1. COMP 1321 Digital Infrastructure
Richard Henson
University of Worcester
October 2018

2. Week 5: Data Transfer round and off the motherboard
Learning Objectives:
Differentiate between memory and secondary storage
Explain mechanisms for data transfer on/off motherboard
Explain how storage media store data and how it can be retrieved
Explain how software tools can be used to save/recover data to/from storage media

3. CPU Architecture
Well Done, if you got those assembly language programs to work!
Hopefully, this next overview will now make more sense:
So… on to primary storage, or memory

4. CPU, Memory and Boot-up
“Booting up” requires CPU instructions to start things off…
have to be stored somewhere (in files)
starting the computer then a matter of loading all these files & their programs so they can be processed by the CPU
Where to store?
How to get the data in and out?

5. Memory…? Storage on the motherboard!
Lot of confusion…
memory - interfaces directly with CPU
held on motherboard, controlled by system clock
fast (dynamic RAM)
very fast (static RAM)
quite fast (ROM)

6. Loading Programs… https://www.youtube.com/watch?v=nwDq4adJwzM
Usually means copying them from secondary storage into memory
readily accessible to the CPU…
As the computer has to do so much…
many programs have to be loaded in a coordinated way
needs a lot of memory!

7. Fast, Faster… CPU blindingly fast
Input for a program started off very slow
punched cards (!)
keyboard…
Output?
to a printer!
Many step-ups needed to co-ordinate CPU speed with input/output speed

8. The Von Neumann Machine
Early plugboard->motherboard design to co-ordinate between components working at different speeds
first CPU, Manchester, 1948, pre-transistor
Enhanced (transistors) to store RAM electronically
allow very fast RAM to be associated directly with the CPU

9. Fastest Fast input/output to/from motherboard needed
achieved via hard disk
CPUs got even faster…
Needed even faster RAM
Internal “cache” (direct contact with registers)
External cache (sends data to/from internal cache)

10. Booting up: loading an Operating System…
Needs to be loaded into RAM
some operating systems load everything from ROM
others use a combination…
some loaded first from ROM
rest from hard disk or other source
Hard disk needs a bootable partition to load rest of operating system into RAM

11. Primary & Secondary Storage
any other form of data storage not directly interfacing with CPU via bus
accessible to CPU via i/o calls
e.g. INT 21 (Intel 8086…)
uses ports to connect electrically with CPU
external e.g. USB, Ethernet
internal e.g. SATA
Slower than primary storage

12. Virtual Memory
Use of fast(ish) secondary storage device locations as if they were primary storage locations…
hard disk (especially SSD)
storage addressed directly by the CPU
Requires programmed mapping between extra primary storage locations & secondary storage locations
adv: unlikely that the CPU will run out of “memory”
disadv: hard disk performance “falls of a cliff” when virtual memory interfaces with CPU

13. “Firmware” Needs updating (like all software)…
Software held on EPROM (erasable, programmable) chip
can’t easily be tampered with
IDEAL for low-level operating system programs, ensures rapid boot-up
also embedded applications
Needs updating (like all software)…
some flexibility to overwrite

14. Questions Is virtual memory primary or secondary storage?
What about firmware?

15. What could Stored Data Represent…
With one 1 byte word:
i.e. 1 byte per memory location
Could be many things!!!
Can be difficult to decide what the data really does represent…
e.g: data has been recovered from a location; presented as 4E (hex)
what is it… ?

16. What could “4E” represent?
Could be part of a program instruction
in assembly language
or source code (as ASCII code)
Program data
as a number
as an ASCII character…

17. More possibilities for “4E”
Over to you…
In groups…
Five minutes…

18. Putting meaning onto raw data… (1)
Single item of data… at a single location… (e.g “peeked” as 4E) could be anything!
Only find out context by studying other bytes around it…
if next byte is… 4F (hex)
and byte after that is… 57 (hex)
the ASCII codes together spell “NOW”
so the bytes are probably all ASCII codes

19. Putting meaning onto raw data… (2)
What if the next bytes were 6B and 7D?
ASCII codes would deliver… Nk}
not a proper word
data probably not ASCII codes
What else?
could be integers between 0 and 255
maybe stored variables, or constants…
Wrong to assume… keep an open mind!

20. Use of “Control Bits”
The byte could also be broken up into two nibbles of data
0100… could be an integer of value 4
1110… could be an integer of value 14
It could also be made up of 8 “Boolean” values, which could control outputs to machinery
i.e. 0 = off; 1 = on

21. Looking at Memory locations… (Peeking)
Intel 8086 tool… debug
available since early days of DOS
Debug needs –d parameter to peek…
shows 128 bytes at a time (& corresp ASCII codes)
default memory location is the start of “free” memory
locations may still contain data from previous usage
Specified memory locations can be peeked
e.g. –d 0200 for next 128 bytes starting from &0200

22. “Peeking” and “Poking”…
& … represents address (as opposed to data)
Debug –d can be used to present a whole range of memory
e.g. –d would display every byte between addresses &0200 (hex) and &0300 (hex)
Debug –e can overwrite contents of a specified location (or sequence of locations) with new data
called “poking”
potentially can crash the computer… (!)

23. Protection against memory overwrite
Operating system protects memory addresses used by “active” processes
Use of debug -e bypasses protection!!!
only protection for computer’s primary memory is to disable the debug program
but could in theory still be executed remotely, if administrative access to local computer has been granted… (!)

24. How does data get between devices?
Data usually needs to go in both directions…
DEVICE A
DEVICE B

25. Three Data Communication Alternatives
Simplex
one direction only
Example:
Broadcast data from a radio or TV mast

26. Data Transfer Half Duplex Example: one direction only at a time
Data sent along a single copper wire
first
then

27. Data Transfer Full Duplex Example: both directions simultaneously
Broadband telephone communications

28. i/o connections with the motherboard
Normally connect digital i/o devices to the motherboard via:
direct connections through “ports”
click in expansion or “daughter” cards with their own numbered ports

29. i/o Buses used with older expansion Cards
ISA = Industry Standard Association
early ( ) communications standard
speed: up to 16 MB s-1
8 or 16-bit parallel connections
PCI = Peripheral Component Interconnect
later ( ) communications standard
speed: up to 133 MB s-1
32-bit parallel connection
‘Plug and play’ – no set-up software needed, (depending on the operating system used…)

30. Early PC with Von Neumann Architecture (PCI and ISA cards) from
PCI slot
ISA slot

31. Peripheral Connectors on the Motherboard
On-board IDE slot (now legacy)
up to TWO hard disk or DVD-ROM
40-pin “ribbon” cable
On-board SCSI slot (server board)
connects a much larger number
of devices

32. Other Hard Disk connections
On-board SATA slot
thinner ribbon cable
3.5” SATA hard disk
2.5” SATA hard disk
External SATA hard disk
Connected to motherboard
via USB

33. Von Neumann architecture in practice: “STAR”
Copied from “star” arrangement for networking computers
one hub (MCH) connects fast components
hub at centre; components at ends of ‘spokes’
other hub (IOCH) connects slower components and peripherals
hubs communicate directly with each other

34. Motherboard Hubs MCH = Memory Control Hub
connects very fast devices together in a ‘star’ configuration
I(O)CH = Input-output Control Hub
connects together slower devices, also in a star configuration

35. MCH and I(O)CH from http://www.3dnews.ru/motherboard/intel-ht-chipset/

36. Motherboard with MCH and ICH from http://www. tomshardware

37. Why arrange motherboard components like this?
Longer wires…
more time to send messages (good)
degradation of message at high speed (bad)
Therefore…
important for fast components to be close together
slower components can be further apart

38. Motherboard with MCH and ICH from http://www. tomshardware
AGP slot
Socket for processor
MCH
ICH
Slots for RAM cards

39. Another PC Motherboard… from http://www. techiwarehouse

40. Next Week
Hard/Solid State disks & File Systems for efficiently reading/writing data to/from the motherboard