1. Course : AIT 204 Course Title : Computer Organization and Architecture (COA) Course Credits : 3 + 0 Course Teacher : Dr. Y R Ghodasara & Prof. K C Kamani College of Agricultural Information Technology Anand Agricultural University Anand Unit III

2. 2 MotherBoard 3. The whole computer is built up around a motherboard, and it is the most important component in the PC. The motherboard is a large printed circuit board, which has lots of chips, connectors and other electronics mounted on it. Data Exchange in Motherboard Inside the PC, data is constantly being exchanged between or via the various devices.. Most of the data exchange takes place on the motherboard itself, where all the components are connected to each other: 3 4. In relation to the PCs external devices, the motherboard functions like a central railway station. All traffic (in or out) ends up in motherboard. Motherboard contains following components. BIOS Chipset CPU Socket RAM Slots Expansion Slots Connectors Ports CMOS Battery Jumpers External Devices Connection in Motherboard 4 5. Chipset Layout of Motherboard FSB Front Side Bus PCI Peripheral Component Interconnect LPC Low Pin Count CMOS Complementary Metal Oxide Semiconductor IDE Integrated Drive Electronics BIOS Basic Input Output System SATA Serial ATA (Advance Technology Attachment) USB Universal Serial Bus 5 6. The Chipset A chipset refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product. The term chipset often refers to a specific pair of chips on the motherboard: the northbridge and the southbridge. The northbridge links the CPU to very high-speed devices, especially main memory and graphics controllers. The southbridge connects to lower-speed peripheral devices. The southbridge actually contains some on-chip integrated peripherals, such as Ethernet, USB, and audio devices. A chipset is usually designed to work with a specific family of microprocessors. Because it controls communications between the processor and external devices, the chipset plays a crucial role in determining system performance. Current manufacturers of chipsets : NVIDIA, AMD, VIA Technologies, SiS, Intel and Broadcom. Chipset Block Diagram 6 7. CPU (Central Processing Unit)/ Microprocessor CPU contains following sub components. ALU CU Set of Registers to store data temporary. The CPU Speed is depend on the Clock Rate ( Clock Speed ). Higher the Clock speed, Higher number of Instructions executed by the CPU. CPU is connected with memory using three separate Buses (inside FSB). Data Bus ( To transfer data from memory to cpu and vice versa. ) Address Bus ( To transfer address from cpu to memory ) Control Bus ( To transfer control like Read Data, Write Data etc.) 7 8. Moores Law Gordon Moore(1970) predicted that the number of transistors in processors (and hence their speed) would be able to be doubled every 18 months. 8 9. CPU Category Based on How Data is stored in Memory Big Endian Processor The most significant byte (MSB) value, which is 0Ah in our example, is stored at the memory location with the lowest address. Examples : Apple Processors (Power G4,G5) ARM Processors Little Endian Processor The least significant byte (LSB) value, 0Dh, in our example, is stored at the memory location with the lowest address. Examples : Intel Processors AMD Processors 9 10. CPU Category Based on Instruction Set RISC Processor Reduced Instruction Set Computer Small set of simple Instructions Processor Design is Simple Size of Instruction (in bits) is same for different operations. Examples : ARM Processors Motorola Processors CISC Processor Complex Instruction Set Computer Large set of complex Instructions Processor Design is Complex Size of Instruction (in bits) may vary for different operations. Examples : Intel Processors AMD Processors 10 11. Instruction Pipelining Execution of any instruction in Processor is divided into four stages. Stage 1 : Instruction Fetch (IF) Stage 2 : Instruction Decode (ID) Stage 3 : Execute Instruction (EX) Stage 4 : Write Back Result (WB) Hence it is possible to keep different instruction in different stages. IF ID EX WBInstruction 1 Clock Cycle 1 2 3 4 11 12. 12 Illustrated example 13. 13 Time Execution 0 Four instructions are waiting to be executed 1 the green instruction is fetched from memory 2 the green instruction is decoded the purple instruction is fetched from memory 3 the green instruction is executed (actual operation is performed) the purple instruction is decoded the blue instruction is fetched 4 the green instruction's results are written back to the register file or memory the purple instruction is executed the blue instruction is decoded the red instruction is fetched 5 the green instruction is completed the purple instruction is written back the blue instruction is executed the red instruction is decoded 6 The purple instruction is completed the blue instruction is written back the red instruction is executed 7 the blue instruction is completed the red instruction is written back 8 the red instruction is completed 9 All four instructions are executed 14. Instruction execution without Pipelining Clock Cycle 1 2 3 4 5 6 7 8 9 10 11 12 IF ID EX WB IF ID EX WB IF ID EX WB Instruction 1 Instruction 2 Instruction 3 Instruction execution With Pipelining Clock Cycle 1 2 3 4 5 6 7 8 9 10 11 12 IF ID EX WB IF ID EX WB IF ID EX WB An instruction pipeline is a technique used in the design of computers and other digital electronic devices to increase their instruction throughput (the number of instructions that can be executed in a unit of time). Instruction 1 Instruction 2 Instruction 3 14 15. Random Access Memory (RAM) RAM SRAM DRAM 1. Static Random Access Memory 2. Fast to access 3. Less Dense 4. Cost wise Expensive 5. Flip Flop use as storage element 6. Used in Cache Memory 7. Consumes more power 1. Dynamic Random Access Memory 2. Slow to access 3. More Dense 4. Cost wise Cheap 5. Capacitor use as storage element 6. Used in Main Memory 7. Consumes less power 15 16. DRAM SD RAM DDR RAM 1. Synchronous Dynamic RAM 2. Can run with higher clock speed 3. Data can be fetch per clock cycle (high edge) 1. Double Data Rate RAM 2. Can run with higher clock speed 3. Double data can be fetch per clock cycle (high edge + low edge) 16 17. The Memory Hierarchy Use a small array of SRAM For the CACHE (hopefully for most accesses) Use a bigger amount of DRAM For the Main memory Use a really big amount of Disk storage For the Virtual memory (i.e. everything else) 18. Famous Picture of Food Memory Hierarchy Cache Main Memory Disk Storage Cost Latency Access Freq. CPU 19. A Favorite Cache Analogy Hungry! must eat! Option 1: go to refrigerator Found eat! Latency = 1 minute Option 2: go to store Found purchase, take home, eat! Latency = 20-30 minutes Option 3: grow food! Plant, wait wait wait , harvest, eat! Latency = ~250,000 minutes (~ 6 months) Crazy fact: ratio of growing food:going to the store = 10,000 ratio of disk access:DRAM access = 20. Rehashing our terms The Architectural view of memory is: What the machine language sees Memory is just a big array of storage Breaking up the memory system into different pieces cache, main memory (made up of DRAM) and Disk storage is not architectural. The machine language doesnt know about it The processor may not know about it A new implementation may not break it up into the same pieces (or break it up at all). Caching needs to be Transparent! 21. CACHE MEMORY Cache is small high speed memory usually Static RAM (SRAM) that contains the most recently accessed pieces of main memory. In todays systems , the time it takes to bring an instruction (or piece of data) into the processor is very long when compared to the time to execute the instruction. For example, a typical access time for DRAM is 60ns. A 100 MHz processor can execute most instructions in 1 CLK or 10 ns. Therefore a bottle neck forms at the input to the processor. Cache memory helps by decreasing the time it takes to move information to and from the processor. A typical access time for SRAM is 15 ns. Therefore cache memory allows small portions of main memory to be accessed 3 to 4 times faster than DRAM (main memory). Locality of Reference The concept is that at any given time the processor will be accessing memory in a small or localized region of memory. The cache loads this region allowing the processor to access the memory region faster. This means that over 90% of the memory accesses occurs out of the high speed cache. Memory Technology Access Time Cost ( Dollar per GB ) SRAM 15-20ns $2000 3000 DRAM 60-70ns $20 100 Magnetic Disk 5,00,000 ns $2 - 3 why not replace main memory DRAM with SRAM? The main reason is cost. SRAM is several times more expensive than DRAM. Also, SRAM consumes more power and is less dense than DRAM. 21 22. Basic Cache Model Cache Memory sits between CPU and Main Memory. Cache Memory related terms. Cache Hits : When the cache contains the information requested, the transaction is said to be a cache hit. Cache Misses ; When the cache does not contain the information requested, the transaction is said to be a cache miss. Dirty Data : When data is modified within cache but not modified in main memory, the data in the cache is called dirty data. Stale Data : When data is modified within main memory but not modified in cache,the data in the cache is called stale data. 22 23. Cache Organization in Pentium Processor When developing a system with a Pentium processor, it is common to add an external cache. External cache is the second cache in a Pentium processor system, therefore it is called a Level 2 (or L2) cache. The internal processor cache is referred to as a Level 1 (or L1) cache. The names L1 and L2 do not depend on where the cache is physically located,( i.e., internal or external). Rather, it depends on what is first accessed by the processor(i.e. L1 cacheis accessed before L2 whenever a memory request is generated). Figure shows how L1 and L2 caches relate to each other in a Pentium processor system. 23 24. VIRTUALMEMORY When user starts any program in computer, program is loaded in the main memory of a computer. In multitasking operating system, user can open more than one program at a time. Physical RAM(main memory) is limited for each computer. When user starts multiple programs, sometimes all programs can not be arranged in main memory. In this situation modern operating systems use small partition of a hard disk as memory. This partition of a hard disk is known as Swap Space / Swap Partition / Virtual Memory. Any process stored in virtual memory space can not be directly executed by the processor. Thats why it is necessary to bring that process in main memory for execution. This is known as process swapping. When any process transfers from physical memory to virtual memory this transfer is known as swap out. When any process transfers from virtual memory to physical memory this transfer is known as swap in. Process swapping is controlled by an operating system program called Memory Manager. 24 25. Operating System Process 1 Process 2 Process 3 Process 4 Process 5 Physical RAM Virtual RAM swap out swap in swap partition Concept of Virtual Memory 25