 3) Not A 4) XOR |
| What are universal gates? | NAND and NOR gates. Any Boolean function can be represented using them. |
| What are minterms and maxterms? | Minterms are AND term where each variable appears once in either true or complemented form, maxterm is for OR terms. They represent rows in truth tables where F = 1. |
| Give an example of associativity and an example of distributivity. | Associativity: a + (b + c) = (a + b) + c Distributivity: a.(b + c) = a.b + a.c |
| What is DeMorgan’s Law? | not(a . b) = not a + not b |
| What is gray coding in Karnaugh maps and why do we use them? | The specific ordering of variables along the rows and columns such that only one-bit changes between adjacent cells. Used to ensure adjacent cells represent minterms that differ by only one variable. |
| When are K-map cells considered adjacent? | When they differ by one variable (follow gray code ordering) |
| What is a don't care state in K maps? | An input combination where the output can be either 0 or 1, represented by an X. |
| What is a multiplexer and it's components? | A MUX has N control inputs, 2^N data inputs, and 1 output. They connect selected data input to the output. |
| What is a demultiplexer and it's components? | A DE-MUX has N control inputs, 1 data input, and 2^N otuputs. They connect the 1 data input to a selected output. |
| What are encoders and decoders? | Encoder: A circuit that produces a Binary input code depending on activated inputs. Converts decimal inputs (0-9) into 4-bit BCD code. Decoder: A circuit that maps an N-bit code to 2^N one-hot outputs. Converts BCD input into 1 of 10 outputs |
| What is the difference between sequential and combinational circuits? | Sequential: Output determined by inputs AND previous outputs. Combinational: Output determined solely by inputs. |
| List the properties of flipflops. | Always clocked, constructed from latches from along with additional clock signals, respond less immediately than level-sensitive latches. |
| What is a latch? | A fundemental digital circuit used to store a single bit of information. |
| What is a JK type flipflop , T type flipflop and a D type flipflop? | JK: Combine behaivour of other flipflops into one device. J and K both take a binary value. D: Stands for Data, it is a JK flipflop when J = D and K = -D. T: Toggle. J = K. |
| What is the fetch-decode-execute cycle? | A continuous instruction cycle. Computational instructions are retrieved from memory, decoded into recognizable operations, and executed to affect the CPU's current state. |
| How does the CPU retrieve instructions in the fetch cycle? | -The Program Counter holds the address of the next instruction -Sent through address bus to memory -The Control Unit issues a Read signal -The memory places the instruction on the Data bus -The Instruction Register stores this fetched instruction |
| How does the CPU interpret instructions in the decode cycle? | -The CU analyses binary instruction to understand needed action, and sends control signals to prepare for next step -Analyses the opcode, the first few bits, to know what operation to perform -Remaining bits (operands) identify where to get data |
| How does the CPU perform operations in the execute cycle? | -The CU activates necessary circuits -For arithmetic/logic, ALU performs computation -For data transfer, data is moved to or from memory or between CPU parts |
| What are the features of the 68008 vs 68000 processor architecture? | Internal registers 32 bits wide, internal data buses 16 bits wide, has an 8 bit external data bus (16 bit in 68000), 20 bit external address bus (24 bit for 68000). |
| What is Register Transfer Language? | Language used to describe operations of a microprocessor as it executes instructions. [MAR] <- [PC] means transfer contents of PC to MAR Contents of memory location 12345 written as [MS(12345)], MS = Main Store |
| What is Assembly Language? | A program language at a slightly higher level than machine code. Uses easily remembered mnemonics for each instruction, and allows memory locations and constants to be given symbolic names. |
| What is the format for assembly language typically? | <LABEL>: <OPCODE> <OPERAND(S)> | COMMENT |
| What is the memory hierarchy? | A general view of the memory systems that underpin modern computer systems. It's a pyramid, width being capacity and height being price, speed, size, etc. Registers at top and optical disk/tape at bottom. |
| What are the features of a cache? | Small, fast, temporary memory. Can have levels, with level 1 being smallest and fastest. |
| What are the four types of cache miss? | Compulsory (occur regardless of size) Capacity (not large enough to contain all needed execution blocks) Conflict (placement strategy of blocks not associative) Coherency (occur due to cache flushes) |
| What is the difference between SRAM and DRAM? | SRAM: Static RAM. Uses a flip-flop as storage element for each bit. More expensive DRAM: Dynamic RAM. For each bit, uses presence or absence of charge in a capacitor to denote 1 or 0. Requires refreshing due to natural charge leakage. |
| What is noise? | Unwanted information. Comes in various forms but is always present, limiting factors in computer systems. |
| What are some ways of detecting isolated errors? | Send the message 3 times and vote - very expensive. Add a parity bit to the message which summarises property of the message (eg even or odd) that can check to determine if it's been altered. |
| What are some ways of detecting burst errors? | Checksums - Calculate bit-column parity checksum values (e.g using even parity) Error Correcting Code - Calculate both character and bit-column parity. |
| What is RAID? | Redundant Arrays of Inexpensive Disk. Raid 0: Striping. Successive blocks on successive disk, so R/W are spread evenly. Raid 1: Mirroring. Entire data set on each disk. Survives losses. Raid 10: Striped and mirrored. |
| Describe features of an optical disk. | A change in state (pit/land) signifies data is 1. Has multiple separate error correcting schemes. Constant linear velocity, slower than hard disks. |
| What are the blockers of increasing clock speed? | RAM Latency Frequency Wall (power consumption, capacitance, light speed, etc) |
| What are 5 potential things we can do with transistors to improve performance? | More cache More complicated execution More instructions in flight (pipeline) More threads More processors |
| What are some ways of mitigating the issues with pipelining? | Deferred branch (test whether two registers are equal by subtracting, branch on zero) Branch Prediction Speculative Execution (eager, ML, etc) |
| What is the difference between micro and macro instructions? | Macro: Single standard instruction, requires multiple clock cycles, stored in RAM Micro: Low level instruction, executed in a single clock cycle, stored in processors control memory |
| State Moore’s law. | The observation that the number of transistors on a microchip doubles nearly every two years, while cost of manufacturing halves. |
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