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

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

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.

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

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

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

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

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

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

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

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

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

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)

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

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

Memory/storage hierarchy

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