Architecture II Flashcards
1
Q
What are the 4 systems of memory?
A
- Primary (system) = registers, cache, main memory, virtual; directly accessible by CPU
- secondary (online) = spinning hard-drives; data must be transferred to main memory when needed
- Tertiary (near-line) = tape libraries, optical jukebox; can be bought online quickly
- offline = optical disk, flash drive, external HDD; disconnected and used for backup purposes or transportation
- as you go down the levels the cost and speed decreases but size increases
2
Q
What is computer memory?
A
- temporary storage area that holds data and program instructions that CPU needs
- consists of many storage cells, each of which can store 1 bit
- each storage location holds one word (8-bit computers hold 8 bits in location, 16 bit ones store 16 bits)
- impractical to assign distinct addresses to individual bit locations therefore addresses refer to byte location
3
Q
What is RAM?
A
- Primary memory
- set of memory chips made of millions of transistors and capacitors
- directly accessed by CPU
- read/write
- volatile
- holds data/application programs from input devices or storages
4
Q
Difference between SRAM and DRAM
A
SRAM; -bits stored in transistors -fast, retains state -complex construction, expensive -used for registers, cache, buffers in I/O devices, RAM in embedded systems DRAM -bits stored as charge -slower, discharges after sometime -structural simplicity, cheaper -used for bulk of PC main memory, large memory units
5
Q
SRAM and DRAM implementation
A
- SRAM = 3 bit words, 2 bit addresses, combines; decoder, registers and clock switch
- DRAM = uses capacitors, new electronic component, store charge, same addressing as other RAMS
6
Q
Difference between SIMM and DIMM
A
SIMM -Single in line memory module -32 bit bus width DIMM -Dual in line memory module -64-bit bus width -predominant type of memory module in 2018
7
Q
What is DDR?
A
- Type of DRAM
- transfers data on both rising and falling edges of clock signal
- various versions with each becoming faster, more efficient, increasing in capacity and lowering in power consumption
8
Q
What is ECC RAM?
A
- error correcting ram
- used in applications where high confidence needed (in-memory databases, popular servers, government, financial etc)
- has extra chip on the DIMM which store extra copies or checksums of the data
- not commonly used as regular DRAM is good
9
Q
What is Virtual memory
A
You know
10
Q
What is ROM?
A
- persistent state (non-volatile)
- used to store firmware and BIOS
- can be written to (Morden ones)
- limited number of write/erase cycles
11
Q
Types of ROM
A
- Mask ROM = contents programmed using photolithography by manufacturer
- Programmable ROM = empty of data when the chip is manufactured; programmed by user. Cannot be erased when programmed
- erasable ROM = like PROM but the chip can be removed from computer and program erased
- Electrically EPROM = like EPROM but electricity is used to erase and reprogram selected contents
- flash memory
12
Q
What is the principle of locality?
A
- temporal locality = values tend to be accessed repeatedly at nearby times
- sequential locality = same sequences tend to be re-accessed in same orders
- spatial locality = values nearby in memory tend to be accessed together
- applies to both instructions and data
13
Q
What are the levels of cache memory?
A
- L1 includes three different sections; instruction (Harvard) cache, data cache, translation lookaside buffer cache virtual memory page tables
- L2 is shared, also L3 is a thing
- cache nowadays is located on CPU
14
Q
What is a cache line
A
- cache memory is made of cache lines
- block = copies of several contiguous words from memory
- tag = address or other ID describing which memory is copied in the block
- dirty bit = logging whether the block data is modified
15
Q
What is hit/miss?
What is the victim?
A
- requested data is found/not found
- hit/miss rate = factor of time data is found/not found (max 1)
- hit time = time required to access requested data
- miss penalty = time required to process a miss
- cached data to be thrown out to make room for new data
16
Q
What is hashing?
A
- hash function maps a big datum to a smaller one
- not usually possible to recover original from the hash data
17
Q
3 types of hashing algorithms?
A
Direct = always read and or store address and block in the same place; easy fast and cheap, different values produce same hash Associative = store tag at any available line; can cache all the best addresses at once, cost/complexity of digital logic is high Hybrid = hash address to subset of lines in cache memory then use associative rules inside these subset
18
Q
What is special about cache write?
A
- similar to reading from cache but victim cant just be thrown away, needs to be written to memory
- write through = copy to RAM and unset diary bit shortly after cache write (uses lots of bus bandwidth)
- write back = write the RAM only when victimised (slower at the time)
19
Q
What is the layout of a disk drive?
A
- each surface is divided into a number of concentric tracks
- track has same width as head and a number of sectors
- adjacent sectors and tracks are separated by gaps
- data transferred to and from disk in sectors
- each sector has a unique address
- data is accessed in a random-access manner
20
Q
What affects a disk drives performance?
A
- access time spit into; seek time (time it takes for arm to position over desired track) and rotational delay (time it takes for desired sector to position itself under head)
- transfer time = time it takes to read/write data
21
Q
What is RAID
A
- redundant array of independent discs
- method to make hard discs more resilient to failure
- use multiple discs as redundant backup and or speed up
- various architectures including; RAID1 (simple backup of complete disc), RAID5 (file striping, allows access to many parts of files at the same time
22
Q
What is I/O?
A
- any transfer of data to or from the CPU/memory combo is considered I/O
- if CPU is brain then I/O is nervous system
23
Q
How do we ensure a node can send a message to another node
A
The node must
- announce who its for
- announce the type of message
- announce the data
- ensure the above signals don’t collide with signals being sent by other nodes
24
Q
Advantages and disadvantages of the bus
A
- easy to add new devices
- low cost due to shared wires
- bottleneck; performance of the system limited by the bus
- performance limited by physical factors (wire length, number of connections)
25
Non-bus networks?
| What is bandwidth?
- point to point
- mesh networks
- bandwidth = lane speed * number of lanes
- how much data can be transferred in a time
26
What determines the size of memory?
- size of addressable locations
- width of address bus
- 32 bit systems have 2^32 amount of memory or 4GB
27
What is MAR and MBR?
- MAR hols address of read/write to go on address line
- MBR holds data to go on/retrieved from data line
- control uni connects them temporarily to the bus and adds the control one signal
28
What is the system bus and the expansion bus?
- system bus connects the CPU to main memory on the system board
- expansion bus allows the CPU o communicate with peripheral devices
29
What is an I/O module?
- any external device attaches to a computer by a link to an I/O module
- appears to the CPU and assembly programmer as an area of read/writable memory just like main RAM
- functions include; device communication, control and timing, data buffering and error detection
30
What might writing to I/O module addresses involve?
- transmit commands to the module/device
| - send data to the module/device
31
What might reading from I/O module address involve?
- read data from the module/device
| - read status information from the module/device
32
How do I/O modules handle control and timing?
- must be able to co-ordinate the flow of data between the internal resources and external devices
- devices may be slow so module manages them independent of the CPU
- this allows the CPU to go and do other things at the same time
- another form of parallelism
33
How is data sent to IO module?
- data coming from main memory is sent to a module in a rapid burst
- data is then buffered in the module and sent to peripheral device at its data rate due to the transfer rate of external devices being much sower than internal
34
How do IO modules detect errors?
- report errors to the cpu
- mechanical or electrical malfunctions reported by device
- unintentional changes to bit pattern as it is transmitted from devices to IO module
35
Difference between IO modules vs device drivers?
- IO modules are hardware connected to the bus
- device driver is a piece of software which takes sole responsibility for all communications with the IO modules or with one, or many, devices connected to it
36
What are the steps involved in transferring data from an external device to a cpu
1) CPU asks IO module to check status of device
2) IO module returns device status
3) if ready, CPU requests transfer of data
4) IO module obtains a unit of data from the device
5) Data transferred from IO module to cpu
37
What is polling?
- cpu is executing a program and encounters an instruction relating to IO operation
- cpu executes that instruction by issuing a command to appropriate IO module
- IO module performs requested action based on IO command
- IO module sets appropriate bits in IO status register
- CPU periodically checks status of IO module until it finds that operation is complete
38
Pros and cons of polling
- simple
- cpu has direct control
- very little hardware support
- cpu must periodically poll the module to check status
- ties up cpu for long period with no useful work
- cpu slowed to the speed of the peripheral
39
What is an interrupt?
- cpu issues read command
- IO module gets data from peripheral whilst CPU does other work
- IO module interrupts the CPU
- CPU requests data
- IO module transfers the data
40
Pros and cons of interrrupt?
- fast
- efficient
- tricky to write
- Done by hardware manufacturer
- still requires active interaction of cpu for data transfer between memory and IO module
41
What is DMA
- requires DMA controller on system bus
- takes IO communication over from cpu
- cpu grants authority to read from or write to memory
- relieves cpu to do other things
- DMA sends interrupt when task is complete
- cpu is only involved at beginning and end of transfer
- used for large data movement
42
What is the high performance architecture
- if many devices are connected to the bus
- data transfer demand approaches capacity of bus
- bus becomes bottleneck
- the solution is to use multiple buses laid out in a hierarchy
43
How do modern PC’S connect buses
- Northbridge = fast, connects direct to CPU, RAM, PCIe, GPU
- Southbridge = slower, all other IO modules, migrated onto single chip
- both are speed bottlenecks
44
How has IO changed over the years?
- used to be that each device needed own module, which required its own IRQ line, which required it own IO level driver
- painful to set up
- today standard lower level bus has a single IO module (USB etc), which has single IRQ and single IO level driver
- high speed level drivers then talk to devices directly over this
- eg; USB sound card has no direct line to CPU
45
What is PCIe bus
- peripheral component interconnect express
- general purpose for internal peripheral devices (graphics, networking, sound, video capture
- replacing old versions
- 1 to 32 lane versions
- speed versions (2GB-16GBs per lane)
- not a bus, actually a mesh network
46
What is a serial port
- ancient/classic point-point comes between 2 devices
- not a bus
- speed = 75-115200b/s, often 9600b/s
47
What’s USB
- standard for connecting peripheral devices
- not a bus
- replaced a variety of of earlier interfaces
- different versions and speeds; USB1: 12 Mpbs - USB3 5Gbps
- USB hubs, master and slave layout
48
What are differential signals
- USB has 4 physical wires, 5v
- bits represented by differential voltage between 2 wires
- these wired contain same information mirrored high-low
- this makes wires immune to external electrical fields
- especially when they are twisted together
49
What is IEEE1394
- FireWire
- competitor to USB
- unlike USB is an actual bus
- single channel shared by all devices, messages ID by device addresses and controlled for collisions
- can daisy chain where as USB cannot
- no fixed master, any device can take master role
50
What is SCSI
- old, 1980’s
- bus for mass storage devices (hard discs)
- pioneered moving logic and work from cpu into IO module
- reliable but expensive (used today in servers)
51
What is SATA
- competitor to SCSI
- serial ATA
- cheaper and simpler
- used in computer systems
52
What is I^2C bus
- user integrated circuit bus for connecting chips together
- common in robotics
- two wires (data and clock)
- Multi-master, multi-slave
- master:generates clock, initiates comes
- slave: replies to maser
- basic message collision avoidance: only talk if the bus is free
53
What is practical I^2C
FTDI chip
- standard way to access I2C from user code (for robotics)
- run serial port over USB in FTDI, convert to I2C
54
What is Controller Area network bus
- a vehicle bus is a specialised internal communications network that interconnects components inside a vehicle (train, ship, car etc)
- CAN is a true serial bus
55
What is Ethernet?
- a true bus
- multiple PC’s in local area all writing and reading one bus
- each message is a frame (contains MAC address)
- must avoid collisions
- bus is public so everyone can see information on it
- modern networks build non-bus features on top of basic bus (mesh and star topologies)
56
What is infiniband
- extremely fast data connection for super computers
- connect both within and between computers
- connect via Northbridge and PCIe
- wire can go out of the box, like ethernet
- blurs line between bus and network
- violates most of networking theory for speed
- not real a bus (mesh network)
57
What is gigabit ethernet?
- same as ethernet but faster
- challenging infiniband for high performance computing
- connected via PCIe/Northbridge as opposed to classic ethernet connecting via southbridge
- 10GBs ethernet in development
58
How is bus design transforming in 2018?
- replacement of parallel with fast, simple serial buses
- replacement of buses with mesh network to reduce congestion bottleneck
- everything racing to move up from southbridge>Northbridge>CPU silicon
59
What is an embedded system?
- an entire computer system built into a larger product or another device
- work well with small amounts of ram and low processing power
- user does not have to deal with complexity, they only deal with the interface
- built for a specific task
- very time critical (real time OS)
60
What are some applications of embedded systems?
- Automation
- consumer electronics
- medical electronics
- telecom
- remotes
- military
- cars
- industrial controls
61
How many embedded systems do we use?
- average home has 40-50
| - cars have over 60
62
Some examples of embedded systems?
- keyboards = convert matrix of on/off presses to ASCII-like serial code, then send via USB
- optical mouse = optical flow implemented in digital electronics
63
What is special about the design of an embedded system?
- focused on one appliation, only the hardware we need for the app
- efficiency is very important
- need to be fast, reliable, low power and price and small in size
64
Difference between general purpose embedded systems and application specific embedded systems?
- GP = use hardware, OS and software developed by different companies (ubuntu)
- AS = hardware and software are designed together and are matched
65
What is ubiquitous computing?
- Ubicomp developed by Marc Wiser, Xerox Parc in 1988
- influential cultural movement which applies embedded systems to human interaction
- natural interfaces, information visualisation, artistic, architectural and political interactions
66
What is mindful computing?
- 2010’s opposite of Ubicomp
- people are freaked out by losing control
- so present attention-focusing, tactile interfaces
- if you turn on a light - be fully at one with it
67
What components make up embedded systems?
- sensors (input)
- Actuators (output)
- Signals
- analogue/digital conversion and vise versa
68
What are sensors in embedded systems?
- capture physical/chemical analogue quantity and convert to analogue electrical quantity
- pressure, force, heat, flow, chemical, sound, vibration, light etc
69
What are actuators in embedded systems?
- put things into action or motion
| - radio signals, lights, buzzers, motors, speakers etc
70
What is motor actuation?
- a controller gives motor commands
- driver is a power amplifier (takes low power commands from controller and converts them to high power currents)
- motor converts electrical to mechanical power
- encoder senses the motor state and feeds this back to controller
71
What is a micro controller?
- marketing term, just means any processor chip sold for embedded use
- typically some system on the chip including; CPU, memory, analog/digital conversion and I/O devices
72
Pros and cons of micro controllers
- everything in one chip, small devices, can fit almost anywhere
- lower performance than desktop
- cheap
- low power consumption meaning less heat and longer battery life
- reliable
73
What type of memory do micro-controllers have?
- much smaller capacities than in PC’s
- fast sRAM, volatile, used to store temp data
- EEPROM, non-volatile
74
What are micro-controllers timers/counters
- timer = measures precisely time intervals or elapsed time, register incremented for every machine cycle
- counter = counts number of times particular event, or process occurred with respect to a clock signal. Used to count events happening outside micro-controller
- watchdog timer = auto reset of the MCU in case of failure
75
What are common word lengths for analogue digital conversion?
-8 bit, 16 bit, 32 bit
76
What are micro-controllers IO ports?
- transfer data to/from pins of the micro-controller
| - digital ports for reading/writing binary values (controlling lights or receiving input from switches)
77
How do MCU’s communicate?
- external devices (sensors, extra memory)
- other systems (host pc)
- serial communication
- synchronous buses
- radio frequency
78
What is an ardunio?
- open source hardware embedded system
| - makes IO and AVR (type of MC) programming easy
79
What is the ATmega328?
- no external memory or bus, small program and memory all on chip
- 32 reg
- IO goes straight into chip
80
What is PIC?
- brand name of microchip technology corporation in the US
- used in large series of microcontrollers of different powers, very popular with engineers
- similar to Atmel AVR
81
What are DPS’s?
- digital signal processors
- specialised architectures for handling real time signals
- features include; fixed point arithmetic representations and Harvard arch
- long pipelines for multiple ALU operations, little branching, branchless loops
82
What is a signal?
-sequence of continuous valued data
83
Difference between pi and pi2?
- pi = single core ARM11, 32 bit RISC 1GHz, GPU 1/2Gb RAM, USB HDMI
- pi2 = ARM cortex-A7 quad cores, 900Mhz, GPU 1GB DRAM, HDMI, Ethernet
84
What are PLC’s?
- programmable logic controllers
- used in industry to control factories
- must be indestructible, reliable and simple
85
What are programmable logic arrays?
- PLA’s
- standardised, mass producible logic array
- initially everything connected to everything else
- customer blows fuses at selected points to produce the circuit they wants
- fuses can only be blown once so not re-programmable
86
What are field programmable gate arrays?
- FPGA
- evolution of PLA
- simple repeated blocks containing a few gates each, standard compute components
- potential to connect everything to everything else via interconnects
- interconnect states as firmware - reprogrammable/reusable
- used for embedded devices and prototyping chips
87
What is the Turing machine?
- theoretical model of computation, not actually implemented
- proposed 100 years after analytical engine and does same thing
- helped redefine real numbers in pure maths
- mis-interpreted as a practical computer design, inflicted SERIAL thinking on us for most of the century
88
What is the relationship between transistor count and clock speed?
-smaller transistor, shorter critical path, quicker charging/discharging capacitor and faster clock
89
Power consumption formula?
- P = C * V^2 * F
| - power, capacitance, voltage, clock frequency
90
What is the current transistor trend?
- transistor count still rising but lock rate flattening sharply
- if trend continued the way it was the power and heat outputted would eventually reach the level of the suns surface
91
What is SIMD?
| What is MIMD?
- Single instruction multiple data
- eg; add 1 to every member of an array
- multiple instruction multiple data
- eg; processors all doing different things at the same time
92
What is a ripple carry adder?
| What is a carry save adder?
- ripple carry is like column addition with carry digit of sum being taken to next column
- carry save would be like teams doing the same column addition
93
What are instruction level parallelisms?
- let user write a serial program then optimise at runtime in hardware, optimisations are very local in program space and time
- can do multi stage pipeline, eager execution (execute both branches until one reaches a decision) or out of order execution
94
How do SIMD architectures work?
- use long instruction words (64 bit) to represent multiple data items at once (4 * 16bit numbers of 8*8 bit numbers)
- operate on these arrays with single instructions
- cray supercomputers 1960’s-70’s
95
What are modern SIMD instructions
- complex CISC SIMD and dedicated registers
| - moved from supercomputers to consumer PC’s
96
What is vector processing?
- add specialised very long vector registers in CPU
- load them up with data
- special institutions and ALU hardware to run SIMD instructions on them all
- different from SIMD instructions which pack the data into a single word
97
Difference between CPU and GPU hardware?
CPU
-optimised for low-latency computations with large cache and control unit
-complex pipelines fewer ALU’s
GPU
-optimised for data-parallel and high throughput computations
-DMA transfer to main RAM
-smaller cache and pipelines but thousands of ALU’s
98
What is GPU architecture?
- one host pc
- may have multiple compute devices (multiple cards), made of multiple compute units, containing multiple processing elements and maybe some shared registers and cache
99
What is GPU software?
- a work group is a group of PE’s within a CU all executing the same instruction, a work item is a processing element execution it on one datum
- kernel is a program of SIMD instructions given to a work group
100
What is VLIW?
- Very Long Instructions Words
- similar to vector arch, multiple instructions on multiple data all in a single word
- eg; single assembly instruction may contain information for add an integer in reg A to reg B, store result in C, increment register G and bit-shift register H
101
What are multi core CPU’s?
- multiple cores on one chip
- share same address space
- some cache levels are shared, some are not, tricky to get cache writes right
102
What is non uniform memory access?
- NUMA arch are single address spaces shared by processors
- access times differ according to processor and address
- used in supercomputers
103
What is the blue gene supercomputer?
| What is piz daint supercomputer?
-classic supercomputer based on custom chips
- 2018 3rd most powerful known computer
- arch is quite boring data centre style, 5k standard Intel Xeons = 240k cores with Nvidia GPU cards
- could mean an end of supercomputing as a specialist field
104
What is MPI?
- message passing interface
- standard function library for processes to send and receive discrete messages to one another
- without caring how they are transported (TCP/IP, shared memory...)
- found in HCP (high performance computing)
105
What is SPMD?
- single program multiple data
- hundreds of maintained, identical PC’s
- no shared memory, little or no communication between nodes
- connected by standard Ethernet, shared network discs
- good for data science
106
What is grid computing?
- lots of identical managed racked PC’s
| - similar to data centre
107
What is cloud computing?
- like grids but much weaker organisation
- lots of consumer grade computer working together, not identical and may be unreliable and untrustworthy
- no shared memory and little communication between nodes
- connected via public internet
- due to unreliability users must consider sending out multiple copies of jobs incase of computer failure
108
What is map-reduce?
- many cloud computing projects all evolved to use similar structures
- split task into chunks (each running same code on different data)
- map each chunk to a worker computer
- workers send back results (smaller than data), reduce these results into a single result
- software tools such as Hadoop aid in this
109
-Hadoop vs HPC applications
HPC = simulating physical things in 2d or 3D structure space
-structure is replicated in the equations
-use MPI to pass messages around it
Hadoop = data science, zillions of similar data records, little or no interaction between them, map-reduce jobs divide the work between them
110
Types of people who use HPC vs Hadoop?
- HPC = experts and professionals with years of training, specialist expensive hardware locked in rooms
- hadoop = hackers, cheap consumer hardware and map-reduce
111
What is Spinnaker?
- Spiking Neural Network Architecture
- help simulate neutral network of brain
- 1 million cores but slow unreliable messages between chips
112
What is ROS
- Robot operating system
- message passing software framework
- like MPI but higher level and therefore slower
- nodes are arbitrary programs that can run on any computer
113
What are engineering circuits?
- engineers never got hung up on Turing machines and serial programs
- instead they work with digital and circuits in which every object is alive
- No CPU’s or instructions
114
What is latency?
| What is throughput?
- latency = time to solution execution and response time
| - throughput = tasks per unit of time bandwidth
115
How does the CPU affect computer performance?
- speeds throughput, number of registers
- CPU time is the time CPU spends computing a program and does not include time spent waiting for IO
- CPU time also means time spent executing lines of code
- performance = 1/execution time
116
3 Formula’s to compare two systems
- execution time on system B/execution time on system A = n
- One system will be n times faster than the other
- can also do; performance of system A/performance on system B = n
- To work out %; system A is x% faster than B, x = (n-1)*100
117
How do we work out CPU time?
| How can we improve performance of the cpu?
- CPU time = (time/cycle)*(cycles/instruction)*(instructions/task)
- increase clock rate or reduce number of cycles needed for a task
118
How do we work out IPS?
- Instructions per second = sockets*(cores/socket)*clock*(instructions/cycle)
- used to measure non-numerical performance (database, servers, word processing etc)
119
How do we work out FLOPS?
- floating point operations per second
- sockets*(cores/socket)*(cycles/second)*(FLOPS/cycle)
- used to measure scientific numerical computing performance
120
What are the two main server metrics
- availability = (total elapsed time - sum of downtime)/total elapsed time
- reliability = (total elapsed time - sum of downtime)/number of failures
121
What is Amdahl’s law
-formula allows us to work out potential speedup of a program when using multiple processors rather than 1
S = 1/((1-f)+(f/k))
-fraction f is parallelizable
-(1-f) is serial
-k is the speed up in optimised part of the task
-s=overall speedup
-when f (parallel processes) is small the use of parallel processors has little effect
122
What are benchmarks?
- designed to mimic a particular type of workload on a component or system
- compares difference between other systems or different hardwares
123
Difference between synthetic and real world (application) benchmarks?
- synthetic benchmarks are special test programs created to impose workload on component, useful for testing individual components
- real world or application benchmarks are based on real world applications and give a much better measure of real world performance
124
What are some important factors of benchmarking?
- task type
- load conditions = normal/peak loads, stress conditions
- time = length of tests
- stats
- user = gamer, scientist, network admin etc
125
Types of benchmarking for HPC
- WHETSTONE = emphasises math/trig function speed
- LINPACK = linear algebra package
- DHRYSTONE = string and integer manipulations
126
What is SPEC
- System performance evaluation cooperative
- companies that have agreed on a set of real test programs and data
- supposed to represent typical application CPU use
- valuable indicator of performance
127
What is the fall of computer building
- 1980’s comp builders ruled and pretty much everyone had same CPU’s
- since 1990 CPU makers rule with OS defining the platform
128
What are boot processes
- power up = cpu hardwired to start with program counter
- BIOS
- Bootloader = first user facing program (eg; for OS menus)
129
What is UEFI
- uni-fined extended firmware interface
- replaces BIOS conventions
- secure boot, boot from larger hard discs (2TB +)
- CPU independent
130
What is the x86 arch?
- most successful arch so far at 40 years old
- family of CISC arch’s with 16, 32 and 64 bit versions
- began in 1968 but first proper one in 1978
131
What is a VDU?
- visual display unit
- memory mapped, write data direct to video RAM
- IO module = VDU chip, reads video RAM, interprets data as current mode
- device
132
What is a modern graphics card?
- PCIe bus connection to Northbridge
- complex IO module
- read and execute complex commands sent to its addresses
- they are church complete computers themselves
133
What is meltdown?
- poses huge security threat to many manufacturers CPU’s
- could allow user processes to access each other’s data (to steal passwords, emails or company data)
- caused by complex unintended interaction between; VM , cache, CPU kernel mode switch, speculative execution, race condition and indirect addressing
