1. Unit 2 Computer Systems HND in Computing and Systems Development
CPU and memory
Unit 2 Computer Systems
HND in Computing and Systems Development

2. CPU Highly integrated 4.31 billion transistors in 16 core Xeon
Instruction pipelining (specific circuit for each part of a process)
Superscalar (circuits in parallel)
Speed boosting (Turbo boost)
Caches

3. Caches
A CPU cache is used to reduce the amount of time required to access data from main memory
When the CPU needs to read from or write to a location in main memory it:
checks whether a copy of that data is in the cache.
If it is, then the CPU immediately reads from or writes to the cache,
This is much faster than reading from or writing to main memory.

4. Levels of cache Modern CPUs have at least three independent caches:
an instruction cache to speed up fetching instructions
a data cache to speed up fetching and storing data
a translation lookaside buffer (TLB) used to speed up virtual-to-physical address translation

5. Levels of cache
The data cache is usually organized as a hierarchy of more cache levels (L1, L2)
This example is an AMD Athlon 64
Note the L2 cache is shared with other cores

6. Cache integration The smaller caches (L1, L2) are made from SRAM
very fast, non volatile, but relatively large area
Larger caches (L3) use eDRAM (embedded)
small area, slower, requires refreshing

7. Further integration Memory controller Graphics Bus controllers
Using external memory
Bus controllers
PCIe
Direct media interface (DMI) to chipset

8. Other types of CPU Microcontrollers
Embedded in devices (washing machines etc)
processor core
Memory (small)
programmable input/output PIO
Flash memory (program storage)

9. Other types of CPU SoC (system on a chip)
Typically used in smartphones, tablets, home routers

10. Choosing CPUs What is the application? Performance Power consumption
Productivity, creativity, gaming, business, server,
Performance
Speed, cache, architecture, cores, memory support
Power consumption
Battery life, cooling
Reliability
Intermittent usage, always on, being thrashed
Graphics
Onboard, not needed
I/O
PCI lanes required

11. Intel/AMD/ARM Intel/AMD ARM High complexity
High, but reducing power consumption
Windows/OSX compatible
ARM
Simple RISC architecture
Low power consumption
Android/iOS compatibility

12. Speeds CPU clock speed Front side bus speed Memory speed Example
A multiplier of the FSB speed
Front side bus speed
Runs at the same speed as the memory
Memory speed
Depends on manufacturer’s specification
Example
CPU 3.2 GHz, multiplier 8, FSB 400 MHz, Memory DDR2-400

13. Memory DDR3 Packaged in Up to 2800 MHz ( PC3-22400 ) PC3 = DDR3
2240 = bandwidth MB/s
Packaged in
DIMM (dual inline memory module)
SODIMM (small outline DIMM)

14. Multi-channel Single channel Dual channel Quad channel
Reads from one DIMM
Dual channel
Reads from 2 DIMMS in parallel
Doubles the transfer rate
Quad channel
Reads from 4 DIMMS in parallel
Intel i7 Extreme and some Xeons

15. Storage Compared to memory Types Higher capacity Lower cost
Non volatile
Types
Solid state disks (flash) – fastest, costliest, smallest
Magnetic disks (HDD) – slower, high capacity 10TB, affordable
Optical – slower again, very cheap, Blue Ray 128GB
Tape – slowest, non random, enormous 185TB

16. Memory/storage hierarchy

17. Activity – assignment related
Select matching CPU and memory for:
A business desktop computer
A high volume web server
Refer to the choosing CPUs slide
Justify your choices